DOI:10.30919/esee8c201

ES Energy & Environment, 2019, 3, 68-73

Published online: 26 Jan 2019

Received 22 Nov 2018, Accepted 25 Jan 2019

High-pressure catalytic Kinetics of CO2 Reforming of Methane Over Highly Stable NiCo/SBA-15 Catalyst

 Hao Wu1, Yajin Li1, Huimin Liu1,2* and Dehua He1*

1Innovative Catalysis Program, Key Laboratory of Organic Optoelectronics and Molecular Engineering of Ministry of Education, Department of Chemistry, Tsinghua University, Beijing 100084, China

2School of Chemical and Biomolecular Engineering,The University of Sydney, NSW 2006, Australia

*E-mail: [email protected]; [email protected]

Abstract:

Investigating the kinetic behaviors of catalystsinthe reaction of CO2 reforming of CH4 (CRM)under industrially practical pressures is of great significance for designing stable catalysts for its industrialization.This study explores the kinetic behavior of 4.5Ni0.5Co/SBA-15-CD, a stable catalyst for pressurized CRM (2000 kPa), at a continuous flow-type fixed-bedquartz tube lining-Inconel tubular reactorunder kinetically controlled conditions. The kinetic measurements suggested that the forward reaction rates were monotonically increasing with the partial pressures of CH4(200 – 400 kPa), and independent of the partial pressures of CO2(100 – 300 kPa) over 4.5Ni0.5Co/SBA-15 at 2000 kPa total pressure and 620-660 oC. The trace Co enriched on the outmostsurface of NiCo particles of 4.5Ni0.5Co/SBA-15 facilitated the adsorption of co-reactant, and the decomposition of methane was the sole kinetically relevant step.Apparent activation energy of CRM reaction at high pressure measured on 4.5Ni0.5Co/SBA-15was 106.5kJmol-1 at total pressure of 2000 kPa.

KeywordsCO2 reforming of methane; Ni-Co catalyst; High pressure; Kinetics

1. Introduction

The reaction of CO2 reforming of methane (CRM) is important for the conversion of the two greenhouse gases, CO2 and CH4, into syngas (the mixture of CO and H2), a valuable feedstock for the downstream production of clean fuels by the approach ofFischer-Tropsch Synthesis (FTS). Ni has been investigated as an active metal for the CRM reaction, but Ni-based catalysts also sufferfrom gradualdeactivationduring the CRM due to carbon deposition and metal sintering.1-3 Many researchers have been devoting a lot of effort tryingto enhance the catalytic performance of Ni-based catalysts, including the support type and doping,4-8 modification of Ni metal,9-10 improvement of support and catalyst preparation methods,11-12 metal-support interaction13-14 and etc, and many remarkble results have also been achieved.On the other hand, from the industrial practical point of view, it is economic to perform pressurized CRM due to the following several reasons. (1) The exploitation, storage and transportation of natural gas(with the main component as methane), as well as the synthesis of chemicals via FTS are mostly carried out at high pressures. Then the pressure-bearing, CO-rich synthesis gas (H2/CO<1) obtained by the pressurized CRM reaction could be used directly in industrial FTS processes.15-16 (2) The reactor used for pressurized CRM requires less volume and space and benefits for energy saving.17-18 (3) Pressurized H2 (over 1 MPa) is usually required by energy consumers, which makes it not economically desirable to compress large quantities of H2 gas frequently.19 Therefore, studying pressurized CRM is one of the important research directions.Nevertheless, most of the reported researcheswere focused on CRMthat carried out under atmospheric pressure,20-23 while the researches onhigh pressure CRM over Ni catalysts were relatively less reported. Aika et al.24-25 and Fujimoto et al.26-27 devoted a lot of effort to the studies on high pressure (1.0 – 2.0 MPa)CRM. Recently, we also reported a Co-modified Ni catalyst showed pretty good performance in pressurized CRM reaction.28

