Design of micro-shell Cu-Al porous ceramometals as catalysts for the water-gas shift reaction

Abstract

XRD, NMR, SEM with mapping, and XPS were used to examine the structure and microstructure of porous ceramometals, CuAlO/CuAl, synthesized by mechanochemical alloying of a mixture of Cu + Al (Cu:Al = 87:13 wt%) followed by hydrothermal treatment and heat treatment in air. The egg-shell nature of the microstructure was revealed: the metallic cores consisting of copper and aluminum alloys are surrounded by the oxide matrix containing copper oxides and X-ray amorphous mixed oxides of copper and aluminum. Catalytic activity of ceramometals in the water-gas shift reaction (WGSR) estimated for their fine fractions at 240 °C and expressed as efficient first-order rate constants is lower than that of a CuZnAl oxide catalyst due to the lower (approximately by an order of magnitude) specific surface area of the ceramometals. The specific activity of ceramometals expressed as the specific rate constant related to the unit surface area of metallic copper exceeds that for the CuZnAl oxide catalyst and correlates with the content of crystallized intermetallics. Mechanical, textural and thermophysical properties of ceramometals were assessed. The presence of ultramacropores with sizes up to tens of microns was shown to be typical for ceramometals. As a result, the activity of granulated ceramometal catalysts in the WGSR, due to a high diffusion permeability, is comparable with that of granulated CuZnAl oxide. A mild leaching substantially increases the activity of cermet granules.