Hydrogen Production from Dry Reforming of Methane and ...

International Journal of Engineering Technology, Management and Applied Sciences

www.ijetmas.com August 2016, Volume 4, Issue 8, ISSN 2349-4476

1 Menderes LEVENT

Hydrogen Production from Dry Reforming of Methane and

Carbondioxide over a Rh(2wt.%)/CeO2 catalyst

Menderes LEVENT*

*Department of Chemical Engineering, Faculty of Engineering,

Uşak University, Uşak–Turkey

Abstract

Methane reforming of carbon dioxide over Rh(2wt.%)/CeO2 was studied by using a microactivity reference unit reactor

at 500-680C and a micromeritics autochem pyrex reactor at 200 to 800C with existence of a mass spectrophotometer.

Forthis purpose, different types of CuO/CeO2 catalysts were used, initially, but lower catalyst activities and lower

hydrogen yields have been found for different feed ratios of methane and carbon dioxide. Then, a Rh(2 wt.%)/CeO2

catalyst has been prepared and by loading different quantities of this catalyst into the both reactors, the kinetic

measurements of dry reforming of methane and carbon dioxide were conducted, successfully. With loading different

quantities of the latest catalyst into the reactors, individually, higher catalyst activities and higher hydrogen yields were

detected. During these reaction studies, we have achieved, also, some reduction indications in CeO2 at temperatures

higher than 500C, however,the influence of metal type on catalyst activity is very important. By selecting Rh as an

active metal, meaningful hydrogen yields have been found at the exit of both reactors. So the selected metal type(Rh) for

the prepared catalyst is one of the best metal for this particular reaction. The consumptions of CH4 and CO2 with first

order reaction has started approximately at 400 C, but it was speeded up at 550C. Determined activation energies of

CH4 and CO2 reaction at 550-680ºC were 89.4424 and 61.9309 kJ/mol, respectively.

Key Words: Dry reforming of methane and carbon dioxide, catalyst preparation, catalyst reduction, activity tests of

catalysts, hydrogen production

1. Introduction

Development of ultra-stable Ni catalysts for CO2 reforming of methane was studied by K.Tomishige and co-

workers 1. They have reported that most serious problem in CO2 reforming of methane is destruction and

deactivation of catalysts caused by carbon deposition via methane decomposition and CO

disproportionation1.

Carbon dioxide reforming of methane into syngas over Ni/-Al2O3 catalysts was studied by S.Wang, et.al.2.

They have investigated the effects of reaction parameters on catalytic activity and carbon deposition over the

catalysts. Their kinetic studies showed that the activation energy for CO production in this reaction amounted

to 80 kJ/mol and the rate of CO production could be described by a Langmuir-Hinshelwood model2.

Portugal and co-workers3, has reported a study which is related to methane and carbon dioxide reforming

over Rh catalyst with different supports. They had found that support material type has some important effects

on catalyst activity. They have suggested that Al2O3 is the best support material for a rhodium catalyst among

some other supports.

Partial oxidation of methane and reforming of methane with CO2 over supported platinum catalysts were

carried out in the temperature range of 350-900C by Souza, et.al.4. It has reported that for reforming of

methane with CO2, support plays a decisive role on catalytic stabilities4.Verykios5 has investigated

mechanistic view of CO2 reforming of methane over a Rh/Al2O3 catalyst. He had concluded that origin of

carbon formation on catalyst surface is coming, basically from CO2, and however, CH4 has a very small effect

on carbon formation to catalyst surface. CH4-CO2 reforming activities of Ni-based catalysts under fixed and

fluidized bed operations were studied by X. Chen and co-workers6. They have concluded that fluidized bed

superior to fixed bed for the catalytic CH4-CO2 reforming is an universal phenomenon.

Work performed while the author was at the Laboratory for Chemical Reaction Engineeringof the National Institute of Chemistry, Ljubljana, Slovenia

This paper is a revised and expanded version of a conference paper entitled ‘Dry reforming of methane and carbon dioxide over a Rh(2wt.%)/CeO2

catalyst’ presented at 2nd. Int. Symp. on Innov. Tech. in Eng. and Sci.(ISITES2014), 18-20 June 2014, Karabük University, Karabük, Turkey.

Corresponding Author : Menderes Levent*, *Department of Chemical Engineering, Faculty of Engineering, Uşak University, 64100 Uşak – Turkey,



2 Menderes LEVENT

F.K.Kleitz and co-workers were studied design of mesoporous silica at low acid concentrationsin triblock

copolymer-butanol-water systems, in their conclusions, SiO2/P123 molar ratio has effected strongly the mean

pore diameter, pore volume, BET specific surface area and 3 dimensional internal pore structure

connections7. With increasing in aging temperature from 80 to 160C, a narrow mean pore dimension has

been reported between 7 and 13 nm7.

Dry reforming of methane and carbon dioxide is one of the most important reaction to study, recently.

Because, CO2 emission of the world is continously increasing and resulting to temperature rises and climate

changes in different parts of the world. Methane and carbon dioxide reaction is rather complex reaction net

work. This reaction may take place with the following reactions8 :

CH4+CO2 2CO + 2H2 (Synthesis gas production reaction) (1)

CO2+H2 CO + H2O (WGSR) (2)

CO2 + 4H2O CH4 + 2H2O (Methanation reaction of carbon dioxide) (3)

CH4 + H2O CO + 3H2 (Steam Reforming of Methane) (4)

CH4 C + 2H2 (Methane cracking reaction) (5)

2CO C + CO2 ( Carbon dioxide forming reaction) (6)

The following expressions may be valid simply for calculation of some kinetic parameters related to dry

reforming of CH4 with CO2 :

TR

-E

44

'

4

A

A.ek and ..

TR

PkCkR CH

CHCH (7)

X

CHCHCHCH

CHdW

dX

dW

dX

TR

P

dW

dXFR

0

40

CH444

0

4'

4 F Wand (8)

Methane and CO2 reorming reaction has carried out over Rh/Al2O3 catalyst by Nagai and others9. With

Rh/Al2O3 catalyst, CO2+CH4 reforming reaction was conducted in a micro flow reactor at 773-973K. They

have carried out pre-catalyst studies with different CH4/CO2 ratios and CeO2 supports. They have concluded

that activity of Rh/CeO2 catalyst is less than activity of Rh/Al2O3 catalyst, but the areal activity of both

catalysts(Rh/Al2O3 and Rh/CeO2) is equal and both catalysts have been prepared by impregnation method

with 127.7 and 61.4 m2 of surface area, simultaneously.

Dry reforming of methane and carbon dioxide was studied by Donazzi et.al.10 over Rh(4%)/α-Al2O3

catalyst. They have investigated kinetics of CH4 and CO2 over Rh(4%)/α-Al2O3 at isothermal conditions

between 300-800 C with a higher void space at different feed mixtures for a short space time in a tubular

reactor.

