The mechanism of pyridine hydrogenolysis on molybdenum-containing catalysts II. Hydrogenation of pyridine to piperidine

The kinetics of pyridine hydrogenation was studied at high hydrogen pressures on a Mo-Al oxide and a Co-Mo-Al oxide catalyst. The rate equation was found to be r = kPpyrPH2nPpyro, in which n is 1.5 at 300 and 375 °C and 1.0 at 250 °C. This rate equation can be derived assuming strong adsorption of pyridine and its products with identical adsorption constants. The (hydro)cracking of piperidine appears to have a low order in hydrogen, probably lower than 0.5. The adsorption behavior of nitrogen bases and hydrogen on alumina and the molybdenum-containing catalysts was investigated by the gas chromatographic method. The adsorption of the nitrogen bases appeared to be very strong on both catalysts, and varied in the order piperidine > pyridine > ammonia. Hydrogen also showed a strong adsorption. Hydrogen and nitrogen bases appeared to adsorb on different sites.