Study On The Synergy Of Au And Cu In Mercury-free Catalyst

The use of low-mercury catalysts in the production of vinyl chloride by acetylene hydrochlorination can partially alleviate the pressure of mercury pollution treatment in China,but the development of environmentally friendly mercury-free catalysts is still the future development direction of coal-based route acetylene hydrochlorination.The thesis aims at the urgent need to improve the stability of Au-Cu/AC mercury-free catalysts.From the perspective of increasing the content and stability of the active components of Au(Ⅲ)and Au(Ⅰ),the AuCu/AC catalyst was synergistically stabilized by modification of the carrier and valence state control of the auxiliary metal Cu.First,the reaction activity of the prepared Au-Cu/AC catalyst was evaluated under laboratory conditions,and the influence of the ratio of Au and Cu on the conversion of acetylene and the yield of vinyl chloride was investigated.By adjusting the loading of Au and Cu,the suitable loading ratio of active components is determined to be Au:Cu=0.4wt%:2.5wt%,the conversion rate of acetylene reaches about 92.5%,the selectivity of vinyl chloride is kept at about 99%.The addition of auxiliary metal Cu can effectively improve the dispersion of Au on the carrier and reduce the loading of Au.Then,the coconut shell activated carbon used as a carrier was modified with nitrogen and oxygen,and the influence of the nitrogen-containing and oxygen-containing functional groups on the stability of Au(Ⅲ)and Au(Ⅰ)in the catalyst was investigated.The results of nitrogen modification with melamine show that N-pyridine can provide a suitable anchor point for Au(Ⅲ),which is beneficial to improve the stability of Au(Ⅲ),and the suitable calcination temperature is 600℃.The content of N-pyridine increased by 16.2%,the content of Au(Ⅲ)reached 80.5%,the conversion rate of acetylene was up to 93%,and the reaction selectivity was stable above 99%.Oxygen modification of activated carbon using nitric acid.Compared with unmodified activated carbon,the content of phenolic hydroxyl group increased from 35,6%to 59.2%,the content of carboxyl group increased from 6.5%to 15.9%,the content of lactone group decreased from 40.5%to 7.8%,and the carbonyl content did not change much.Oxygencontaining functional groups can increase the dispersion of the surface active components of the catalyst,thereby improving the performance of the catalyst,the highest acetylene conversion rate can reach 96.7%.Finally,by adjusting the valence state of the supported Cu during the catalyst preparation process,the influence of the change of the valence state of Cu on the stability of Au(Ⅲ)and Au(Ⅰ)was investigated.The results show that after 12 hours of acetylene hydrochlorination,The content of Au(Ⅰ)in Au-Cu(Ⅰ)/AC was increased from 33.2%to 35.1%,and Cu(Ⅰ)kept the content of Au(Ⅰ)at about 35%,which inhibited the reduction of Au ions;The content of Au(Ⅰ)in Au-Cu(Ⅱ)/AC increased from 15.7%to 23.5%,and Cu(Ⅱ)was partially reduced to Cu(Ⅰ)in the reaction,which also played a role in stabilizing the content of Au(Ⅰ);The content of Au(Ⅰ)in Au-Cu(0)/AC decreased from 23.7%to 8.2%,and Cu(0)promoted the reduction of Au(Ⅲ)and Au(Ⅰ)active centers.The research results enrich the mechanism of Au-Cu synergistic stabilization of gold-based mercury-free catalysts,and provide data references for promoting the application of mercury-free catalysts in actual industrial production.