Besidesthe researches on catalysts, investigating catalyst kinetic behaviours is a promising approach for providing insights for the development of stable catalyst. There have been multiple kinetic studies in atmospheric CRM, and different types of kinetic models were achieved.Maier et al. investigated the kinetics of CRM over Ir/Al2O3 in the range of 700-850 oC and a first order model was obtained by numerically fitting the experimental data with rate equations.29 Nguyen et al. found that over Ni0/La2O3, the reaction order was constant in terms of CH4 whereas was highly dependent on the concentration/pressure of CO2.30 While on the other hand, in spite of some contradictions on reactant activation and rate-determiningstep, Langmuir-Hinshelwood model have been suggested by several kinetic studies.31 For example, Bhatia et al. studied the reactionkinetics over Ni-Co bimetallic catalyst at different reactantpartial pressures (0.045-0.36 MPa), anda kinetic model,the Langmuir-Hinshelwood model, was proposed that the adsorption and cracking of methane on metallic Ni particleswas the rate-determiningstep, in whichthe reaction between CO2or its derived carbonate species withcarbon existed at the interface of metal-carbon produced CO and removed the carbon deposited on the active metallic catalyst surface.31 The Langmuir-Hinshelwood kinetic modelwas also proved on Rh/La2O3 by Cornaglia et al.32, on Co/Pr2O3 by Ayodele et al33 andon Ni/La/Al2O3 by Olsbye et al.34.On the contrary, Osaki et al. suggested that over Ni based catalysts, such as Ni/MgO, Ni/Al2O3 and Ni/SiO2, the rate-determining step in CRM was the reaction betweenCHx, adsand CO (or Oads).35 Another type of Langmuir-Hinshelwood kineticsmodel was regarded as a better representative model for Co/La2O3 catalyst in CRM, in which both CH4 and CO2were associatively adsorbedvia a dual-site model followed by bimolecular surfacereaction.36

To the best of our knowledge, the kinetic behaviour of CRM over Ni-Co catalyst under industrial practical pressure conditions has not been reported in detail. Therefore, from the industrialization point of view, it will be of great significance to study the kinetic behaviour of CRMNi-Co catalystat pressurized conditions.Our group previous studies revealed that 4.5Ni0.5Co/SBA-15-CDcatalyst prepared bythe β-CD modified impregnation method has excellent activity and stability both in atmospheric and pressurized CRM reaction(2000 kPa, V(CH4)/V(CO2)=1:1, GHSV=3.0×104mL/g/h).10,28 Hence, in this paper, 4.5Ni0.5Co/SBA-15-CD is used as probe catalyst for studying pressurized CRM under kinetically controlled conditions. The effects of reaction conditions, especially reaction pressure,is explored and verified.

2. Experimental section

The reagents,such as Ni(NO3)2·6H2O, Co(NO3)2·6H2O, tetraethyl orthosilicate, β-cyclodextrin (β-CD), hydrochloric acid (HCl, 36~38 %), were used for preparing the catalyst, and the detailed manufacturer sources of the reagents could be referencedfrom our previous paper.28 The standard gases with different CH4/CO2 ratios(Ar gas balance) were purchased from Beijing Hua Tong Jing Ke gas Co., Ltd.

The catalyst used for the pressurized CRM reaction, 4.5Ni0.5Co/SBA-15-CD, was preparedwith the β-CD modified impregnation method,37 and the preparation procedure can be seen in our previous work.28 The total metal loading (Ni and Co) was theoretically kept as 5 %.

The physico-chemical properties of 4.5Ni0.5Co/SBA-15-CD were characterized by N2 adsorption-desorption isotherm,X-ray diffraction,Inductively coupled plasma-atomic emissionspectroscopy,X-ray photoelectronspectroscopy, H2-temperature programmed reduction methodsand Transmission electronic microscopy, while the detailed characterization results have been shown in our previous paper. 10, 28

Thekinetic measurementsof CRM reaction over 4.5Ni0.5Co/SBA-15-CD catalyst under the totalpressure of 2000 kPa were conducted at acontinuous flow-type fixed-bed quartz tube lining-Inconel tubular reactor, with schematic diagram of equipment available in our previous paper.28 Before each reaction, gas leakage test was carried out with Ar gas at 2200 kPa to make sure no gas leaking.Before the CRM reaction, the catalyst was reduced in-situ in flowing 5 % H2/Ar (20 mL/min) atatmospheric pressure and 700 oC for 1 h.The reactant gases were fed into the reactorat a given pressure.All eighttypes of CH4 and CO2mixed gases (Ar gas balance)were served as feed gases in the kinetic measurements, and the detail compositions of each feed gas are listed in Table 1.The flow rate was monitored by mass flow controllers (MFC), and the reaction temperature was detected by inserting a thermocouple (TC) to the catalyst bed. All the operating proceduresof pressurized CRM reaction, products analysis and the conversion and selectivity calculation methods are same as our previous work.28

Table 1 Detail compositions of each standard gas.

