Requirements for improved catalytic formulations is continuously driving researchi nh ydrotreating (HDT)c atalysis for biomass upgrading and heteroatom removalf or cleanerf uels. The present work proposes as urface-science approach for the understanding of the genesis of the active (sulfide) phase in model P-doped MoS 2 hydrotreating catalysts supported on a-Al 2 O 3 single crystals. This approach allows one to obtain as urface-dependenti nsightb yv arying the crystal orientationso ft he support. Model phosphorusdoped catalysts are preparedv ia spin-coating of MoP precursor solutions onto four a-Al 2 O 3 crystalo rientations, C(0001), A(112 0), M(101 0) and R(11 02) that exhibit different speciations of surface-OH. 31 Pa nd 95 Mo liquid-state NMR are used to give ac omprehensive description of the Mo andP speciation of the phospho-molybdic precursor solution. The speciation of the deposition solution is then correlatedw ith the genesiso ft he active MoS 2 phase.X PS quantificationo f the surfaceP /Mo ratio reveal as urface-dependent phosphate aggregation driven by the amount of free phosphates in solution.P hosphates aggregation decreases in the following order C(0001) @ M(101 0) > A(112 0), R(11 02). This evolution can be rationalized by an increasing strength of phosphate/surface interactions on the different a-Al 2 O 3 surface orientations from the C(0001) to the R(11 02) plane. Retardation of the sulfidation with temperature is observed for model catalystsw ith the highest phosphate dispersion on the surface(A(112 0), R(11 02)), suggesting that phosphorus strongly intervene in the genesis of the activep hase through ac lose intimacy between phosphates and molybdates.T he surface P/Mo ratio appears as ak ey descriptor to quantify this retarding effect.I ti sp roposedt hat retardation of sulfidation is drivenb yt wo effects:i)achemicali nhibition through formation of hardly reducible mixed molybdo-phosphates tructures and ii)a physicali nhibition with phosphate clusters inhibiting the growth of MoS 2 .T he surface-dependent phosphorus dopingo nm odel a-Al 2 O 3 supportsc an be used as ag uide for the rational design of more efficient HDT catalysts on industrial g-Al 2 O 3 carrier.
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