Characterization of hydroprocessing catalysts by resolved temperature-programmed desorption, reduction and sulfiding

A flow system is described for carrying out temperature-programmed desorption and reaction experiments with resolution of the desorbed products by on-stream gas chromatographie analysis. The apparatus has been used to characterize hydroprocessing catalysts (MoO3, γ-Al2O3, MoO3γ-A12O3 having various MoO3 contents, CoMoγ-Al2O3, NiMoγA12O3, and NiWγ-Al2O3) by temperature-programmed desorption with He, temperature-programmed sulfiding with H2S in H2, and temperature-programmed reduction with H2. The results show that a decreasing temperature of appearance of H2S peaks in the TPR spectra of sulfided MoAl2O3 catalysts corresponds to anincreasing Mo content and increasing catalytic activity. TPR data provide a rapid qualitative test for the presence of incompletely sulfided MoO3 on the catalyst surfaces. Quantitative TPR data associated with the formation of sulfur anion vacancies on the surface indicate that only a small fraction of the sulfur is removed by reaction with H2, this fraction being higher for the promoted catalyst CoMoAl2O3 (~0.3 molecule/nm2) than for the less active, unpromoted catalyst MoAl2O3 (~0.06 molecule/nm2).