Anti-poisoning Performance And Mechanism Of Supported Cerium-Tin Metal Oxide DeNO_x Catalyst

As one of the typical pollutants in the atmosphere,nitrogen oxides have brought many environmental problems,such as acid rain,PM2.5,photochemical smog and so on.Therefore,it is of great significance to control the emission of nitrogen oxides.NH3-SCR(ammonia-selective catalytic reduction)is considered to be the most effective technology for the purification of nitrogen oxides at present,and the most important factor in NH3-SCR is its catalyst.Nowadays,the most widely used SCR catalyst is VWT catalyst,which has high activity and mechanical strength,but it also has some problems,such as low selectivity at high temperature,poor anti-toxicity and so on.Besisdes,in addition to NOx,there are often alkali(alkali-earth)metals and heavy metals in flue gas,which will cause catalyst poisoning and deactivation.Therefore,the development of highly active and highly toxic-resistant catalysts,and in-depth exploration of its mechanism is the focus of the current research on de NOx.In this paper,a highly effective anti-poisoning titanium dioxide solid superacid catalyst was designed and developed.The practical application prospects of the catalyst were investigated,and its anti-poisoning mechanism was studied by means of various characterization methods.The content of this paper is as follows:(1)A titanium dioxide superacid catalyst was prepared by hydrothermal and impregnation.The performance of the catalyst was tested to evaluate its performance.It was found that the catalyst not only has good activity at low temperature,wide temperature window,high nitrogen selectivity,good stability,but also can maintain excellent catalytic performance at very high space speed.In addition,the catalyst also has good properties of alkali / alkaline earth metal resistance,heavy metal resistance,and H2 O & SO2 resistance.(2)In order to explore the reasons for the excellent alkali resistance of cerium-tin bimetallic oxide catalysts supported by titanium dioxide solid superacid,unsulfurized titanium dioxide was prepared as a carrier with the same proportion of cerium oxide and tin oxide as a comparison.Through a series of characterization,it is found that titanium dioxide solid superacid as a carrier will greatly improve the acidity of the catalyst,although alkali metals will consume the acidity of the catalyst,but due to the existence of superacid sites in solid superacid,will be preferentially consumed,so as to protect other acidic sites,so that the activity of the catalyst can be maintained.When titanium dioxide is used as the carrier,the Br ? nsted acid sites on the catalyst surface are first consumed,and then the Lewis acid sites are consumed,so that there are not enough acid sites on the catalyst surface for the acid cycle in the SCR reaction,resulting in the deactivation of the catalyst.(3)There are not only alkali metals but also heavy metals in flue gas.Titanium dioxide and solid superacid as carriers can resist the toxicity of alkali metals and heavy metals at the same time.It is found that both alkali and heavy metals will consume a large amount of acidic sites on the surface of the catalyst.The existence of alkali metals will have a negative effect on the redox of the catalyst,while heavy metals will promote the redox of the catalyst to a certain extent.When the two coexist,in the cerium-tin bimetallic oxide catalyst supported by titanium dioxide solid superacid,the promotion of heavy metals occupies a dominant position,so that the redox behavior of the catalyst can be maintained.In addition,through the exploration of the reaction mechanism of the catalyst,it was found that the presence of alkali metals or / and heavy metals could weaken the bonding between Ti-O bond and sulfate in the solid superacid of titanium dioxide and induce the migration of sulfate in the bulk phase of the catalyst to the surface.Alkali metals and heavy metals deposited on the surface of the catalyst will preferentially combine with sulfate,so as to avoid the damage of these toxic substances to the surface active sites of the catalyst and achieve the purpose of anti-toxicity.