Li and co-workers11, have investigated the effects of Rh loadings on perormance of Rh/ Al2O3 catalyst for

partial oxidation of methane to produce synthesis gas. In case of lower Rh loadings, catalyst contains higher

RhOx sites, and when lower Rh loadings are applied, reduction of catalyst by reaction mixture is become

rather difficult.

To produce hydrogen from different hydrocarbon sources, different types of copper oxide /cerium dioxide

catalysts have been developed, recently in NIC12. Mentioned catalysts have shown good activities for

ethanol-steam reforming, water gas shift and methanol-steam reforming reactions12, but, prepared

CuO/CeO2 catalysts have not shown good activities in studied temperature range (400-680C) for dry

reforming of methane and carbon dioxide raction.

Ni catalysts supported on different ceramic oxides (Al2O3, CeO2, La2O3, ZrO2) were prepared with wet

impregnation method by M.M. Barroso-Quiroga, et.,al.13.They were reported that catalyst supported on

CeO2 has a relatively good activity, but shows signs of deactivation after a certain time during the

reaction13.



3 Menderes LEVENT

A combination of experiment and modeling was used by Mc Guire and co-workers14 to investigate catalytic

dry reforming of methane with carbon dioxide in a stagnation flow reactor. Reaction pathways show that

adsorbed HCO species is an important reaction step in modeling of dry reforming of methane and carbon

dioxide reaction14.

The Mn doping nanocrystalline Co–Ce–Zr–Ox catalysts were prepared by co-precipitation method and

characterized by various physico-chemical characterization techniques (such as XRD, TPR, O2-TPD, XPS and

TPH)15. Their catalytic performances for methane reforming with CO2 to hydrogen and carbon monoxide

were investigated by N. Wang, et.al.15. In comparison with impregnated samples, Mn incorporation

promoted dispersion of nano-sized CoOx crystallites, CoOx species dispersed better in co-precipitated

catalysts15.

Silicon nitride supported nickel catalysthas prepared by impregnation using nickel nitrate solution was

employed for carbon dioxide reforming of methane. Interaction between metal and basic support makes

catalyst more resistant to sintering and coking, and thus an excellent stability16.

A few 3% Ru-Al2O3 and 2wt.% Rh-CeO2 catalysts were synthesized and tested by P. Djinovic et al.17, for

CH4–CO2 reforming activity using either CO2-rich or CO2-lean model biogas feed. CH4–CO2 reforming

activity and stability tests of both catalysts were carried out and they concluded that H2/CO molar ratio in

produced syngas can be increased either by operating at higher temperatures, or by using a feed stream with

higher CH4/CO2 ratios17. Additionally, 2wt.% Rh–CeO2catalyst was synthesized using hard template

method and characterized by means of N2 adsorption/desorption, XRD and H2-TPR methods18. During

isothermal test performed at 923 K, the 2wt.% Rh–CeO2 catalyst was exhibited stable performance and

produced syngas.

Three types of CuO/CeO2 catalysts have not shown convenient activity levels for dry reforming of methane

and carbon dioxide reaction, therefor, a new catalyst has been synthesised for the purposed reaction19. This

material was Rh(2 wt.%)/CeO2 catalyst which was prepared by using wet impregnation method. For

preparation of this new catalyst, a commercial Rh(NO3)3 aqueous solution with 30% Rh content was used. In

order to prepare this new catalyst, commercial Rh(NO3)3 solution was added,initially, drop by drop into a

certain quantity of synthesised CeO2 powder which was previously prepared by KIT-6 template method in

NIC19.By mixing continously the content of a glass cup with a magnetic stirrer at 400 rev/min of stirring

speed, and by keeping pH of mixture below 5.5, for a certain time, purposed catalyst mixture was prepared,

simultaneously. Then, by filtering solution and by drying obtained mixture at 105C for 1 hour, ceria based

rhodium catalyst was prepared. Determined BET surface area of the latest prepared catalyst with wet

impregnation method was 121.3780 m2/gr. This latest catalyst has shown good activity values at studied

operation conditions (500C-680C) for CH4+CO2 dry reforming reaction19.

2. Experimental

2.1.Methodof measurement and gas analysis with microactivity reference unit reactor

For methane and carbon dioxide dry reforming reaction studies and catalyst activity tests, a computer

controlled microactivite reference unit reactor has used at temperature range of 20-700 C and pressure range

of 0-100 bars. The microactivite reference unit reactor of NIC has been developed recently, by PID

engineering and technology company in Spain. The reactor employed in this study has a length of 305 mm,

internal diameter of 9 mm and made of stainless steel. The company recommendation for maximum operation

temperature was 700C and recommended maximum operational pressure was 1350 bars at 25C19.

For the measurement purposes of feed, 4 thermal mass flowmeterswere mounted, already on back of the

system by producer company19. The first of those valves was for measurements of N2 gas flowrates, second

valve wasused for measurements of He flowrates, third valve was for O2 gas and fourth valve was for

measurements of H2 gas flowrates. During this studies, fourth feed line was used for feed flowrates

measurements of CH4+CO2 mixture19. All these flowmeters were computer controlled which have

adjustable gas flowrates for the each feed line on a mean local control panel. The system’s operating

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4 Menderes LEVENT

parameters(flowrates, temperatures and pressures) can be adjusted with continous observation on this

monitor19.

Reaction measurements of dry reforming of methane and carbon dioxide and the activity tests of synthesised

catalysts(different types of CuO/CeO2 catalysts) have been carried out in such a microactivite reference

unit19. By loading 100-300 miligrammes of different CuO/CeO2 type catalysts, and Rh(2 wt.%)/CeO2

catalyst into the reactor, the compositions of inlet gas mixtures and compositions of exit gas mixtures were

determined. Product mixtures were observed continously, and reactor effluent gas mixtures were analyzed by

an Agilent model gas chromatography19.

Before starting to activity tests, of different catalysts for CH4 and CO2 mixture, GC was calibrated with a

commercially provided standart gas mixture. The percentage quantities of each gas sample were found by

comparisions with compositions of commercially provided standart gas mixtures19.

After setting up feed flows of the system, activity tests of Rh(2 wt.%)/CeO2 catalyst were carried out in

microactivity reference unit reactor. All parameters related to the gas samples were monitored continously for

different operation conditions of the reactor, the exit gas compositions were analyzed and stored in a

computer19.

By regulating operational conditions and by online connection of gas chromatography gas analysis were

performed. The optimum analysis time of each sample for CH4+CO2 reaction have determined as 31 minutes.

For gas analysis of investigated reaction, TCD detector was the most appropriate detector, so that gas analysis

were carried out with TCD detector. For gas analysis, GC had arranged already with two columns. The first

column was a porapak Q column and second column was a capillary molecular sieve 5A column.

2.2. Catalyst activity studies within microactivity reference unit reactor

First of all, a small quantity high temperature resistant glass wool was placed into the reactor bottom.Then an

appropriate quantity catalyst was weighed with a precision balance.Then, catalyst was loaded into the reactor

before catalyst conditioning measurements. Then, reactor has replaced and gas leaking tests were carried out,

then, by closing reactor oven door and adjusting the appropriate feed flowrates, experimental measurements

were realized.

