Experimental and DFT study of (sorption-enhanced) steam methane reforming over bimetallic Ni-Cu catalysts

The catalytic performance of a monometallic Ni/Al2O3 and three bimetallic Ni-Cu catalysts (with Cu loading of 2.5, 5, and 7.5 mol%, respectively) for the (sorption-enhanced) steam methane reforming reaction was evaluated. Physico-chemical characterization of the materials confirmed the formation of Ni-Cu alloy and the even distribution of active metals within the porous high-surface area support. All three bimetallic catalysts showed enhanced methane conversion compared to the conventional Ni/Al2O3 catalyst at higher temperatures (800 °C), which was attributed to the promotion of the water–gas shift reaction by the addition of Cu. The experimental observations were supported by the Density Functional Theory calculations of carbon and oxygen adsorption on the mono and bimetallic surfaces. Ni3Cu1 and Ni1Cu1 were calculated to have a similar level of catalytic activity as Ni, based on results from a microkinetic model of the steam methane reforming reaction. Ni1Cu3 showed slightly lower activity, potentially due to its low carbon adsorption ability which impedes the rate-determining methane decomposition process. The SMR reaction was further improved by adding calcium oxide as the CO2 sorbent, which increased both methane conversion and hydrogen yield. Ni3Cu1/Al2O3 and Ni1Cu1/Al2O3 were identified as promising SMR catalysts with a high methane conversion of approximately 90 % at 800 °C and 97 % at 700 °C, without and with the sorbent, respectively.