WGS activity and kinetics of ZrO2 supported tri-metallic catalysts

Abstract

The current study is the part of an ongoing project aiming to design and develop high performance, steam tolerant, non-pyrophoric WGS catalyst(s) to be used in a demo-scale fuel processor producing PEM grade hydrogen for PEM fuel cells. The current work involves (i) testing and optimizing WGS performance of ZrO2 supported Pt-based trimetallic formulations, (ii) deriving a simple power law type WGS kinetic expression for the high performance sample. The performance tests were conducted under the flow of ideal and realistic feeds, and in the tests H2O/CO ratio for each type of feed and temperature were used as the experimental parameters. In this context, a series of Pt-Re-V/ZrO2 catalysts, whose Pt content was fixed at 1wt.% but Re and V loadings varied as 0.5 or 1 wt.%, were prepared by incipient-to-wetness impregnation method. All the catalysts were characterized by SEM, Xray diffraction, XPS and Raman spectroscopy. The WGS performance of the freshly reduced catalysts were determined at 300, 350 and 400 ºC in terms of their CO conversion activity and net H2 production ability. XPS and Raman spectroscopy revealed that VO2 and polyvanadate surface species were present in the catalysts but no bulk V2O5 crystals, indicating that vanadium was well-dispersed on the surface. All the catalyst performances were found reasonable in terms of providing high CO conversion and stability under ideal feed conditions. The highest CO conversion rate for realistic feed was achieved over 1Pt1Re-0.5V/ZrO2 catalyst at 300 °C for H2O/CO ratio of 16.2. The kinetic tests were performed over 1Pt-1Re-0.5V/ZrO2 catalyst at 300 °C under atmospheric pressure. Initial reaction rates were obtained by varying residence time and the partial pressure of CO, H2O, H2, CO2 and CH4 in the feed stream. A power-law type rate expression, whose kinetic constants calculated through applying non-linear regression analysis on MATLABTM environment, was proposed. The reaction orders with respect to CO, H2O, H2 and CO2 were estimated as 0.96, -0.62, -0.30 and -0.77, respectively, and apparent activation energy was predicted as 58.09 kj/mol between 300-350 °C.