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Surface‐Dependent Activation of Model α‐Al 2 O 3 ‐Supported P‐Doped Hydrotreating Catalysts Prepared by Spin Coating
Author(s) -
Garcia de Castro Ricardo,
Bertrand Jérémy,
Rigaud Baptiste,
Devers Elodie,
Digne Mathieu,
LamicHumblot AnneFélicie,
Pirngruber Gerhard,
Carrier Xavier
Publication year - 2020
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202001882
Subject(s) - hydrodesulfurization , catalysis , sulfidation , x ray photoelectron spectroscopy , sulfide , dispersion (optics) , phosphate , heteroatom , chemical engineering , coating , materials science , chemistry , inorganic chemistry , organic chemistry , ring (chemistry) , physics , optics , engineering
Requirements for improved catalytic formulations is continuously driving research in hydrotreating (HDT) catalysis for biomass upgrading and heteroatom removal for cleaner fuels. The present work proposes a surface‐science approach for the understanding of the genesis of the active (sulfide) phase in model P‐doped MoS 2 hydrotreating catalysts supported on α‐Al 2 O 3 single crystals. This approach allows one to obtain a surface‐dependent insight by varying the crystal orientations of the support. Model phosphorus‐doped catalysts are prepared via spin‐coating of Mo–P precursor solutions onto four α‐Al 2 O 3 crystal orientations, C(0001), A(11 2 ‾ 0), M(10 1 ‾ 0) and R(1 1 ‾ 02) that exhibit different speciations of surface ‐OH. 31 P and 95 Mo liquid‐state NMR are used to give a comprehensive description of the Mo and P speciation of the phospho‐molybdic precursor solution. The speciation of the deposition solution is then correlated with the genesis of the active MoS 2 phase. XPS quantification of the surface P/Mo ratio reveal a surface‐dependent phosphate aggregation driven by the amount of free phosphates in solution. Phosphates aggregation decreases in the following order C(0001)≫M(10 1 ‾ 0)>A(11 2 ‾ 0), R(1 1 ‾ 02). This evolution can be rationalized by an increasing strength of phosphate/surface interactions on the different α‐Al 2 O 3 surface orientations from the C(0001) to the R(1 1 ‾ 02) plane. Retardation of the sulfidation with temperature is observed for model catalysts with the highest phosphate dispersion on the surface (A(11 2 ‾ 0), R(1 1 ‾ 02)), suggesting that phosphorus strongly intervene in the genesis of the active phase through a close intimacy between phosphates and molybdates. The surface P/Mo ratio appears as a key descriptor to quantify this retarding effect. It is proposed that retardation of sulfidation is driven by two effects: i) a chemical inhibition through formation of hardly reducible mixed molybdo‐phosphate structures and ii) a physical inhibition with phosphate clusters inhibiting the growth of MoS 2 . The surface‐dependent phosphorus doping on model α‐Al 2 O 3 supports can be used as a guide for the rational design of more efficient HDT catalysts on industrial γ‐Al 2 O 3 carrier.