焙烧温度对CeO_2(ZrO_2)/TiO_2选择性催化脱硝性能的影响

采用溶胶-凝胶法并以不同温度焙烧制备一系列CeO_2(ZrO_2)/TiO_2(CZT)催化剂,考察了CZT催化剂固相结构、酸量、比表面积等性能与催化活性的关系。采用XRD、BET、NH3-TPD、H2-TPR以及XPS等表征技术对催化剂进行表征。结果表明:焙烧温度为450℃时CZT催化剂具有最高的催化活性,其在240~400℃的温度窗口内活性均高于90%,且具有较好的抗水和抗硫中毒能力。随着焙烧温度的提高,催化剂表面的Ce和Zr原子进入体相晶格且Ce0.5Zr0.5O2向Ce0.75Zr0.25O2转变,导致催化剂的储释氧能力和氧化还原性能降低。另外,锐钛矿和金红石型TiO_2晶粒尺寸的增加,催化剂的有效比表面积和总酸量降低,因此CZT催化活性随着焙烧温度的提高而有所降低。换言之,大的比表面积、良好的氧化还原性能、表面Ce4+的富集以及酸性位的增多均有利于NH3-SCR活性的提高。

EFFECT OF CALCINATION TEMPERATURE ON CATALYTIC PERFORMANCE OF CeO2(ZrO2)/TiO2 FOR SELECTIVE CATALYTIC REDUCTION OF NO BY NH3

A series of CeO2 (ZrO2)/TiO2 catalysts calcined at different temperatures from 450 ℃ to 750 ℃ were prepared by a sol-gel method,using for NH3-SCR of NO.Influence of calcination temperature on the solid phase structure,surface morphology,surface elements,specific surface area,redox properties and total acid amount of the catalysts were studied by techniques of XRD,XPS,N2-BET,H2-TPR and NH3-TPD.Results showed that CeO2 (ZrO2)/TiO2 calcined at 450 ℃ exhibited the best catalytic activity,N2 selectivity and anti-sulfur poisoning ability,and obtained more than 90％ NO conversion in a wide temperature range of 240 ～ 400 ℃ under GHSV of 80000 h-1.The maximum catalytic activity decreased with the increase of calcination temperature.With the increase of calcination temperature,the transfer of surface Ce and Zr into bulk lattice and the change from Ce0.5Zr0.5O2 to Ce0.75Zr0.25O2 could reduce redox properties and oxygen storage capacity.In addition,as the anatase-and rutile-TiO2 grain sizes increased,the effective specific surface area and the total acid amount decreased.Consequently the catalytic activity decreased with the increase of calcination temperature.The results implied that higher specific surface area,superior redox properties,more surface Ce4+ enrichment and more acidic sites were both conductive to obtain the excellent SCR activity.