Using XRD extrapolation method to design Ce-Cu-O solid solution catalysts for methanol steam reforming to produce H2: The effect of CuO lattice capacity on the reaction performance

Abstract

Targeting to obtain efficient catalysts for methanol steam reforming to manufacture H2, Ce-Cu-O solid solutions having different Ce/Cu ratios were designed with XRD extrapolation method established by our lab. It is quantified that the lattice capacity of Ce-Cu-O solid solution is 0.109 g CuO/g CeO2, equaling to a Ce/Cu mole ratio of 81/19. Therefore, Cu2+ cations can maximally substitute 19% Ce4+ in cubic fluorite CeO2 matrix to form a stable solid solution in pure phase. Further increasing CuO content leads to the generation of surface CuO species. Below the lattice capacity, the quantity of surface defects/oxygen vacancies improves by increasing the lattice Cu2+ amount until it reaches the lattice capacity. The formation of pure phase solid solution is beneficial to generate surface active oxygen species (O2-) and alkaline sites, which is vital for the reaction. The sample with a lattice capacity amount of CuO (Ce0.8Cu0.2Ox) possesses the largest amount of these surface sites. In addition, this sample has appropriate amounts of both Cu+ and Cu0 after reducing, being favorable for the redox cycle during the reaction. Hence, it shows the optimal reaction performance in all the samples. A lattice capacity threshold effect is evidently observed for the reaction. It is proposed that the best catalysts for the reaction is able to be fabricated by doping CeO2 with the lattice capacity amount of CuO.