Number

Composition (mol%)

CH4

CO2

Ar

1

50

50

0

2

10

10

80

3

5

10

85

4

15

10

75

5

20

10

70

6

10

5

85

7

10

15

75

8

10

20

70

3.1 Exclusion of internal and external transport artifacts for kinetic measurements

The stable performance of 4.5Ni0.5Co/SBA-15-CD catalyst under pressurized CRM (2000 kPa, V(CH4)/V(CO2)=1:1, GHSV=3.0×104 mL/g/h)has been verified inour previous work.28 Before the kinetic measurements, the methods of changing the flow rates of feed gas and the particle sizes of the catalyst are usually adopted to eliminate the external and internal transport artifacts. Therefore, theeffects of flow ratesof feed gas and the catalyst particle sizes on the reaction rate of 4.5Ni0.5Co/SBA-15-CD were checked, and the results are displayedin Fig. 1 and Fig. 2. It is clear that the external transport artifact could be eliminated by adopting the flow rate of feed gasmore than 60 mL/min, and there is no influence of internal transportartifact if the particle size of catalyst is less than about 0.4mm (>40mesh). According to these results, 90 mL/minflow rate of feed gasand 40-60 mesh particle sizeof the catalyst were employed. So, thekinetic measurementsof 4.5Ni0.5Co/SBA-15-CDcatalyst were carried out at kinetically limited conditions: 15mg catalyst diluted with 600 mg quartz, 40-60mesh particle size, 90mL/min total flow rate (total GHSV=3.6×105 mL/g/h), 2000 kPa total pressure and 620-700 oC. The partial pressures of both CH4 and CO2 were kept in the range of 100 – 400 kPa.

Fig. 1 Effect of flow rates on reaction rate of 4.5Ni0.5Co/SBA-15-CD.

Reaction conditions: 660 oC, CO2/CH4/Ar=10/10/80, GHSV=3.6×105mL/g/h, catalyst diluted with 600mg quartz, 2000 kPatotal pressure.

Fig. 2 Effect of particle sizes on reaction rate of 4.5Ni0.5Co/SBA-15-CD.

Reaction conditions: 660 oC, CO2/CH4/Ar=10/10/80, GHSV=3.6×105mL/g/h, catalyst diluted with 600mg quartz, 2000 kPatotal pressure.

3.2 Reaction kinetic studies over 4.5Ni0.5Co catalyst at atotal pressure of 2000 kPa

In order to ensure the reliability of the kinetic measurements, the CH4reaction ratesin pressurized CRM atthe present study were kept at a low level (less than 20 % CH4 conversion). The GHSV was as high as 3.6×105 mL/g/h, so that the net rate measurements were far from the equilibrium.Based on the reaction conditions and the partial pressures of each substance under steady-state reaction, we could estimate the differences between the actual reaction states and the thermodynamic equilibrium states under the reaction conditions, which is called the reaction progress degree η, and itcould be calculated according to the following equation.38-39

where [Pi] is the partial pressure for the reactant/product species i (in units of kPa) inCRM reaction, while [KEQ] is the equilibrium constant for CRM at the operating reaction temperature.

At the present study, ηvalues were controlledin the range from 0.03 to 0.28, so the reactions were far from the equilibrium. The influence of CH4 partial pressures on the pressurizedCRM reaction rate was measured with fixing CO2 partial pressure being200 kPa while adjusting CH4 partial pressure in the range of 200 ~ 400 kPa, under the condition of total pressure 2000 kPa (Ar as balance gas). Similarly, the influence of CO2 partial pressures on the pressurizedCRM reaction rate was measured with fixing CH4 partial pressure being200 kPa while adjusting CO2 partial pressure in the range of 100 ~ 300 kPa, under the condition of total pressure 2000 kPa. The CRM reaction rate determined under the CRMexperimental conditions with different temperatures and different partial pressures of the reactantswas the net reaction rate rn, while the forward reaction rate(rf) could be obtained from net reaction rate(rn) and reverse reaction rate(rr) using the following formula.38-39

