CAJ | 학술논문

采用多种物理化学手段研究了不同负载量V2O5/TiO2催化剂的VOx物种分散状态、表面酸性、可还原性及其选择性催化还原(SCR) NO性能.结果表明,V2O5在锐钛矿TiO2表面的实测单层分散容量约为1.14 mmolV/100 m2 TiO2,与“嵌入模型”的估算值相符,表明分散态的钒离子应键合在TiO2表面的八面体空位上.随着V2O5负载量的增加,V2O5/TiO2催化剂上NO转化频率(TOF)先急剧增加,至0.70 mmolV/100 m2 TiO2(略超过分散容量的一半)时达到极大(约8.3×l0-3 s-1),然后又急剧下降；同时,孤立VOx 物种可能倾向于分散在相邻的八面体空位上,且通过V-O-V化学键相连形成聚合的VOx 物种,V-O-V键所占比例增加而V-O-Ti键所占比例减小,催化剂表面单位钒离子的Br(o)nsted 酸中心量增加,故催化剂的 TOF 急剧增加.随着负载量进一步增加,虽然催化剂表面单位钒离子的Br(o)nsted酸中心量仍缓慢增加,但V-O-Ti键所占比例减少,导致钒离子的可还原性下降,另外,分散容量以上时晶相V2O5的形成也导致钒离子表面利用率下降,从而导致催化剂的TOF下降.桥式Br(o)nsted酸位(V-O(H)-V)也是SCR反应活性中心之一,不同负载量V2O5/TiO2催化剂上SCR活性与表面VOx物种的分散状态、表面酸性和钒离子可还原性密切相关.
채용다충물이화학수단연구료불동부재량V2O5/TiO2최화제적VOx물충분산상태、표면산성、가환원성급기선택성최화환원(SCR) NO성능.결과표명,V2O5재예태광TiO2표면적실측단층분산용량약위1.14 mmolV/100 m2 TiO2,여“감입모형”적고산치상부,표명분산태적범리자응건합재TiO2표면적팔면체공위상.수착V2O5부재량적증가,V2O5/TiO2최화제상NO전화빈솔(TOF)선급극증가,지0.70 mmolV/100 m2 TiO2(략초과분산용량적일반)시체도겁대(약8.3×l0-3 s-1),연후우급극하강；동시,고립VOx 물충가능경향우분산재상린적팔면체공위상,차통과V-O-V화학건상련형성취합적VOx 물충,V-O-V건소점비례증가이V-O-Ti건소점비례감소,최화제표면단위범리자적Br(o)nsted 산중심량증가,고최화제적 TOF 급극증가.수착부재량진일보증가,수연최화제표면단위범리자적Br(o)nsted산중심량잉완만증가,단V-O-Ti건소점비례감소,도치범리자적가환원성하강,령외,분산용량이상시정상V2O5적형성야도치범리자표면이용솔하강,종이도치최화제적TOF하강.교식Br(o)nsted산위(V-O(H)-V)야시SCR반응활성중심지일,불동부재량V2O5/TiO2최화제상SCR활성여표면VOx물충적분산상태、표면산성화범리자가환원성밀절상관.
The effect of the dispersion state and surface properties of supported vanadia on the selective catalytic reduction (SCR) activity of NO over V2O5/TiO2 catalysts was studied by various experimental techniques.The experimental monolayer dispersion capacity of V2O5 on anatase (6.86 VOx/nm2) measured by XRD was almost the same as the concentration of surface vacant sites of anatase estimated by the incorporation model,and it was suggested that isolated vanadia species tend to be dispersed on adjacent octahedral vacant sites.An increase of the NO turnover frequency (TOF) at 300 ℃ to a maximum (8.3 × 10 3 s-1) at a coverage near half a monolayer was related to the increase of the amount of weak acid sites (Br(o)nsted acid site on each vanadium ion).The TOF decreased rapidly at high VOx coverages because of a decrease of the reducibility of vanadia species and a decrease of the ratio of exposed vanadia species on the surface.The Br(o)nsted acid sites on bridging V-O(H)-V and terminal V-OH of polymeric vanadia species were all active sites in the SCR reaction.The SCR activity of the V2O5/TiO2 catalysts was related to the dispersion state,acidity,and reducibility of the vanadia species.