| Popis: |
A Cr-promoted Ni/SiO2 catalyst was prepared by adding Cr(N03)3 to a Ni(OH)2/SiO2 precursor. After hydrogen reduction at various temperatures, the solid was studied by magnetic methods, infrared spectroscopy and tested for ethane hydrogenolysis, benzene and carbon monoxide hydrogenations. Chromium addition results in an in- crease in the rate of nucleation and in the sintering of Ni particles. Ni-Cr and Ni-Cr-Si alloys are formed by reduction at high temperatures. The presence of chromium affects neither the electronic properties of nickel nor its activity in the ethane hydrogenolysis and benzene hydrogenation at low temperature. At high temperature, the reaction with benzene leads to toluene by a bifunctional process. In the CO hydrogenation, the Cr additive results in an increase of the activity and the selectivity for low temperature reduction because of the better reducibil-ity of nickel in the presence of chromium. Dehydrogenation and isomerization reactions occur on the chromium phase. When Ni-Cr a lloys are formed, the dilution effect suppresses the above enhancement. In the reaction of methanation, chromium has no beneficial effect on the sulfur resistance of nickel. |
