Hydrogenation on copper chromite catalyst. Role of the cuprous ions in the methanol synthesis from syngas

Mixed copper chromium oxides have been extensively studied in our laboratory. From these studies, it was showed that the reduction under hydrogen alone of the precursor oxides leads to the formation of cuprous ions located in the octahedral sites of the spinel matrix Cr2O3-Y, and hydridic species stored in the solid. The use of these prereduced catalysts for the methanol synthesis from syngas indicates an excellent correlation between the methanol activity and the Cu+B concentration. In absence of prereduction, the direct use of H2/CO mixture, modifies the ionic distribution of the copper species and the beneficial effect of the spinel structure is lost as indicated by X-ray diffraction and X.P.S techniques. From these results it was assumed that, on the prereduced mixed copper chromium oxides, the Cu+-H-association plays an essential role in the methanol formation. By a close analogy with the unsaturated organic compounds hydrogenation, a mechanism with formyl and methoxy species intermediates, is proposed

Characterization by

L’acide 12-molybdovanadophosphorique contenant un seul atome de vanadium dans la structure de Keggin, ainsi que son sel acide de sodium (Na1,5H2,5) perdent leur eau de constitution vers 593 K, entraînant un départ d’atomes d’oxygène de l’unité de Keggin. Dans le cas de l’acide, la RMN 51v du solide montre la formation lors de cette déshydratation d’une quantité importante de vanadium (V) tétracoordiné extérieur aux unités de Keggin (signal RMN B). Dans le cas du sel acide de sodium, aucun signal de type B n’apparaît lors de la déshydratation. Par ailleurs, il a été montré que la présence du sodium dans l’hétéropolyacide fait très nettement chuter l’activité catalytique