Here, the net reaction rate was corrected for approach to reaction equilibrium (η),while η can be obtained from the equilibrium constant and prevalent pressures of reactants and products, and this equation described the observed effect of reactor residence time and CH4 conversion level on the measured CRM rates, according to the research results by Iglesiaetal.38

Based on the obtained forward reaction rate (rf), the effects of the partial pressures of CH4 and CO2 on the forward CH4conversion rate over 4.5Ni0.5Co/SBA-15-CD at 620-660 oC and 2000 kPa total pressure are shown in Fig.3 and Fig.4.

Fig. 3 Effects of CH4 partial pressures on the forward CH4cnversion rate in CRM over4.5Ni0.5Co/SBA-15-CD.

Reaction conditions: GHSV=3.6×105mL/g/h, balance gas Ar, 2000 kPa total pressure.

 

Fig. 4 Effects of CO2 partial pressures on the forward CH4conversion rate in CRM over4.5Ni0.5Co/SBA-15-CD.

Reaction conditions: GHSV=3.6×105mL/g/h, balance gas Ar, 2000 kPa total pressure.

As it is clear fromFig. 3, the forward reaction rates of pressurized CRM were proportional to the partial pressure of CH4(200 – 400 kPa) at reaction temperatures of 620-660 oC over 4.5Ni0.5Co/SBA-15-CD under 2000 kPa total pressure.The proportional relationship was due to the reason that the frequency of CH4 contacted with an active site per unit time was increased as the partial pressure of CH4 increased, which increases the number of effective collisions of CH4, thereby increasing the forward reaction rate. On the other hand, the forward reaction rate of pressurized CRM were independent of CO2partial pressures (100 – 300 kPa)at different temperatures (620 oC ~ 660 oC), as shown in Fig. 4.The independence reaction rate on CO2 partial pressure might be due to the reason that the elementary steps of CO2 adsorption and the surface reaction between the adsorbed species CO2* and CH4 decomposed species CH4-x* were fast steps, which approached the reaction equilibrium, so that the partial pressures of CO2 did not affect the forward reaction rate.These results mentioned above are agreed with the reported kinetics for supported metal catalystsmentioned in the literature, and it was also confirmed that the co-reactant CO2 and the partial pressures of the products CO and H2 had no influence on the forward reaction rate in the CRM reaction.38-43

The side reaction, reverse water-gas shift reaction (RWGS, CO2+H2=CO+H2O) would occurs unavoidably duringCRM reaction. The extent of RWGS equilibrium (ηRWGS)at different temperaturesas a function of the composition of feed gas was calculated with the following equation,38-39

ηRWGS= ([PCO][PH2O])/([PCO2][PH2]KRWGS),

where [KEQRWGS]is the equilibrium constant of RWGS reactionat the operatingreaction temperature,

by assuming the [PH2O] equals to the equilibrium calculated,as shown in Fig.5. Thevalue of ηRWGS closes to unitysuggesting that all the RWGS relevant elementary steps were fast steps. These results clearly indicated that CH4activation was the onlykinetically controlledelementary stepover4.5Ni0.5Co/SBA-15-CD catalysteven underhigh pressures (~2000 kPa). The desorption of hydrogen and CO,as well as the reaction of CH4-x* species with CO2* were fast steps, so that the RWGS would be equilibrated under the present reaction conditions.38

Fig. 5 Extent of RWGS equilibrium at varied reactiontemperatures as a function of feed gas composition.

Reaction conditions: GHSV=3.6×105mL/g/h, Ar gas balance, 2000 kPa total pressure.