By connecting CO, He and CH4+CO2 mixture of gas feeds to inlet of the system, the reactor system has been

prepared for experimental programme. Loaded catalyst was conditioned at 400C with 25 ml/min of CO and

100 ml/min of He feeds for a duration of 1 hour. In the steps of catalyst reduction usually, observed pressure

drops were 1.1-1.2 bars through catalyst bed of the reactor19.

After completion of the reduction catalyst, some reaction studies were carried out with CuCe15-KIT-6 catalyst

at different experimental conditions within microactivity reference unit reactor. Dry reforming reaction of

methane and carbon dioxide has investigated in temperatures from 450C up to 680C. By adjusting the CH4

+ CO2 mixture feed flowrate to 40 and 80 ml/min and by adjusting helium flowrate to 160 ml/min, significant

values of H2 could not detected at the reactor effluent. However, various quantities of H2O, CO, CH4 and CO2

values were determined. Latest feed conditions have been tried, especially, to realise a comparison possibility

of experimental measurements of autochem equipment with experimental measurements of microactivity

reference unit reactor19.

Due to existed reversible water-gas shift reaction(WGSR) over CuCe15-impregnated and CuCe20-

impregnated catalyst at desired study conditions, and because the bad activity of these catalysts for CH4+CO2

reaction, were caused for us try to use CuCe10-co-precipitated catalyst in CH4+CO2 reaction. With 20 ml/min

CH4+CO2 mixture and 80 ml/min He feeds to the system at 450C-680C, any H2 values were not determined

at the exit gas composition. Because of observed lower activity values of this catalyst and other catalysts, we

have stopped to use this and other CuO/CeO2 catalysts for intended CH4+CO2 reaction19.

2.3. Method of study with micromeritics autochem pyrex glass reactor

For investigation of catalyst activities at 300-800 C, an online mass spectophotometer was connected to the

exit of the system for purposed reaction. Reaction products were analysed via this mass spectophotometer,

with combination of a FTIR and a IR gas analyser equipment.



5 Menderes LEVENT

For dry reforming of methane and carbon dioxide reaction, 150 mg CuCe10-impregnated, CuCe15-

impregnated and CuCe20-impregnated catalysts, were loaded into the micromeritics autochem reactor,

individually. Then, TPR and TPD tests for above types of catalysts were carried out. By setting up reactor

temperature to 500 C, TPR tests of these catalysts were conducted with accompaintment of 50 ml/min of

total feed. By adjusting operational temperature to 700 C, TPD tests of these catalysts were carried out with

same manner. It has been observed that major quantities of carbonates and oxides contents of catalysts were

consumed around temperature of 400 C during catalyst reduction studies. But, it has seen that some types of

carbonates were not decomposed on catalyst surfaces even by heating up to 600C and further temperatures.

For the above types catalysts with 50 ml/min of feed flowrate(5 % H2/He or 5% CO in Ar), the best

conditioning temperature was found to be 400 C 19.

2.4. Synthesis method of Rh(2wt%)/CeO2 catalyst

Appropriate quantity of commercial (Rh(NO3)3.H2O) (36% Rhodium based) aqueous solution was added into

25 ml of ethanol. This commercial Rh based solution was added slowly into 3.08 grammes CeO2 in order to

provide penetration solution and to fill the CeO2 porous system, completely. The mixture was stirred at 400

rpm and at room temperature for a duration of 1 hour. After this procedure, solid was dried at 60C during

night. Obtained catalyst pre-substance was put into a ceramic crucible and was kept in an oven at 550C. And

in order to decompose nirate type substances completely , this mixture was kept at 400C in here for three

hours19.

Impregnation stage of catalyst preparation were repeated with 10 ml of ethanol-metal solution. After drying

procedure at 60C during night, catalyst pre-material was re-calcined at 550C for three hours. With this

procedure, Rh(2wt.%)/CeO2 catalyst was produced(obtained) by the “wet impregnation method”19.

2.5. Method of TPR and TPD analysis of Rh(2wt.%)/CeO2 catalystwith micromeritics autochem

equipment

Temperature programmed reduction(TPR) and temperature programmed desorption(TPD) experiments for

Rh(2wt.%)/CeO2 catalyst were performed19 within micromeritics autochem eqipment. By setting total

flowrate of both gases to 25 ml/min and programming temperature to 500C, reduction experiments were

continued for 2 hours. We have started up this process by loading 150 mg impregnated

catalyst(Rh(2wt.%)/CeO2) into autochem glass reactor with accompaniment of cold trap. But, operational

pressure of autochem system was raised to above upper limit of operational pressure which was 1300

mmHg19.

Therefore, TPR experiment was stopped, immediately and remainder catalyst was taken off from the glass

reactor, and then catalyst quantity was reduced to 104.5 mg. With the same method another proper cold trap

was prepared (by adding 1.5 liters nitrogen into a proper quantity of iso-propyl alcohol) and then, TPR

experiment was restarted with existence of new cold trap, again. Observed operation pressure was found as

792 mmHg, therefore experimental measurements were continued confidently19.

After the TPR experimental measurements stage, temperature programmed desorption(TPD) experimental

measurements were continued with micromeritics autochem equipment. During TPD experiments,

temperature of autochem equipment was programmed as 700C.TCD detector response data from autochem

equipment was recorded via mass spectrophotometry. TPD experimental measurements were continued at

759 mmHg pressure for a duration of 4 hours19.

2.6. XRD analysis, method of surface area measurement and carbon analysis of remainder catalyst

XRD analysis of Rh(2 wt.%)/CeO2 catalyst was carried out at room temperature with an XRD

equipment(PANalytical X'Pert PRO). BET surface area of 0.2384 gramme powder Rh(2 wt.%)/CeO2 catalyst

has been determined with a micromeritics surface measurement equipment. Firstly, degasing process of

sample was carried out and process was completed, approximateley in a time period of 17 hours.

TOC analysis method was based on high temperature catalytic oxidation. TOC analyser has an IR detector

which was operated at 680C for determination of carbon in the remainder Rh(2 wt.%)/CeO2 catalyst sample.

By using TOC analysis method, elemental carbon was determined for the rest of the catalyst samples of



6 Menderes LEVENT

microactivity reference unit and autochem equipment. For this procedure, first of all, sample was preheated up

to 800C. Then, sample was taken into TOC equipment analysis. Finally, temperature of TOC was reduced

gradually to room temperature[19].

3. Results, discussions and interpretations

3.1. Results and discussion for CuO/CeO2 based catalysts

In this study, the reaction of dry reforming of methane with carbon dioxide, different forms of CuO/CeO2

catalysts and a Rh(2 wt.%)/CeO2 catalyst were used. In conducted experiments of dry reforming of methane

and carbon dioxide with different types of CuO/CeO2 catalysts, the lower activity values have been found.

