Preparation Of Sulfur-doped Carbon Supported Ruthenium Alloy Catalysts For Selective Hydrogenation

In the last decades,supported alloyed noble catalysts have attracted many research interests and represent a hot research topic in the field of heterogeneous catalysis.Compared with monometallic noble metal catalysts,bimetallic noble metal alloy catalysts that have distinctly advantageous in regulating and optimizing the electronic structure/geometric configuration usually possess improved activity and selectivity.Besides,alloying noble metals with base metals can reduce the amount of noble metals to increase mass-based activity.As only the surface metal atoms directly participate in the catalysis process,the reduction the metal size to nanocluster scale(<2 nm)will maximize the exposure of surface-active metals and thus further improve the catalytic activity.However,the traditional wet-impregnation/high-temperature H2-reduction method frequently fails to prepare alloyed nanocluster catalysts,owing to the lack of strong metal-support interaction(SMSI),which leads to severe aggregation of metal species during the H2-reduction process.In this thesis,a general method is developed to prepare small-sized ruthenium-based alloy nanocluster catalysts with mesoporous sulfur-doped carbon(meso—SC)as the support based on the metal-support strong interaction.The performance of the prepared ruthenium-based alloy nanocluster catalysts in catalytic selective hydrogenation is also investigated.The main results can be summarized as follows:1.A general method is developed to synthesize supported ruthenium-based alloy nanocluster catalysts based on the metal-support strong interaction.With meso_SC as supports,five ruthenium-based alloy(Ru-M,M=Ga,In,Ge,Sn,Ni)nanocluster catalysts are prepared by simply impregnation of inorganic salt precursors onto the meso_SC supports and a following H2-reduction at high temperature.X-ray diffraction(XRD),transmission electron microscopy(TEM),and EDS line scanning characterizations confirm the alloy structures of the catalysts with average particle size of 1.02?1.24 nm.Based on the control synthesis with commercial carbon black as supports and the X-ray photoelectron spectroscopy(XPS)characterization analyses,it is concluded that the strong interaction between metal and the doped sulfur atoms in the meso_SC supports is crucial for inhibiting the aggregation of metal species during high temperature H2-reduction,which ensures the formation of small-sized alloy structures.2.The high catalytic performance of the prepared Ru-M nanocluster catalysts are demonstrated for the selective hydrogenation of quinoline and furfural.All the prepared Ru-M nanocluster alloy nanocluster catalysts show high catalytic activity for the hydrogenation of quinoline;and the Ru-Sn catalyst is the best among them.The turnover frequency(denoted as TOF)of meso_SC supported Ru-Sn(Ru-Sn/meso_SC)nanoclusters for the selective hydrogenation of quinoline and furfural reaches 2948 h-1 and 184 h-1.respectively;and the selectivity for both reactions is higher than 95%.The conversion and selectivity of Ru-Sn/meso_SC nanocluster catalyst for hydrogenation of 11 quinoline derivatives exceed 90%and 99%respectively,demonstrating the wide substrate applicability.After three cycles,the Ru-Sn/meso_SC nanocluster catalyst displays unchanged selectivity and slightly decreased conversion for quinoline hydrogenation,and almost unchanged selectivity and conversion for furfural hydrogenation.Based on the comparison with carbon black supported Ru-Sn alloy and,meso_SC supported monometallic ruthenium catalysts as well as the XPS analyses,the enhanced catalytic performance of the Ru-M nanocluster catalysts can be ascribed to the higher ratio of surface metal induced by the small size effect and the electron-deficient state of Ru induced by the SMSI and the alloying effect.