Based on the fact that the forward CH4 reaction rate was proportional to the partial pressure of CH4while independent of the partial pressure of CO2and CH4activation was the only kinetically controlledelementary step, the CRM reaction ratesover 4.5Ni0.5Co/SBA-15-CDunder the pressure of 2000 kPa could be expressed as

This rate equationis first-order to CH4 and zeroth-order to CO2, which is in good consistency with the results reported by Iglesiaetal, and the partial pressures of H2 and CO have no effect on .38-39

3.3 Apparent activation energy over 4.5Ni0.5Co catalyst at high pressure

The apparent activation energy of CRM reaction was measured over 4.5Ni0.5Co/SBA-15-CD at high pressure (2000 kPa), and the results are illustratedin Fig. 6. The measured activation energy of 106.5 kJ/mol was close to the reported values for 7%Ni/MgO(105kJ/mol)39 and Ni/SiO2(96.3 kJ/mol), 44 suggesting that the rate-determining step occurred mainly on Ni surface in 4.5Ni0.5Co/SBA-15-CD. Therefore, we speculated that the Co in 4.5Ni0.5Co/SBA-15-CD catalystfacilitated the adsorption of CO2andwas mainly covered with the adsorbedCO2* or O* species,while the trace Co in the catalystenhanced the catalyst stability by preventing sintering.45

Fig. 6 Arrhenius plots under high pressures in CRM over 4.5Ni0.5Co/SBA-15-CD. The apparent activation energy is shown in the insets.

3.3 Comparison between the kinetic studies over 4.5Ni0.5Co/SBA-15-CD catalyst underhigh pressure CRM with literatures

Some examples of the kinetic equations of CRM in previous studies from literatures are summarized in Table 2. Apparently, the kinetic equations obtained under atmospheric CRM might vary with the catalytic reaction systems.In the case that the reaction follows a Langmuir-Hinshelwood kinetic model, the equation used to express reaction rate might be relatively complicated (No. 1 in Table 2 is an example). In comparison, rCH4= k(PrCH4)x(PCO2)y(PH2O)z or rCH4= k(PrCH4)x(PCO2)y might be a more generalformfor the kinetic equations,46-47 with y and z valuesof zero or nearly zero being achieved over Ir/ZrO2, Ni/Kieselguhr, La2−xSrxNiO4perovskite-type oxides. Then the equation could be simplified as rCH4= k(PrCH4)x, which is quite similar to the one obtained in our study of 4.5Ni0.5Co/SBA-15-CD in pressurized CRM, suggesting that CH4 cracking was the sole kinetically controlled step in this study.

Table 2 Kinetic equations in previous studies under atmospheric CRM.

No

Equation

Description

Ref.

1

K1 is the methane adsorption equilibrium constant,

K2 is the methane decomposition (cracking) rate constant onthe metallic surface,

K3 is the adsorption equilibrium constant ofCO2 on the binary support to form the surface carbonate,

K4 isthe reaction rate constant between the carbon deposited on the surface ofmetallic clusters and the surface carbonatespecies.

Over Ni-X bimetallic catalysts, where X=Ca, K, Ba, La and Ce.

[31]

2

rCH4= kPCH4

Over Rh/Al2O3, Ni/MgO, Pt/ZrO2, Ir/ZrO2, Ru/Al2O3 catalysts

[38-43]

3

rCH4= k(PrCH4)α(PCO2)β(PH2O)γ

Over Ni/La/Al2O3 catalyst. Among the reaction orders for CH4, CO2, H2O, and H2, only the reaction order for CH4 was not zero, and the reaction orders could be affectedby the promoters.

[46]

4

rCH4= k (PCH4)m1(PCO2)n1

Over La2−xSrxNiO4 catalyst.

m1 = 0.41-0.89, n1 nearly zero.

[47]

5

rCH4= kPCH4

Over 4.5Ni0.5Co/SBA-15, under a total of 2.0 MPa

Present work

4. Conclusions

In this study, the catalytically stable 4.5Ni0.5Co/SBA-15-CD was used as a probe catalyst for kinetic study in pressurized CRM. The forward reaction rates were found to be proportional with the CH4 partial pressures (200 – 400 kPa) and unrelated to CO2 partial pressures(100 – 300 kPa) on 4.5Ni0.5Co/SBA-15-CD at 620-660 oC and 2000 kPa total pressure, confirming that the activation of methane was the kinetically relevant step. This study will provide some referencefor designing industrially practical catalysts for pressurized CRM.

Acknowledgements

We acknowledge financial support for this work from Natural Science Foundation of China (21073104) and the National Basic Research Program, Ministry of Science and Technology of China (973 Program, 2011CB201405). Huimin Liu acknowledges the financial support from Australia Research Council discovery early career researcher award (DE180100523). Hao Wu acknowledges the support of the Australian and Western Australian Governments and the North West Shelf Joint Venture Partners, as well as the Western Australian Energy Research Alliance (WA:ERA).

