Subnanometer Dispersed Pd Catalyst For Succinic Acid Selective Hydrogenation

Biomass-derived molecules are a promising class of alternative resources with advantages of being widely available, renewable and potentially carbon-neutral. Succinic acid (SUC) as one of the most interesting biomass-derived platform chemicals can be generated via bioprocessing. The hydrogenation of SUC to produce valuable C4 compounds, including y-butyrolactone (GBL),1,4-butanediol (BDO) and tetrahydrofuran (THF) has attracted significant interest for the broad market of the downstream industries. In particular, GBL is an important intermediate for the production of C4 chemicals, polymers, solvents, pesticides and so forth. Therefore, it is valuable to develop green and efficient processes for converting biomass-derived SUC into GBL. The reported catalytic processes were either performed in the presence of organic solvents (1,4-dioxane or ethanol) or involved high Pd loadings (2%-5%), resulting in high operating cost and conflict with stringent environmental concerns. Such disadvantages make it necessary and urgent to design and cultivate heterogeneous catalysts with low Pd loading, in combination with green solvents for the liquid-phase hydrogenation of SUC.Subnanometer dispersed Pd species supported on ?-AlOOH nanosheets (Pd/?-A100H) were prepared for their high atom-efficiency offering practical value for selective hydrogenation of SUC to GBL. The conversion of SUC can reach over 95% over 0.2Pd/y-AlOOH using 1,4-dioxane as solvent. The supported Pd single atom catalyst (Pd1/?-AlOOH) exhibits 30- and 1100-fold increase in the catalytic activity compared with the supported clusters Pd13/?-AlOOH and Pdss/y-AlOOH for the selective hydrogenation of succinic acid to y-butyrolactone, respectively. In addition, Pd single atoms in the catalyst 0.2Pd/y-AlOOH accounts for 86.6% of the overall catalytic activity and can serve as the most efficient catalytic active sites.Addition, subnanometer Pd particles supported on zirconia was systhesized by a micro wave-assisted hydrothermal method. The presence of subnanometer Pd particles on the zirconia surface was confirmed by two dimensional Gaussian-function fits of aberration-corrected high-angle annual dark-field images. These subnanometer Pd catalysts exhibit high catalytic performance for the hydrogenation of biomass-derived succinic acid to y-butyrolactone in water. The 0.2Pd/ZrO2 catalyst with ultra-low Pd loading of 0.2 wt% demonstrates high selectivity (95%) to y-butyrolactone using water as solvent at 473 K and 10 MPa. Moreover, it can be reused at least 6 times without loss of catalytic activity, illustrating high performance of the subnanometer Pd catalyst.Structures and energies of PdN clusters supported ony-AlOOH and ZrO2 with N= 1,4,8 and 13 were determined through density functional theory (DFT) to evaluate the cluster size effect and the support effect. Low-energy PdN isomers, taken from a large pool of candidate structures for all cluster sizes, are used in systematic researches for the most stable molecularly adsorbed hydrogen and dissociatively adsorbed hydrogen. Molecular adsorption of hydrogen occurs preferentially on the atop sites of the supported PdN clusters while dissociative adsorption favors the face sites. Dissociative adsorption is energetically preferred to molecular adsorption for all the cluster sizes, especially on supported single Pd atom. Both molecular and dissociative adsorption energies decrease with the increasing clusters size due to the declining electron mount transferred between supports and PdN clusters. The molecular adsorption energies on supported PdN clusters with range of 0.84 eV to 2.63 eV and the dissociative adsorption energies with the range of 0.57 eV to 3.80 eV are both larger than those on bare PdN clusters, indicating the promoting effect of the supports.