With 20 ml/min flow of CH4+CO2 mixture and 80 ml/min He flowrate with accompaniment of 150-300 mg

CuCe15 and CuCe20 catalysts, any significant hydrogen was not found at temperature range of 600C-687C

in the exit of microactivite reference unit reactor. This was a strong evidence of lower activity of different

types of CuO/CeO2 catalysts at 400-680C temperature range. However, for CH4+CO2 reaction with above

types catalysts, a small quantity of water, some carbon monoxide, carbon dioxide and methane were

determined but any significant hydrogen was not seen at the exit of reactor system19.

In order to determine the types of unreduced oxides with different carrier gas compositions (5% H2/He, 5%

CO/He, 10% CO/Ar, 10% H2/He, 5% NH3/Ar), accumulated and unreduced oxide forms over different

catalyst surfaces have been studied at different temperatures(400-680C) during the reduction process. Some

formed oxides were not possible to remove in studied temperature range, on surface catalyst materials in spite

of higher temperatures at different ratios of reductive carrier mixtures (CO/He, NH3/He, H2/He).Thus, it was

seen some oxides were permanent on catalyst surfaces. By taking 150 or 300 mg samples from each CuCe10,

CuCe15, and CuCe20-co-precipitated catalysts, activity tests of above discussed catalysts were carried out

during CH4 and CO2 dry reforming reaction with both autochem and microactivite reference unit reactors[19].

In conducted CuCe15 catalyst activity tests, any significant hydrogen was not determined at 650C with 20

and 30 ml/min CH4+CO2 feeds, and 80 ml/min helium feed to the reactor. Reaction of dry reforming of CH4

and CO2 was took place with beginning attemperature of 500C. This fact, was proved by making comparison

with obtained results of autochem equipment19. But, formed H2 percentages of reaction at 500C was

always lower than < 5 % in total gas mixture of rector exit. But, within studied temperature range(450C-

687C), CuCe15 catalyst has not shown any good activities. Consequently, some water vapour was

determined at the exit of microactivity refrence reactor. So this may be a very good evidence shows that

observed reaction(CH4+CO2 reaction) is taking place in lower rates, and also, very small proportion of reverse

water gas shift reaction was taking place, simultaneously19.

When we have looked to previous studies of same Laboratory12, different types CuO/CeO2-KIT-6 catalysts

have shown very good activity levels for the water-gas shift, methanol-steam reforming and ethanol steam

reforming reactions12. With different flowrates (20 and 30 ml/min of CH4+CO2) by loading 150 and 300

mg(CuCe15, CuCe20and CuCe10) co-precipitated catalysts within both reactors were not maintained any

appropriate activities,in the temperature range of 400-680C19.

Consequently, above mentioned catalysts have not shown any convenient activities for dry reforming of

methane reaction with carbon dioxide. And so, we may conclude that by using different types of above

CuO/CeO2 catalysts will not be suitable for this reaction, because, the lower proportions of synthesis gas were

produced, and also above catalysts, are usually suitable to use upto 550C, but CH4+CO2 reaction rate was

speeding up at higher temperatures(above 600C). As a consequence of lower activities of above catalysis, the

synthesis of a Rh(2 wt.%)/CeO2 catalyst was performed. And an application of Rh(2 wt.%)/CeO2 catalyst for

production of hydrogen was realized successfully in catalytic reaction laboratory of NIC[19].

3.2. Results and discussions of XRD, surface area determinations and TOC analysis of Rh(2wt.%)/CeO2

catalyst

Fresh catalyst has very low rhodium metal percentage in a possible oxide form of RhO2/CeO2, so that absolute

quantity of rhodium was not seen, exactly on graph of Fig.1. But, some higher piks of CeO2 were determined

at different 2 angles of XRD equipmentas seen in Fig.1[19].



7 Menderes LEVENT

In consequence of fact that conducted analysis with micromeritics surface measurement equipment,

determined BETsurface area of the latest prepared Rh(2 wt.%)/CeO2 catalyst was 121.378 m2/gr19. This

surface area of catalyst has been confirmed well with similar catalyst studies of literature[9]. In order to do

some further calculations of Rh(2 wt.%)/CeO2 catalyst, adsorbed and desorbed gas volumes with average

pore volumes were measured at different pressure conditions. To determine the effects of different pressures

and average pore diameter on adsorbed and desorbed gas volumes, surface measurements data were analysed.

From the catalyst surface studies, determined external and micropore surface areas of catalyst were 117.956

and 3.4219 m2/gr, respectively. Diameter range of catalyst was 17 A-3000 A and thickness range of catalyst

was 3.3 A-5 A[19].

Adsorbed/desorbed N2 volumes and cumulative and incremental pore volumes were drawn against average

pore diameters, absolute and relative pressures in figures 2 to 5.Absolute pressures and quantity of adsorbed

gas volume against relative pressures were given in fig.2. Absolute pressure is increasing linearly from 100 to

750 mmHg and quantity of adsorbed gas is leveling off upto relative pressure value of 0.8 and then is

increasing exponentially to higher values with increments in relative pressures upto 1. Adsorbed and

desorbed quantity of N2 within catalyst was presented against relative pressure on fig.3. Adsorbed/desorbed

quantity of gas is slightly increased from 0 upto 0.6 value of relative pressure. Adsorption and desorption

curves were merged in the same range of pressure. Adsorption and desorption curves of N2 were

proportionally increased and separated from 70 upto 175 gr/cm3 within relative pressures(p/p) range of 0.6 to

1.0. Cumulative and incremental pore volumes against average pore diameters were given in fig.4.

Cumulative pore volume distribution is inversly proportional with average pore diameter in the range of 0 to

2000 Aº. Cumulative pore volumes are shaply decreasing from 0.3 to 0.05 cm3/gr within 0 to 500 Aº average

pore diameter range. Cumulative and incremental pore volumes are leveling off in the range of 500 to 2000 Aº

of average pore diameter. Incremental pore volumes have smaller values in the range of 0 to 0.02 cm3/gr.

Incremental and cumulative pore volumes curves are merging at average pore diameters in the range of 1750

to 2000 Aº [19].

Quantity of adsorbed and statistical thickness of catalyst against relative pressure was drawn in figure 5. The

quantity of adsorbed gas was in the range of 20 to 80 cm3/gr against realtive pressure range of 0 to 0.8. When

relative pressure was increased, the quantity of adsorbed gas was also increased. Statistical thickness of the

ctalyst was slightly increased from 2 to 8 Aº with relative pressures values of 0 to 0.65. As seen in fig. 5,

statistical thickness of catalyst and quantity of adsorbed N2 was increasing linearly with relative pressures.

As a result of reaction studies, carbon percentage of remainder catalyst (Rh(2 wt.%)/CeO2) of autochem

equipment was 0.272% (0.3%) on the basis of TOC analysis. As a consequence of reaction studies within

reference unit reactor, carbon percentage of remainder catalyst was 2.957% (3%). As a result, carbon

percentage of remainder catalyst within reference unit reactor was 10 times higher than carbon percentage of

remainder catalyst from autochem reactor. By consideration of this fact, catalyst may be used with longer time

on stream in microactivity reference unit reactor. In accordance with this obtained results, carbon formation

rates on catalyst surfaces of both reactors have seen to be very low19.