Reference

1. D. Chen, R. Lodeng, A. Anundskas, O. Olsvik and A. Holmen, Chem. Eng. Sci., 2001, 56, 1371-1379.

CrossRef    View Record in Scopus

2. B. Pawelec, S. Damyanova, K. Arishtirova, J. L. G. Fierro and L. Petrov, Appl. Catal. A, 2007, 323, 188-201.

CrossRef    View Record in Scopus

3. Z. Li, L. Mo, Y. Kathiraser and S. Kawi, ACS Catal., 2014, 4, 1526-1536.

CrossRef    View Record in Scopus

4. H. M. Liu, Y. M. Li, W. W. Yang, H. Wu and D. H. He, Chin. J. Catal., 2014, 35, 1520-1528.

CrossRef    View Record in Scopus

5. M. Ocsachoque, J. Bengoa and D. Gazzoli, Catal. Lett., 2011, 141, 1643-1650.

CrossRef    View Record in Scopus

6. C. E. Daza, C. R. Cabrera and S. Moreno. Appl. Catal. A, 2010, 378, 125-133.

CrossRef    View Record in Scopus

7. J. Q. Zhu, X. X. Peng and L. Yao, Int. J. Hydro. Energ., 2011, 36, 7094-7104.

CrossRef    View Record in Scopus

8. M. Ikeguchi, T. Mimura, Y. Sekine, E. Kikuchi and M. Matsukata, Appl. Catal. A, 2005, 290, 212-220.

CrossRef    View Record in Scopus

9. J. Huang, R. Ma, Z. Gao, C. Shen and W. Huang, Chin. J. Catal., 2012, 33, 637–644.

CrossRef    View Record in Scopus

10. H. Wu, H. M. Liu, W. W. Yang and D. H. He, Catal. Sci. Technol., 2016, 6, 5631-5646.

CrossRef    View Record in Scopus

11. Y. Li, Q. Ye, J. M. Wei and B. Q. Xu, Chin. J. Catal., 2004, 25, 326-330.

CrossRef    View Record in Scopus

12. H. M. Liu, Y. M. Li, H. Wu, J. X. Liu and D. H. He, Chin. J. Catal., 2015, 36, 283-289.

CrossRef    View Record in Scopus

13. M. C. J. Bradford and M. A. Vannice, Catal. Today, 1999, 50, 87-96.

CrossRef    View Record in Scopus

14. M. A. Goula, A. A. Lemonidou and A. M. Efstathiou, J. Catal., 1996, 161, 626-640.

CrossRef    View Record in Scopus

15. M. E. Dry, Catal. Today, 2002, 71, 227–241.

CrossRef    View Record in Scopus

16. H. Jahangiri, J. Bennett, P. Mahjoubi, K. Wilson and S. Gu, Catal. Sci. Technol., 2014, 4, 2210-2229.

CrossRef    View Record in Scopus

17. Y. F. Zhang, G. J. Zhang, B. M. Zhang, et al. Chem. Eng. J., 2011, 173, 592-597.

CrossRef    View Record in Scopus

18. J. B. Zhao, Y. D. Li, L. Tian, et al. Chin. J. Catal., 1998, 19, 491-493.

CrossRef    View Record in Scopus

19. J. N. Armor and D. J. Martenak, Appl. Catal. A, 2001, 206, 231-236.

CrossRef    View Record in Scopus

20. H. Zhou, T. Zhang, Z. Sui, Y. Zhu, C. Han, K. Zhu and X. Zhou, Appl. Catal. B: Environ, 2018, 233, 143-159.

CrossRef    View Record in Scopus

21. W. Yin and S. S. C. Chuang, Catal. Commun., 2017, 102, 62-66.

CrossRef    View Record in Scopus

22. B. AlSabban, L. Falivene, S. M. Kozlov, A. Aguilar-Tapia, S. Ould-Chikh, J. L. Hazemann, L. Cavallo, J. M. Basset and K. Takanabe, Appl. Catal. B: Environ, 2017, 213, 177-189.

