Non-precious metal (pre-)commercial catalysts for Pd membrane water gas shift

Abstract

Development of membrane-reactors for use in pre-combustion CO2 capture power schemes is of great interest. The local environment of the catalysts at the catalytic membrane reactor (CMR) conditions is different from conventional applications, inducing changes in demands to the catalyst properties. Here, the use of low-cost base metal catalysts in membrane assisted-water gas shift (MWGS) reaction is studied. A conventional high temperature FeCr-based shift catalyst was studied in a membrane reactor with feed gas mimicking combined-cycle power plant process gas. Combining the catalyst with hydrogen selective Pd membranes, results in approximately 95% hydrogen recovery and CO conversion. No loss of selectivity (through methanation and Fisher–Tropsch reaction) and stability was found during tests, according to expectations, i.e steam/H2 > 0.5 and steam/CO > 2. However, in order to meet these conditions in an ATR + pre-shift based natural gas combined cycle (NGCC) process, steam injection is required at the cost of an efficiency penalty and higher membrane surface area. Using severe conditions representing coal-gasification (IGCC) conditions with high CO concentration and steam/CO < 2, higher hydrocarbons and oxygenates are indeed being formed and catalyst deactivation is unavoidable. For both coal and gas-fired combined-cycle power plants, an alternative catalyst (Topsøe ZnO/ZnAl2O4 type catalyst) was identified with similar hydrogen recovery and activity but superior selectivity and stability to the FeCr type catalyst at steam/H2 < 0.5 and steam/CO < 1.