3.3. Results and discussions of autochem pyrex glass reactor

In completed experiments of TPR, prepared new Rh(2wt.%)/CeO2 catalyst was reduced completely within

autochem equipment at 280C within first 75 minutes (figure 6). TPR experiments with accompaniment of

cold trap were realized by setting up the system to 500C, initially(fig. 6). In conducted TPD experiment,

desorption procedure of Rh(2 wt.%)/CeO2catalyst was realized with pure argon gas by adjusting system to

700C, initially(figure 7). TPR experiments were completed approximately within 2 hours and TPD

experiments were completed approximately with in four hours19.

When Rh(NO3)3.H2O commercial solution was added into diluted CeO2 solution, Rh2O3 and following

components may be formed :

2Rh(NO3)3.H2O→ Rh2O3 . 2H2O + 3NO2 + 3NO3 (9)

When Rh(NO3)3.H2O salt was calcined at 400C, Rh2O3 may be formed as follow:



8 Menderes LEVENT

2Rh2O3. H2O nCalcinatio RhO + RhO2 + Rh2O3 + 2H2O (10)

In accompaniment of carbon monoxide and hydrogen, RhO, RhO2 and Rh2O3 may be reduced according to

following possible reactions :

RhO + CO → Rh + CO2 and RhO + H2 → Rh + H2O (11)

RhO2 + 2CO → Rh + 2CO2 and RhO2 + 2H2 → Rh + 2H2O (12)

Rh2O3 + 3CO → 2Rh + 3CO2 and Rh2O3 + 3H2 → 2Rh + 3H2O (13)

In addition that CeO2 with accompaniment of H2 and CO may be converted (reduced) at higher temperatures

according to following reactions:

CeO2 + 2CO → Ce+ 2CO2 (14)

2 CeO2 + H2 → Ce2O3 + H2O (15)

As seen clearly in these reactions, a certain quantity of CeO2 at higher temperatures was converted to another

products(CO2, H2O, Ce2O3, etc.) which were proportional to these converted percentages. So that proportional

decreases were occurred on catalyst surface areas. This case will effects negatively the activities of CeO2

based catalysts, definetly19.

Time dependent curves of different feed flowrates of standart gas mixture were obtained(see figure 8). When

initial set flowrate of standart gas was decreased step by step, MS signal levels related to each gas were also

decreased, gradually. Thus, we may say current intensity of each signal of mass spectrophotometry was

proportional with step by step changes in feed flowrates of standart gas mixtures19.

Automatically, by increasing temperature step by step from 25C to 200C, signal levels of MS equipment

were determined for each component of standart gas mixture which were fed through pyrex glass reactor of

autochem equipment. MS signal levels of standart gas mixture (contained CO, CH4, CO2, H2) against time

were drawn in Figure 9. As seen on this graph, signal levels against time were become

constant,approximately, for all exit gases(CH4,CO2, H2, CO and H2O) of autochem reactor system. The

consistency of signals related to standart gas mixture was an important evidence to produce accurate results

during the reaction19.

Reduction process of catalyst was carried out with accompaniment of hydrogen (H2) gas at 400C for a

duration of 45 minutes. According to conducted TPR and TPD experiments, ceria dioxide (CeO2) was reduced

with a ratio of 30.1% (percentage of CeO2 conversion) around 500C-600C temperatures in autochem

equipment. Because of this reduction ratio and some sintering, we may say, some losses in expound ratios

were occured in surface area of ceria dioxide. In fact, to study with ceria dioxide support material will notbe

convenient at very high temperatures(600-800C)(see figure 10). However, CeO2 which was prepared by hard

template method has very large surface area. Therefore, CeO2 was used as a support material in preparation of

a few catalysts wide spreadly in catalyst and chemical reaction laboratories of NIC, recently10,19. On

assumption that Al2O3 has used with this Rh based catalyst as support material, sintering and decomposition

of support material might be found around zero percentage withinan operational temperature range of 400-

680C upto 800C 19.

Graphs of catalyst testing and reaction studies of autochem system were presented on figures 6-1119.A

graph of time – MS signals and temperature related to reaction studies within autochem equipment have

presented on figure 10. As seen on this graph, temperature was increased linearly from 200C to 800C.

Methane and carbon dioxide compositions were reduced, continously as to a known value, but hydrogen, rose

during a known time period, then decreased evident, because, decomposition rate in surface area of CeO2 is

effective at higher temperatures above 500C. Carbon monoxide ratio was increased significantly and water

ratio was increased slightly and correspondingly. The greatest increase in exit gas composition of reactor were

found, in carbon monoxide and hydrogen quantitiesat a temperature range of 200-800C. According to graph

of figure 10, H2 quantity was increased, in first portionand then,it was reached to a maximum value, gradually,

around 600C. Then, it was reduced gradually to a stable value and finallyit has become constant(see figure

10), because reduction in CeO2 surface was occurred at temperatures over 500C. Reduction percentage in



9 Menderes LEVENT

surface of CeO2 support at 600C was around 30.1 % .When temperature has increased to 800 C in autochem

equipment, decomposition ratio in CeO2 surface area was become much higher and significant. Therefore,

surface area of catalyst(121.378 m2/gr) was reduced to below 84 m

2/gr araound 600 C. As a result of this

fact(figure 10), H2 percentages in exit gas composition were reduced, significantly and CO percentagesin exit

composition were incereased to higher values(see fig.10). Additionally, lower H2O quantities have

determined in the exit gas composition. H2O quantities were started to produce from these low values to

slightly higher values and then, produced H2O values were became constant, steadly during the reaction(see

fig.10).In order to produce higher hydrogen percentages at temperatures more than 600C, CeO2 catalyst

support must be replaced with more stable Al2O3 support19.

Then, other reaction products (CO and CO2)of autochem equipment were observed with an IR equipment(see

Figure 11). On this graph, CO quantity was increased parabolically to a stable value, but then CO values

continously increased,approximately to 15% at 550 C, and then, CO ratios were became slightly leveling off.

IR detector has a capability to measure CO up to a maximum value of 30. It has a capacity to measure carbon

dioxide in all digital intervals. Reaction measurements with autochem equipment were conducted in

temperature range of 200 - 800C. Each time, by making 10C increments in temperature, CO and CO2 values

were observed. In exit of autochem equipment, CO2 values were decreased gradually with increasing reactor

temperatures from 400 up to 800C.

3.4. Results and discussions of microactivity reference unit reactor

According to the conducted experimenal studies within reference unit reactor and autochem glass reactor, the

prepared Rh(2 wt.%)/CeO2 catalyst has shown good activity values at temperature range of 500C-680C and

at different feed flowrates conditions. With 20 ml/min CH4+CO2 mixture and 80 ml/min He feed flowrates at

500C , a small quantity of hydrogen has been detected at the reactor exit gas composition. Other three

products(H2O, CH4 and CO2) were also detected in exit gas composition. As far as we understand here, who

maybe able to say, defined reaction is not taking place at higher ratios over Rh(2 wt.%)/CeO2 catalyst until

temperature is reached to 500C 19.

