The dehydrogenation of ethanol to acetaldehyde has been studied over a series of unsupported copper-chromium catalysts. The results indicate that the sintering occurs in both reduction and dehydrogenation processes. The Cr2O3-promoted copper catalysts prevent sintering in both reduction and reaction processes. The catalyst with Cr/Cu molar ratio of 4/40 has the highest activity and stability. The temperature-programmed reduction results indicate that the good dispersion of Cr2O3 promoter helps to prevent sintering in the reduction process. The catalyst which contains Cu and CuCr2O4 has a lower initial activity and the thermal stability is as poor as the unpromoted one. Cu0 instead of Cu2+ is the active site. The TOFs of promoted catalysts with Cr/Cu= 1/40 to 6/40 are lower than that of unpromoted catalyst, and thus die chromic oxide is not just a textural promoter of Cu. The higher copper surface areas of promoted catalysts easily overcome the loss in TOFs.
