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.