Using a specially developed, quasi in situ vacuum-sample-transfer system, the stepwise sequential sulfidation of CoMo/γ-Al2O3 was studied with transmission electron microscopy without exposing the catalyst to air. In a first step, the sulfidation was performed at 400 °C at either 1 or 10 bar pressure. In a second step, the sulfidation was performed at 600 °C and 1 bar. As the second sulfidation step was performed on the sample on the transmission electron microscopy grid, the same areas of the samples that had been studied for the first sulfidation step could be studied once more, providing detailed data on the changes in the sulfided phase. The slab length and degree of stacking have been studied in detail from the TEM/HREM images. Sulfidation at higher pressure or higher temperature results in a higher average slab size. Detailed study of the same areas of the catalysts before and after the second, more severe, sulfidation step shows that although the dispersion of the sulfided phase decreases, the total amount visible in the TEM images remains unchanged. This indicates that practically all the sulfide present is actually imaged on the micrographs. Additionally, detailed HRTEM study shows increased crystallinity of the slabs after the second sulfidation step. XPS analysis shows that after sulfidation at 400 °C and 1 bar, the degree of sulfidation is 95%, whereas after sulfidation at 600 °C and 1 bar, sulfidation is complete. The catalytic performance for thiophene hydrodesulfurization is much higher after sulfidation at 10 bar and 400 °C as compared to 1 bar and 400 °C, and decreases after the second sulfidation step (1 bar 600 °C). The latter effect is more pronounced for the sample sulfided at 10 bar in the first step, indicating that a distorted yet fully sulfided structure is the most active phase for thiophene HDS.

No abstract

. (1991). Influence of phosphate on the structure of sulfided alumina supported cobalt-molybdenum catalysts. Applied Catalysis, 68(1), 161-177. DOI: 10.1016/S0166-9834(00)84100-7 General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. AbstractThe influence of phosphate on the sulfiding rate of alumina-supported cobalt, molybdenum and cobalt-molybdenum catalysts has been studied by means of Temperature Programmed Sulfiding (TPS). Combination of the TPS results with recently published Temperature Programmed Reduction (TPR), Mossbauer spectrometry and nitrogen oxide adsorption measurements results in a detailed picture of the sulfidic catalyst. The sulfiding of cobalt ions in phosphorus-containing alumina-supported cobalt catalysts shifted to somewhat higher temperatures with increasing phosphorus content, most likely due to the presence of "Co-AlPO," phases. In the temperature region from 1000-1270 K, part of the cobalt sulfide species reacted with AlPO, to cobalt phosphides. The amount of cobalt which reduced to phosphides increased strongly with increasing phosphorus content and became about 70% of the total amount of cobalt present. The sulfiding pattern of phosphorus-containing Co-Ma/Al catalysts is only slightly influenced by increasing phosphorus content below 1000 K. All components including the CO-MO-O-P phase, present in the oxidic precursor, are relatively easy to sulfide. After sulfiding at 673 K, the Co-MO-S phase is most likely still to be associated with the AlPO, species. Analogous to cobalt catalysts, the major part of the cobalt in CO-MO-P/AI catalysts ultimately reacted to cobalt phosphides above about 1000 K. The sulfiding rate of the molybdenum ions is not changed by the presence of phosphates. MO& does not react with the phosphates to molybdenum phosphide probably because this reaction is thermodynamically restricted. Based on the surface structures, deduced from a combination of TPR and TPS data, the striking difference between the effect of phosphates on the hydrodenitrogenation (HDN) and on the hydrodesulphurisation (HDS) reactions is discussed.