Pt/Nb‐WO_x for the chemoselective hydrogenolysis of glycerol to 1,3‐propanediol: Nb dopant pacifying the over‐reduction of WO_x supports

Selective hydrogenolysis of glycerol to 1,3‐propanediol（1,3‐PD） is an important yet challenging method for the transformation of biomass into value‐added chemicals due to steric hindrance and unfavorable thermodynamics. In previous studies, chemoselective performances were found de‐manding and sensitive to H2 pressure. In this regard, we manipulate the chemical/physical charac‐teristics of the catalyst supports via doping Nb into WOx and prepared 1D needle‐, 2D flake‐, and 3D sphere‐stack mesoporous structured Nb‐WOx with increased surface acid sites. Moreover, Nb dop‐ing can successfully inhibit the over‐reduction of active W species during glycerol hydrogenolysis and substantially broaden the optimal H2 pressure from 1 to 5 MPa. When Nb doping is 2%, sup‐ported Pt catalysts showed promising performance for the selective hydrogenolysis of glycerol to 1,3‐PD over an unprecedentedly wide H2 pressure range, which will guarantee better catalyst sta‐bility in the long run, as well as expand their applications to other hydrogen‐related reactions.

Effect of promoters on the selective hydrogenolysis of glycerol over Pt/W-containing catalysts

Diverse promoters,including noble metals（such as Ru,Ir and Rh） and transition metal oxides（such as Re,La,Fe,Zr,Sn and Ce oxides） were introduced into Pt/WOx and Pt/WOx/Al2O3 catalysts to investigate the ability of these promoters to modify activity and selectivity during glycerol hydrogenolysis to 1,3-propanediol.Among these,La exhibited the greatest promotional effect;the introduction of 0.1% La to the Pt/WOx improved activity,selectivity and stability,although the significant increase in selectivity came at the cost of a slight activity loss in the case of the Pt/WOx/Al2O3 catalyst.Transmission electron microscopy,high angle annular dark field scanning tunneling electron microscopy and NH3-temperature programmed desorption all demonstrated that the introduction of La generates a greater quantity of acidic sites on the catalyst surface,and that the majority of the La species are associated with Pt particles.Most of the other additives resulted in only minimal improvements or even detrimental effects with regard to both activity and selectivity,although some appear to improve the stability of the catalyst.

Understanding the deactivation behavior of Pt/WO3/Al2O3 catalyst in the glycerol hydrogenolysis reaction

The selective hydrogenolysis of glycerol to 1,3-propanediol is a highly important reaction for both improving the profitability of biodiesel and valorization of biomass.While intensive research efforts have been devoted to enhancing the catalytic activity and selectivity,little is focused on the stability although the latter is of paramount importance to practical applications.In this work,we investigated the stability of Pt/WO3/Al2O3 and observed a continuous deactivation trend during a 700 h time-on-stream run.Neither the leaching of active W nor the coking was responsible for the deactivation.Instead,XRD,HAADF-STEM and CO chemisorption results clearly showed the occurrence of significant aggregation of Pt particles,which caused a remarkable decrease of Pt-WOx interfacial sites.As a consequence,strong Br?nsted acid sites which were in situ formed by H2 dissociation at the Pt-WOx interfacial sites were reduced,leading to the deactivation of the catalyst.

Understanding the promotional effect of Au on Pt/WO_3 in hydrogenolysis of glycerol to 1,3-propanediol

Pt/Au/WO_3 bimetallic catalysts were prepared by impregnation of Pt onto preformed Au/WO_3,obtained by a hexadecyl trmethyl ammonium bromide（CTAB）-assisted one-pot synthesis method.The resulting Pt/Au/WO_3 catalysts exhibited remarkable synergistic effects for selective hydrogenolysis of glycerol to 1,3-propanediol. The characterization results showed that doping of Au promoted the reduction of both Pt and W at low temperatures and uniform dispersion of Pt on the WO_3 support. Furthermore, more low-valence Pt species were produced on the WO_3 surface after introduction of Au. These changes in electronic properties resulted in enhancement of both glycerol conversion and selectivity for 1,3-propanediol.

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