Optimization Of Two-dimensional Materials As Supports For Palladium Catalysts And Their Application In Hydrogenation Catalysis

In recent years,two-dimensional materials have shown excellent properties in the fields of adsorption and catalysis.Due to its good stability and tunable acidity and alkalinity,it is an excellent carrier for the construction of supported noble metal catalysts.Doping of non-metallic elements is one of the important means to further modulate the properties of two-dimensional materials.In this paper,g-C₃N₄ and h-BN were modified by doping with phosphorus element to construct supported Pd catalysts.The catalytic hydrogenation performance of the catalysts were investigated.The hydrogenation of styrene is a typical structure-sensitive reaction,and the activity of the catalyst is closely related to the particle size and valence of Pd.In this paper,phosphorus-containing organic compounds such as hydroxyethylidene diphosphoric acid（HEDP）were used as phosphorus precursors to copolymerize with dicyandiamide,to prepare phosphorus-doped g-C₃N₄（CNP）,which was further loaded with Pd and applied to styrene hydrogenation.The results show that the activity of the CNP-supported Pd catalyst is greatly improved compared with that of g-C₃N₄.Taking the reaction frequency（TOF）value of atomic Pd as the evaluation index of catalyst activity,the catalyst with the optimal P doping amount and the most suitable Pd loading amount of 0.2 wt%Pd/CNP-0.1has a TOF value of 18974 h^-1.Comparatively,the TOF value of Pd/g-C₃N₄is only 7002 h^-1.The characterization results of X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,pore structure and other instruments show that the specific surface area of the doped sample increases from 16.13 m²/g to 262.1 m²/g,and the proportion of Pd⁰ in the supported Pd increases from 56.49%to 70.44%,the Pd dispersion increases from 22.55%to 32.04%,and the Pd particle size decreases from4.96 nm to 3.48 nm,which jointly promote the improvement of the catalytic performance.The hydrogenation of acetone to methyl isobutyl ketone（MIBK）is a hydrogenation reaction catalyzed by the active sites of acid,alkali and metal.In this paper,HEDP and other precursors were used as phosphorus precursors,to copolymerize with urea and boric acid to prepare phosphorus-doped h-BN（BNP）,which was also loaded with Pd to construct a multifunctional catalyst.The results show that the performance of the BNP-supported Pd catalyst is significantly improved compared with the Pd/h-BN catalyst.On the catalyst Pd/BN（H）P-E-0.07 with the optimal P doping content,the acetone conversion rate reaches 58.24%,and the MIBK selectivity reaches 68.39%.On Pd/h-BN,the acetone conversion was only 1.02%,and MIBK was not detected in the reaction product.The instrumental characterization results show that P doping increases the specific surface area of h-BN from 909.67 m²/g to 1112.80 m²/g,and new surface groups N₂P=O and N₃P-OH appeared.These two groups have appropriate acidity and basicity,and together with palladium metal,catalyze the hydrogenation of acetone efficiently.The reason for the deactivation of the Pd catalyst in the acetone hydrogenation reaction was also studied in this paper.Using the characterization methods such as contact angle detection,it was found that the long-chain organic matter with high adsorption produced in the reaction covered the active site,and the oxygen-depleted organic matter was developed.The regeneration process of calcination restores the activity of the catalyst.