Research On The Controllable Preparation And Hydrogenation Performance Of Supported Noble Metal Catalysts

Catalysis occupies an extremely important position in the modern chemical industry.Reasonable design and accurate preparation of high-performance nano-catalysts to achieve high-efficiency catalysis selectively has always been the goal pursued by people.Although important progress has been made with the rapid development of synthetic chemistry,the understanding of the internal relationship between the composition,structure and performance of the catalyst is still relatively limited.In this thesis,the selective hydrogenation of phenol and the hydroformylation of styrene were chosen as the research objects.The catalysts supported with Pt nanoclusters and Rh single site were designed and constructed,respectively.The internal relationship between the composition,structure and performance of the catalysts are studied under different reaction conditions,and then the compositions of the catalysts are optimized to achieve efficient and selective catalysis.The specific research results are summarized as follows:(1)A rapid solid solution annealing strategy(thermal explosion method)was developed to prepare supported metal nanoclusters catalysts.At high temperature,the aqueous solution of metal precursor(H2PtCl6)and TiO2 nanocrystals(Degussa P25)can be solid-solution annealed directly and rapidly to prepare Pt Cs/TiO2 catalysts with Pt cluster dispersed uniformly on TiO2 carrier,and the Pt clusters existed in mixed valence states of Pt4+and Pt2+.The catalyst was used to catalyze the selective hydrogenation of phenol at ambient temperature and pressure,and when the phenol was converted totally,100%selectivity to cyclohexanol and cyclohexanone(KA oil)was obtained.The ratio of K/A can be controlled effectively by the reaction time.Stability experiments showed that the catalytic activity can be well maintained after five consecutive reactions.When phenol derivatives were used as substrates,corresponding ketones and alcohols were also prepared with high selectivity.The thermal explosion method was further extended to the synthesis of other clusters.It is found that,using different supports and metal precursors,supported nanocluster catalysts,such as Pt Cs/Al2O3,Pt Cs/CeO2,Pd Cs/TiO2,Ru Cs/TiO2,Co Cs/TiO2,Fe Cs/TiO2,Cu Cs/TiO2 can also be prepared,which proved the universality of this strategy.(2)A post-modification method was developed to prepare single metal site catalysts.Firstly,1,10-phenanthroline-3,8-dicarboxylic acid(PhenDC)was synthesized controllable,and the N atoms on the phenanthroline were used to graft monometallic site.The UiO-67-Phen was prepared with mixed ligand,PhenDC and 4,4’-biphenyl acid(BPDC),and zirconium oxychloride under solvothermal conditions.Then,the UiO-67-Phen was modified by Rh(CO)2(acac)(acac=acetylacetone)to prepare the single metal Rh catalyst,UiO-67-Phen-Rh.The catalyst was used to catalyze the hydroformylation of styrene at 80℃,2 MPa CO and 2 MPa H2.When the conversion rate of styrene was 92%,the selectivity of corresponding linear and branched aldehyde was 100%,and the ratio of linear to branched aldehyde was 32:68.The catalyst did not deactivated significantly after four cycles of reaction,indicating that the single-metal Rh catalyst has good stability.The research works mentioned above may provide new ideas and new methods for the design and precise preparation of catalysts,and help to solve some catalytic problems.