Choudhary, V. R.; Mondal, K. C.; Mamman, A. S.; Joshi, U. A. Catal. Lett. 2005, 100 .... Choudhary, V. R.; Uphade, B. S.; Belhekar, A. A. J. Catal. 19...
0 downloads 0 Views 73KB Size


© Copyright 2006 American Chemical Society

Articles Oxy-CO2 Reforming of Methane to Syngas over CoOx/CeO2/SA-5205 Catalyst V. R. Choudhary,*,† K. C. Mondal,† and T. V. Choudhary‡ Chemical Engineering and Process DeVelopment DiVision, National Chemical Laboratory, Pune-411008, India, and 5518 Colony Court, BartlesVille, Oklahoma 74006 ReceiVed March 31, 2006. ReVised Manuscript ReceiVed June 15, 2006

The oxy-CO2 methane reforming (OCRM) process has been investigated over the CoOx/CeO2/SA-5205 catalyst at varying reaction temperatures (750-900 °C), O2/CH4 ratios (0.3-0.45), and space velocities (20 000100 000 cm3/g/h). With an increasing OCRM reaction temperature, the contribution from the CO2 methane reforming reaction increased while that from methane combustion reactions decreased. Correspondingly, there was an increase in the H2/CO ratio and a sharp decrease in reaction exothermicity. At 900 °C (gas hourly space velocity ) 46 000 cm3/g/h and O2/CH4 ) 0.4), the OCRM reaction over the CoOx/CeO2/SA-5205 catalyst was mildly endothermic with >90% CH4 conversion, >95% H2 selectivity, and a H2/CO ratio of 1.63. CH4 conversion was relatively unaffected by the O2/CH4 ratio used in the OCRM reaction; however, CO2 conversion decreased on increasing the O2/CH4 ratio. While H2 selectivity was not significantly affected by the O2/CH4 ratio, the H2/CO ratio increased linearly with an increasing O2/CH4 ratio. The endothermicity of the reaction was found to decrease with an increasing CH4/O2 ratio, which can be explained on the basis of increased contribution from the methane partial oxidation reaction with an increasing O2/CH4 ratio.

1. Introduction The CO2 reforming of methane to syngas (the feedstock for Fischer-Tropsch and methanol production processes) is a reaction of significant commercial importance.1-9 Moreover, two * To whom correspondence should be addressed. Tel.: 011912056265508. Fax: 91-202-589-3041. E-mail: [email protected]. † National Chemical Laboratory. ‡ Bartlesville, Oklahoma. (1) Bradford, M. C. J.; Vannice, M. A. Catal. ReV.sSci. Eng. 1999, 41, 1. (2) Hu, Y. H.; Ruckenstein, E. AdV. Catal. 2004, 48, 297. (3) Takanabe, K.; Nagaoka, K.; Nariai, K.; Aika, K. J. Catal. 2005, 232, 268. (4) Ross, J. R. H. Catal. Today 2005, 100, 151. (5) Choudhary, V. R.; Mondal, K. C.; Mamman, A. S.; Joshi, U. A. Catal. Lett. 2005, 100, 271. (6) Takanabe, K.; Nagaoka, K.; Nariai, K.; Aika, K. J. Catal. 2005, 230, 75. (7) Li, D.; Hacarlioglu, P.; Oyama, S. T. Top. Catal. 2004, 29, 45. (8) Ruckenstein, E.; Wang, H. Y. Appl. Catal., A 2000, 204, 257-263. (9) Wang, H. Y.; Ruckenstein, E. Appl. Catal., A 2001, 209, 207-215.

greenhouse gases (CO2 and CH4) are consumed in the above process. However, rapid carbon deposition on the catalyst is a very serious problem in the CO2 methane reforming process (CMR); generally, the carbon deposition rate is very high for the Ni- and Co-based catalysts and relatively lower for the noblemetal-based catalysts. Because noble metals are expensive and have limited availability, it is interesting to consider non-noblemetal catalysts.2 A recent study, which involved several Cobased catalysts supported on highly macroporous and sintered silica-alumina, showed that supported CoOx/CeO2 showed promising performance for the CMR reaction;10 the rate of carbon deposition for these catalysts was extremely low (90%). The corresponding unsupported CoOx/CeO2 catalyst, however, showed a considerably higher carbon deposition rate (0.35 mgC gCat-1 h-1). Unfortunately, because of its highly endothermic nature, CMR is a highly energy intensive process. To increase the (10) Choudhary, V. R.; Mondal, K. C.; Joshi, U. A. Submitted.

10.1021/ef060138o CCC: $33.50 © 2006 American Chemical Society Published on Web 07/13/2006

1754 Energy & Fuels, Vol. 20, No. 5, 2006

Choudhary et al.

energy efficiency of the syngas production process, it is interesting to consider the combined oxy-CO2 reforming (OCRM) process.11,12 Moreover, the oxy-CO2 process can provide increased flexibility for tuning the H2/CO ratio to the requirements of the subsequent syngas-to-liquid hydrocarbon processes. The oxy-CO2 reforming process has been previously investigated over NiO-MgO- and CoO-MgO-based catalyst systems.13-17 In this study, we have investigated the OCRM process over the CoOx/CeO2/SA-5205 catalyst as a function of the reaction temperature (750-900 °C), O2/CH4 ratio (0.30.45), and space velocity (20 000-100 000 cm3/g/h). Our studies show that CoOx/CeO2/SA-5205 is a promising candidate for the oxy-CO2 reforming of methane processes. 2. Experimental Section The low surface area (