Abstract:
The aim of this study is to design Co-based CDRM (catalytic dry reforming of methane) catalysts and to understand the CDRM reaction kinetics over their surface. The thesis consists of two parts. In the first part, a 5 wt% Co-2 wt% Ce/δ-Al2O3 catalyst was designed and tested for its CDRM performance. Temperature, CH4/CO2 feed ratio and space velocity were used as experimental parameters. In the second part, 10 wt% Co-2 wt% Ce/ZrO2 catalyst was prepared and kinetic tests were conducted over the catalyst in order to obtain a power law type and plausible mechanistic rate expressions for CDRM. For both catalysts, Ce was used as a promoter in order to increase the oxygen storage capacity via controlling the electronic structure of the metals over the support. For Co-Ce/δ-Al2O3 the results have shown that the catalyst suffers from severe coke deposition and consequent activity loss. In the tests, increasing temperature increased the activity although at low temperatures catalyst deactivated relatively slower. CDRM did not occur on the catalyst for high space velocities (for W/F value of mL/h g-cat.) though for the space velocities of 10000 mL/h g-cat. and 20000 mL/h g-cat., almost the same initial performances were observed. The kinetic study over Co-Ce/ZrO2 catalyst revealed that the reaction could be expressed by a simple power-law rate equation, with reaction order of 1.0751 for CH4 and -0.0988 for CO2, indicating that the reaction rate is proportional to the partial pressure of methane while there is a very small inhibition effect of carbon dioxide. This inhibition effect may be due to CO2 and CH4 competing for the same active sites. An ER mechanism having the reaction of adsorbed CO2 with gas phase CH4 leading directly to products, and an LH mechanism having surface reaction of the adsorbed reactants to form products H2 and CO as the rate determining steps are found plausible. On the other hand, the results clearly indicate that further FTIR-DRIFT analysis is necessary for finding the mechanism of CDRM reaction on Co-Ce/ZrO2 system. In the mixed feed tests to determine effect of product, the correlation coefficient (R2) was found so small that any observation could not be possible.