CrossRef    View Record in Scopus

23. Z. H. Bao, Y. W. Lu and F. Yu, AICHE Journal, 2017, 63, 2019-2029.

CrossRef    View Record in Scopus

24. K. Nagaoka, K. Takanabe and K. Aika, Chem. Commun., 2002, 9, 1006-1007.

CrossRef    View Record in Scopus

25. K. Nagaoka, K. Takanabe and K. Aika, Appl. Catal. A, 2003, 255, 13-21.

CrossRef    View Record in Scopus

26. K. Tomishige, Y. Himeno, Y. Matsuo, Y. Yoshinaga and K. Fujimoto, Ind. Eng. Chem. Res.,2000, 39, 1891-1897.

CrossRef    View Record in Scopus

27. K. Tomishige, Y. Himeno, O. Yamazaki, Y. Chen, T. Wakatsuki and K. Fujimoto, Kinet. Catal., 1999, 40, 388-394.

CrossRef    View Record in Scopus

28. H. Wu, J. X. Liu, H. M. Liu and D. H. He, Fuel, 2019, 235, 868–877

CrossRef    View Record in Scopus

29. M. F. Mark, F. Mark and W. F. Maier, Chem. Eng. Technol., 1997, 20, 361-370

CrossRef    View Record in Scopus

30. T. H. Nguyen, L. Agata and K. Andrzej, Appl. Catal. B, 2015, 165, 389-398.

CrossRef    View Record in Scopus

31. M. S. Fan, A. Z. Abdullah and S. Bhatia, ChemSusChem, 2011, 4, 1643-1653.

CrossRef    View Record in Scopus

32. J. F. Munera, S. Irusta and L. M. Cornaglia, J. Catal., 2007, 245, 25-34.

CrossRef    View Record in Scopus

33. B. V. Ayodele, S. B. Abdullah and C. K. Cheng, Int. J. Hydro. Energ., 2017, 42, 28408-28424.

CrossRef    View Record in Scopus

34. U. Olsbye, T. Wurzel and L. Mleczko, Ind. Eng. Chem. Res., 1997, 36, 5180-5188.

CrossRef    View Record in Scopus

35. T. Osaki, T. Horiuchi and K. Suzuki, J. Chem. Soc. Fara.T., 1996, 92, 1627-1631.

CrossRef    View Record in Scopus

36. B. V. Ayodele, M. R. Khan, S. S. Lam and C. K. Cheng, Int. J. Hydro. Energ., 2016, 41, 4603-4615.

CrossRef    View Record in Scopus

37. H. M. Liu, Y. M. Li, H. Wu, H. Takayama, T. Miyake and D. H. He, Catal. Commun., 2012, 28, 168-173.

CrossRef    View Record in Scopus

38. J. M. Wei and E. Iglesia, J. Catal., 2004, 225, 116-127.

CrossRef    View Record in Scopus

39. J. M. Wei and E. Iglesia, J. Catal., 2004, 224, 370-383.

CrossRef    View Record in Scopus

40. J. M. Wei and E. Iglesia, Angew Chem. Int. Edit., 2004, 43, 3685-3688.

CrossRef    View Record in Scopus

41. J. M. Wei and E. Iglesia, J. Phys. Chem. B, 2004, 108, 4094-4103.

CrossRef    View Record in Scopus

42. J. M. Wei and E. Iglesia, J. Phys. Chem. B, 2004, 108, 7253-7262.

CrossRef    View Record in Scopus

43. J. M. Wei and E. Iglesia, Phys. Chem. Chem. Phys., 2004, 6, 3754-3759.

CrossRef    View Record in Scopus

44. M. C. J. Bradford and M. A. Vannice, Appl. Catal. A, 1996, 142, 97-122.

CrossRef    View Record in Scopus

45. E. Nikolla, J. Schwank and S. Linic, J. Catal., 2007, 250, 85-93

CrossRef    View Record in Scopus

46. M. H. Park, B. K. Choi and Y. H. Park, J. Nanosci. Nanotechno., 2015, 15, 5255-5258.

CrossRef    View Record in Scopus

47. C. Pichas, P. Pomonis and D. Petrakis, Appl. Catal. A, 2010, 386, 116-123.

CrossRef    View Record in Scopus