Fabrication And Control Of PtSn Nanocatalysts Toward Hydrogenation Of Acetic Acid

The difficulty in the hydrogenation of acetic acid to ethanol is the development of high performance hydrogenation catalysts.Precious metals,especially Pt and Pd,are ideal acetic acid hydrogenation catalysts.How to further increase the utilization efficiency of precious metal catalysts is always a big challenge.This dissertation focuses on the controlled preparation of highly efficient PtSn bimetallic nanocatalysts and their structure-activity relationships.Sn-supported,N-doped hollow silica sphere（Sn/NHSS）was successfully prepared by emulsion-micelle dual templating route（EM）,and a novel PtSn/NHSS catalyst was prepared by electrostatic adsorption method（SEA）and for the first time applied in the acetic acid hydrogenation.The 0.5Pt1Sn/NHSS（A1.0-E70）catalyst prepared by APTES/OA=1.0 and EtOH/OA=70 is the best catalyst,and the catalytic activity was1.3 times that of 0.5Pt1Sn/SiO₂ catalyst prepared by the modified two-step sol-gel method（MTSG）.The mechanism of nitrogen on PtSn catalyst was investigated by maintaining the same Pt and Sn loadings.Compared with 0.5Pt1Sn/N-SiO₂ prepared by the post-treatment by APTES,N on 0.5Pt1Sn/NHSS catalyst was highly dispersed.During the reduction of the catalyst,the electrons of Pt shifted to nitrogen,causing a strong interaction between the platinum and nitrogen,inhibiting the aggregation of Pt clusters.Thus,the dispersion of Pt on the support was greatly improved.More exposed Pt sites could activate more hydrogen,thereby achieving high acetic acid conversion（86.6%）and ethanol selectivity（90%）as well as the specific activity of 0.5Pt1Sn/NHSS is about1.3 times that of the 0.5Pt1Sn/SiO₂ catalyst.The N-doping method by APTES post-treatment leads to an uneven dispersion of nitrogen in the form of-NH₂,which could not have a strong interaction with Pt.Therefore,this kind of N dopant gave no prompt effect on the dispersion of Pt.The effects of non-noble metal promoters on catalytic activity were investigated.The Fe and Co promoted catalysts exhibited no effect on the activity of acetic acid hydrogenation.At the same time,other metal promoters such as Cu,Zn,Mn and Ce have been found to be not conducive to acetic acid hydrogenation.However,the addition of Ni can greatly improve the activity of PtSn catalyst,and the Ni-doped catalyst prepared by incipient-wetness impregnation method（IW）presented higher catalytic activity than that prepared by sol-gel（SG）method.During the loading of Ni by sol-gel method,Ni can enter the SiO₂ framework to form a Ni-Si spinel structure.The strong interaction between Ni and Si made it fairly difficult for the reduction of Ni species.The influence of Ni on the nature of PtSn catalytic was revealled.With the increase of Ni content,the catalytic activity first increased and then decreased.the catalyst with0.1%Ni exhibited the best reaction activity,and its space time yield（STY）is about twice that of the PtSn/SiO₂ catalyst.On the one hand,a small amount of Ni has strong interaction with Pt to provide hydrogen enriched environment and increase the ability to activate hydrogen.On the other hand,Ni promotes the dispersion of platinum,giving more exposed active sites for H₂ activation.However,higher Ni content might cover the surface hydroxyl groups and silyl hydroxyl groups of the support,resulting in a weaker interaction between the platinum and the support as well as a lower Pt dispersion.