In conducted dry reforming of methane and carbon dioxide reaction with 50% CH4+CO2 and 50% He feed

flowrates over Rh(2 wt.%)/CeO2 catalyst at 680C, measured quantity of H2 was 20.19%,measured quantities

of other gases H2O and CO were 2.54 and 24.49%, respectively. Determined quantities of CO2 and CH4 were,

also, 4.70 and 6.36%, respectively,at the exit gas composition(see fig.12).

In dry reforming of methane and carbon dioxide reaction at 680C over Rh(2wt.%)/CeO2 catalyst with 100%

CH4+CO2(with 20 ml/min CH4+CO2 and 0 ml/min He), measured quantity of H2 was 29.05% and quantities

of other gases were H2O: 3.99%, CO:37.89%, CH4: 11.90% and CO2: 8.76%, in exit gas composition. In case

of a small stream of He in reactor feed with CH4+CO2 mixture, lower quantities of H2 were found in exit gas

compositions. When switching off He flowrate in reactor feed, approximately, an 8.86% increment in H2

quantity was observed, inexit gas composition. Incerement ratio in H2O vapour quantity was 1.45%,

approximately,in exit gas composition. Increment in CO ratio, was also,13.4%. Increment in CO2 quantity was

4.06%, approximately and increment in CH4 quantity was 5.54%. In the latest experiments as seen that higher

CH4 and CO2 conversions and H2 production rates(29.05%, etc.),were realised, with Rh(2wt.%)/CeO2 catalyst

when operational temperatures increased to above 650ºC, but operational temperatures of the experimental

setup were restricted to 700 ºC, so any kinetic measurements above 680 ºC were not become possible in this

study(see Figures 12-13)[19].

Reactor exit gas compositions against temperature was presented in figure 12. As seen on this graph,

hydrogen compositions were increased with temperature in the studied temperature range. And also, lower

ratios of water vapour were seen at the exit of reactor. The highest CO quantity was found at the reactor exit

and it was found approximately equal to the total composition of H2 and H2O. Gas compositions of CH4 and

CO2 in figure 12 were decreased, gradually. This result is a valuable indication which shows that newly

synthesised catalyst has a good activity. According to the completed measurements, we understand that

conversion of CH4 and CO2 are realized, significantly during the reaction(see Fig. 12).In conducted reaction



10 Menderes LEVENT

studies, it has been observed that activity of Rh(2wt.%)/CeO2 catalyst was much better than the activity of

other different CuO/CeO2 catalysts.

Product compositions of dry reforming reaction within microactivity reference unit reactor at 680C

temperature and different feed flowrates were given in Figure 13. In this graph, hydrogen ratio was 20% in the

reactor exit gas composition, when feed gas flowrates have increased gradually from 20 ml/min to 80 ml/min,

slight decreases in hydrogen ratios(4%) have recorded in exit gas composition of the reactor. Similarly, the

lowest ratios of water vapour were found, but, with increment in feed flowrates, a slight increase(1%) was

seen in formed water vapour ratios. With some increases in feed flowrate from 40 to 80 ml/min, carbon

monoxide ratio was increased, slightly(4%) and then, it was become constant (28%). As a result, the highest

CO ratio was determined among other gases at the exit of the reactor. When gradual increases in the feed flow

rates were realised, methane and carbon dioxide ratios were also increased, proportionally, within the exit gas

copositions. On the basis of these results, we may say, by keeping temperature constant at 680C and making

some increases in feed flowrates have not increased, hydrogen yields in the exit gas composition. An increase

in supply feed rate was lowered the retention time of reactants in the reactor, conversely, some decreases in

hydrogen ratios and other product yields were observed in outlet gas compositions[19].

According to kinetic measurements of dry reforming of CH4 and CO2 at different experimental conditions

some kinetic parameters of reaction were calculated(see Table 1). On the basis of different inlet feed

flowrates, different catalyst loads(50-150 mgs.), and different temperatures, some kinetic parameters were

computed for CH4, CO2 consumptions and H2 formation ratios. Activation energies of dry reforming of

CH4+CO2 reaction in temperature range of 550-680C for consumptions of CH4 and CO2 were determined as

89,4424 kJ/mol and 61.9309 kJ/mol, respectively(fig.14). Because of these lower values of activation energies

and from literature review and some kinetic analysis of this study, perhaps we may say that dry reforming of

CH4 and CO2 reaction is chemical reaction controlled and is first order on the basis of methane and carbon

dioxide consumptions and hydrogen formation rates. The inversely proportional curve of 1/T-lnk graph of

above recation in fig. 14 may shows that diffusion resistance has less effect on the reaction rate.The

calculated activation energies and activation energies of similar studies in literature have good agreement and

proved to be a good fit of the results[2,20,21].

Table 1 . Determined some kinetic parameters of CH4 and CO2 dry reforming reaction

T(O

K) XCH4 XCO2 kCH4

(1/dak)

kCO2

(1/dak)

RCH4

(mol/gr.min)

RCO2

(mol/gr.min)

ECH4

(kJ/mol)

ECO2

(kJ/mol)

823.15 0.1414 0.2187 34.5615 56.2665 0.8979 1.3705 89.4424 61.9309

873.15 0.3565 0.4654 95.0664 117.2145 2.1809 2.7924

923.15 0.5682 0.6668 164.1260 167.3769 3.3453 3.8551

953.15 0.6820 0.7651 206.1195 194.4659 3.9316 4.3417

4. Conclusions

Dry reforming studies of CH4 with CO2 was carried out under different experimental conditions within both

microactivity reference unit reactor and autochem glass reactor. In studied temperature range, although we did

not detect significant quantity of hydrogen by GC within product during studies over different types of

CuO/CeO2 catalysts within reference unit reactor, but, a small quantity of dry reforming reaction was took

place beginning from a temperature of 500C. Reaction studies with autochem equipment have cofirmed this

fact, but, different types CuO/CeO2 catalysts have not shown appropriate activities for this reaction. Because

of lower ratios of produced hydrogen were always less than 5% at the exit gas composition of the reference

unit reactor, who perhaps be said, convenient hydrogen ratios could not be found with above types CuO/CeO2

catalysts, at studied temperature range from 400C up to 680C. In fact, produced H2 ratios were realized up



11 Menderes LEVENT

to 5% in the same temperature range with different types of CuO/CeO2 catalysts in autochem equipment

during reaction studies.

