Hydrogen production from gasoline using nickel -based catalysts.

Abstract

Catalysts comprising nickel supported on a reducible ceria-zirconia mixed oxide were prepared with a range of nickel loadings. Supports were synthesized by coprecipitation, calcined in air, and impregnated with nickel. The effects of nickel loading on catalytic performance for the autothermal reforming of isooctane were investigated. It was found that there is an interaction between nickel and the reducible oxide support. The effects of this interaction are most strongly evident at low nickel loading, and include modification of the reduction temperatures of both the nickel and support components, and significant increase in resistance to carbon deposition under autothermal reforming reaction conditions. At higher nickel loadings the carbon resistance is lost, and reaction at low H₂O/C and O/C ratios leads to heavy coke deposition. The exact nature of the nickel-support interaction in these catalysts is not clear from the current investigation. It is possible that the effects are due to limited incorporation of nickel into the support lattice, thereby introducing oxygen defects and new types of catalytic sites, or it may simply be an effect of interfacial contact between small nickel domains and the support, resulting in an enhanced rate of oxygen delivery to nickel during reaction. The lowest nickel loading studied, 1 wt%, yielded catalysts that had stable operation under demanding autothermal reforming conditions. At a H₂O/C and O/C of 0.5, high activity was maintained over the course of eight hours on stream. Given the propensity of nickel catalysts to form carbon during reforming of hydrocarbons, this result is novel and unexpected. It offers the opportunity to develop fuel processing technology around catalysts which do not use precious metals, and can operate with feed stoichiometries previously thought unusable. In an effort to develop an integrated fuel processor based on these catalysts, they were tested as washcoats in prototype microchannel reactors. Catalyst performance in the microchannel reactors was generally poor as compared to the same catalysts tested in a packed bed configuration. This seems to be attributable to the differences in heat transfer between the two reactor materials and geometries, leading to different temperature profiles in the reactors. This indicates that reactor design in microchannel systems will need to be adjusted for reactions with high exotherms or endotherms.