When CeO2 catalyst support is compared with Al2O3 support material, for temperatures higher than 600C,

CeO2 support material is not capable of a good resistance. Therefore, a certain proportion of CeO2 is starting

to decay from 600C up to further temperatures. According to our calculations, 30.1 %, CeO2 was reduced

approximately at 650C(fig.10). Due to this sintering, surface area of CeO2 was decreased in prepared

catalyst, this effect has caused some losses in hydrogen yields which is proportional to sintering

percentages. However, with using the latest Rh(2wt.%)/CeO2 catalyst for the purposed reaction,better activity

values were observed. The activity tests of catalyst and reaction studies were carried out at

intermediate(450C-600C) and at higher temperatures (600C-800C). The catalyst conditioning and reaction

studies were carried out with 50 - 150 mgs. of Rh(2wt.%)/CeO2 catalysts samples, within both reference unit

reactor and autochem glass reactor with accompaniment of the mass sphectrophotometry. For the intended

reaction with prepared Rh(2wt.%)/CeO2 new catalyst, higher hidrojen and synthesis gas compositions were

determined at the exit of both reactors.Contribution of Rh(2wt.%)/CeO2 catalyst on produced hydrogen and

synthesis gas was investigated, the obtained hydrogen and synthesis gas ratios were high enough in studied

temperature range and thus, the activity of new catalyst was found to be better for the purposed reaction. In

the case of using Al2O3 as a support material for Rh catalyst in different experimental set up with option of

higher temperature operations, then, higher ratios of synthesis gas will be produced, definetly. Obtained

activtion energies show that CH4+CO2 reaction is first order and chemical reaction step has some influences

on the overal reaction rate.

5. Acknowledgement

Author wishes to thank Prof. Levec, head of the laboratory, for the given opportunity to work in his laboratory

and for his valuable advices during experimental measurements. He also thanks other members of the

laboratory for their help during experimental work and Turkish Scientific Research Council (TUBITAK) for

providing scholarship for his work at NIC.

6. Nomenclature

NIC : Slovenian national institute of chemistry

TPR : temperature programmed reduction

TPD: temperature programmed desorption

WGSR: water gas shift reaction

MS : mass spectrophotometry

FTIR : fourier transform infrared spectrophotometry

XRD : x-ray difractrometry

TOC: temperature oxidation carbon analyser

GC : gas chromatography

TCD : thermal conductivity detector

R : gas constant ( 8.314 J/mol.K)

T: absolute temperature (K)

CCH4 : concentration of methane (mol/liter)

W : weight of used catalyst (gr) '

4CHR : reaction rate of methane consumption (mol/gr.cata.min.)

0

4CHF : molar flowrate of methane (mol/min.)



12 Menderes LEVENT

XCH4 : conversion of methane (in

outin

F

FF )

PCH4 : partial pressure of methane (bar)

k : reaction velocity consatnt (1/min)

A : frequency factor of Arrhenius equation

EA : activation energy of consumed methane (kJ/mol)

7. References 1 K.Tomishige, O.Yamazaki, Y. Chen, K.Yokoyama, X. Li, K.Fujimoto, Development of ultra-stable Ni catalysts for

CO2 reforming of methane, Catalysis Today 45 (1998)35-39.

2 S. Wangand G.Q. Lu, G.Q. Max, A Comprehensive Study on Carbon Dioxide Reforming of Methane over Ni/-

Al2O3 Catalysts, Ind.Eng.Chem.Res. 38(1999)2615-2625.

3 U.L. Portugal, A.C.S.F. Santos, S. Damyanova, C.M.P. Marques, J.M.C. Bueno, CO2 reforming of CH4 over Rh-

containing catalysts, Journal of Molecular Catalysis, A : Chemical 184 (2002)311- 322.

4 M.M.V.M. Souza and M. Schamal, Methane conversion to synthesis gas by partial oxidation and CO2 reforming

over supported platinum catalysts, Catalysis Letters 91(1-2) (2003)11-17.

5 X.E. Verykios, Mechanistic aspects of the reaction of CO2 reformingof methane over Rh/Al2O3 catalyst, Applied

Catalysis A: General 255(2003)101-111.

6 X. Chen, K. Honda, Z.G. Zhang, A comprehensive comparison of CH4-CO2 reforming activities of NiO/Al2O3

catalyst under fixed and fluidized bed operations, Applied Catalysis A:General 288 (2005)86-97.

7 F. Kleitz, K. Tae-Wan and R. Ryoo,Design of Mesoporous Silica at Low Acid Concentrationsin Triblock

Copolymer-Butanol-Water Systems, Bull. Korean Chem. Soc. 26 (11)(2005)1653-1658.

8 M.M.B. Quiroga and A.E.C. Luna, Kinetik Analysis of Rate Data for Dry Reforming of Methane,

Ind.Eng.Chem.Res. 46 (2007)5265-5270.

9 M. Nagai, K. Nakahira, Y. Ozawa, Y. Namiki, Y. Suzuki, CO2 reforming of methane on Rh/Al2O3 catalyst,

Chemical Engineering Science 62 (2007)4998-5000.

10 A. Donazzi, A. Beretta, G. Groppi, P. Forzatti, Catalytic partial oxidation of methane over a 4% Rh/α-Al2O3

catalyst, Part II : Role of CO2 reforming, Journal of Catalysis 255 (2008)259-268.

11 J.M. Li, F.Y. Huang, W.Z. Weng, X.Q. Pei, C.R. Luo, H.Q. Lin, C.J. Huang, H.L. Wan, Effects of Rh loading on

the performance of Rh/Al2O3 for methane partial oxidation to synthesis gas, Catalysis Today 131 (2008)179-187.

12 P. Djinovic, J. Batista, J. Levec, A. Pintar, Comparison of water-gas shift reaction activity and long term stability on

nanostructured CuO-CeO2 catalysts prepared by hard template and co-precipitation methods, Applied Catalysis A:

General 364(1-2) (2009)156-165.

13 M.M.Barroso-Quiroga, A.E. Castro-Luna, Catalytic activity and effect of modifiers on Ni-based catalysts for the dry

reforming of methane, International Journal of Hydrogen Energy 35(11) (2010)6052-6056.

14 N.E. McGuire, N.P. Sullivan,O. Deutschmann, H. Zhu,K..R.J. Robert, Dry reforming of methane in a stagnation-

flow reactor using Rh supported on strontium-substituted hexaaluminate, Applied Catalysis A: General 394(1-2)

(2011) 257-265.

15 N. Wang, W. Chu, T. Zhang, X.S. Zhao, Manganese promoting effects on the Co–Ce–Zr–Ox nano catalysts for

methane dry reforming with carbon dioxide to hydrogen and carbon monoxide, Chemical Engineering Journal

170(2-3) (2011)457-463.

16 R.Shang, X. Guo, S. Mu, Y. Wang, G. Jin, H. Kosslick,A. Schulz,X.Y. Guo, Carbon dioxide reforming of methane

to synthesis gas over Ni/Si3N4 catalysts, International Journal of Hydrogen Energy 36(8) (2011)4900-4907.

17 P.Djinovic,I.G.O. Crnivec, J. Batista, J. Levec, A. Pintar, Catalytic syngas production from greenhouse gasses:

Performance comparison of Ru-Al2O3 and Rh-CeO2 catalysts, Chemical Engineering and Processing: Process

Intensification 50(10)(2011)1054-1062.

18 P. Djinovic, J. Batista, A. Pintar, Efficient catalytic abatement of greenhouse gases: Methane reforming with CO2

using a novel and thermally stable Rh–CeO2 catalyst, International Journal of Hydrogen Energy37 (3)(2012)2699-

2707.

19 M. Levent, Dry Reforming of Methane and Carbon Dioxide over A Rhodium Dioxide-Ceria Dioxide Catalyst,

Research Report, Submmited to TÜBİTAK (September, 2009).

[20] M. Levent, Dry Reforming of Methane and Carbon Dioxide over a Rh(2wt.%)/CeO2 Catalyst, ISITES2014, (2nd.

International Symp.on Innov.Tech. in Eng. and Sci.), June 18-20, 2014, Karabük University, Karabük, Turkey.

http://www.sciencedirect.com/science/article/pii/S0360319909020011


http://www.sciencedirect.com/science/journal/0926860X







http://www.sciencedirect.com/science/article/pii/S036031991102489X

http://www.sciencedirect.com/science/article/pii/S036031991102489X



13 Menderes LEVENT

[21] B.V.Ayodele, M.R.Khan, C.K.Cheng, Syngas production from CO2 reforming of methane over ceria supported

cobalt catalyst: Effect of reactant partial pressure, J. of Natural Gas Science and Eng. 27(2015)1016-1023.

Figure 1. Position 2(Theta)(Copper(Cu))-Counts graph of XRD analysis obtained from X-ray powder

diffractometer equipment for Rh (2 wt. %)/CeO2 catalyst.

0,0 0,4 0,8 1,2

0

300

600

Qu

anti

ty A

dso

rbed

N2 (

cm3 /g

r),

Ab

solu

te P

ress

ure

(m

mH

g)

Relative Pressure (p/po)

Absolute Pressure

Quantity Adsorbed

Figure 2. Isotherm of adsorbed N2 quantity and absolute pressure against relative pressure(p/p

o).

Position [°2Theta] (Copper (Cu))

20 30 40 50 60 70 80

Counts

0

500

1000

1500

(111)

(200)

(220)

(311)

(222) (400)

(331)

(420)



14 Menderes LEVENT

0,0 0,2 0,4 0,6 0,8 1,0

0

50

100

150

200

Ads

orbe

d Q

uant

ity o

f Gas

(gr/c

m3 )

Relative Pressure, (p/po)

Adsorption

Desorption

Desorp.

CurveAdsorp.

Curve

Figure 3. Adsorbed and desorbed quantity of N2 over Rh(2wt.%)/CeO2 catalyst against relative pressure

(p/po).

0 1000 2000

0,0

0,1

0,2

0,3

Incr

emen

tal a

nd

Cu

mu

lati

ve

Po

re V

olu

mes

(cm

3 /gr)

)

Average Pore Diameter (Ao)

Incremental Pore Volume

Cumulative Pore Volume

Figure 4. Cumulative and incremental pore volume against average pore diameter of Rh(2wt.%)/CeO2

catalyst against (diameter rangeof pores = 17 Ao-3000 A

o).



15 Menderes LEVENT

0,0 0,2 0,4 0,6 0,8

0

20

40

60

80

Qu

anti

ty A

dso

rbed

(cm

3 /gr)

Sta

tist

ical

Th

ickn

ess

(Ao)

Relative Pressure (p/po)

Statistical Thickness

Quantity Adsorbed

Figure 5. Statistical thickness of Rh(2wt.%)/CeO2 catalyst and quantity of adsorbed N2 gas against relative

pressure(p/po)(thickness range of catalyst = 3.3 – 5.0 A

o)

0 100 200 300 400 5000.59

0.60

0.61

0.62

0.63

0.64

0.65

TC

D s

ign

al,

V

Temperature, ° C

2% Rh/CeO2

VH2

=28.91 ml/g (STP)

Figure 6. TPR analysis at different temperatures against TCD signal for Rh(2wt.%)/CeO2 catalyst with

autochem equipment.



16 Menderes LEVENT

0 100 200 300 400 500 600 700

-0.5235

-0.5230

-0.5225

-0.5220

-0.5215

-0.5210

-0.5205

-0.5200

-0.5195

VH2

=3.02 ml/g (STP)

TC

D s

ign

al,

V

Temperature,° C

2% Rh/CeO2 TPD

Figure 7. TPD analysis at different temperatures against TCD signal for Rh( 2 wt.%)/CeO2 catalyst with

autochem equipment.

0 1000 2000 3000 4000

1E-12

1E-11

1E-10

1E-9

1E-8

1E-7

MS

sig

nal,

A

Time, s

(CO)

(CO2)

(H2)

(H2O)

(CH4)

p7013

Figure 8. MS signal of different feed flowrates of standart gas against time over Rh( 2 wt.%)/CeO2 catalyst.



17 Menderes LEVENT

0 500 1000 1500 2000

10-9

10-8

10-7

10-6

0

50

100

150

200

250

MS

sig

nal,

A

Time, s

(H2)

(CO2)

(CO)

(H2O)

(CH4)

p7011

Tem

pera

ture

, ° C

Figure 9. MS signal of standart gas mixtures against time at lower temperatures(35-200 C) with autochem

equipment.

0 2000 4000 6000 8000

1E-10

1E-9

1E-8

1E-7

200

300

400

500

600

700

800

MS

sig

nal, A

Time, s

B

D

L

M

N

p7012

Tem

pera

ture

, °

C

Figure 10. MS signal against time on stream at higher temperatures(200-800C) over Rh( 2 wt.%)/CeO2

catalyst during dry reforming of methane and carbon dioxide reaction with micromeritics

autochem equipment.



18 Menderes LEVENT

300 600 900

0

10

20

30

Car

bon

diox

ide

and

Car

bon

mon

oxid

e

Rea

ding

s on

Bin

os-1

001-

IR

Temperature (0C)

CO

CO2

Figure 11. Measured CO and CO2 compositions on IR equipmentagainst temperature during the CH4+CO2

reaction with micromeritics autochem system.

550 600 650

0

10

20

30

Exi

t G

as

Co

mp

osi

tion

(%

)

Temperature (0C)

CO2

H2O

H2

CH4

CO

Figure 12. Gas compositionpercentage(%) at the exit of reactor against different temperatures during

CH4+CO2 reaction with microactivity reference unit reactor (FCH4+CO2 = 20 ml/min / FHe = 20

ml/min).



19 Menderes LEVENT

20 40 60 80

0

10

20

30G

as C

ompo

sitio

n %

at t

he E

xit o

f Rea

ctor

Reactor Feed Flowrate (ml/dk)

CO2

H2O

H2

CH4

CO

Figure 13. Exit gas composition percentage(%) of reactor against different feed flowrates of mixture (FHe = 20

ml/min) for CH4+CO2 reaction with microactivity reference unit reactor at temperature of 680 C.

0,00105 0,00112 0,00119

4,2

4,8

5,4

lnk

(dk-1

)

1/T (K-1)

Figure 14. 1/T- lnk plot of consumed CH4 during CH4+CO2 reaction (determined activation energy, EA is

89,4424 kJ/mol for temperature range of 550-680C).

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