Different roles of MoO_(3)and Nb_(2)O_(5)promotion in short-chain alkane combustion over Pt/ZrO_(2)catalysts  

MoO_(3)和Nb_(2)O_(5)助剂对Pt/ZrO_(2)催化剂上短链烷烃燃烧反应的不同促进作用

作　　者：Bingheng Cen Cen Tang Jiqing Lu Jian Chen Mengfei Luo 岑丙横;汤岑;鲁继青;陈建;罗孟飞(浙江师范大学物理化学研究所,先进催化材料教育部重点实验室,浙江省固体表面反应化学重点实验室,浙江金华321004)

机构地区：[1]Key Laboratory of the Ministry of Education for Advanced Catalysis Materials,Zhejiang Key Laboratory for Reactive Chemistry on Solid Surfaces,Institute of Physical Chemistry,Zhejiang Normal University,Jinhua 321004,Zhejiang,China

出　　处：《Chinese Journal of Catalysis》2021年第12期2287-2295,共9页催化学报（英文）

基　　金：国家自然科学基金面上项目(21872124,22072137).

摘　　要：Pt/ZrO_(2)catalysts promoted with MoO_(3)and Nb_(2)O_(5)were tested for the combustion of short-chain alkanes(namely,methane,ethane,propane,and n-hexane).For short-chain alkane combustion,the inhibition of MoO_(3)(for the methane reaction)dramatically transformed to promotion(for the ethane,propane,and n-hexane reactions)as the carbon chain length increased,whereas the remarkable promotion of Nb_(2)O_(5)gradually weakened with an increase in the carbon chain length.Based on a detailed study of the oxidation reactions of methane and propane over the catalysts,the different roles of the promoters in the reactions were ascribed to differences in the acidic properties of the surface and the oxidation or reduction states of the Pt species.The MoO_(3)promoter could decorate the surface of the Pt species for a Pt-Mo/ZrO_(2)catalyst,whereas the Nb_(2)O_(5)promoter on the support could be partially covered by Pt particles for a Pt-Nb/ZrO_(2)catalyst.The formation of accessible Pt-MoO_(3)interfacial sites,a high concentration of metallic Pt species,and a high surface acidity in Pt-Mo/ZrO_(2)were responsible for the enhanced activity for catalytic propane combustion.The lack of enough accessible Pt-Nb_(2)O_(5)interfacial sites but an enhanced surface acid sites in Pt-Nb/ZrO_(2)explained the slight improvement in activity for catalytic propane combustion.However,the stabilized Pt^(n+)species in Pt-Nb/ZrO_(2)were responsible for the much-improved activity for methane combustion,whereas the Pt^(n+)species in Pt-Mo/ZrO_(2)could be reduced during the oxidation reaction,and the fewer exposed surface Pt species because of MoO_(3)decoration accounted for the inhibited activity for methane combustion.In addition,it can be concluded that MoO_(3)promotion is favorable for the activation of C-C bonds,whereas Nb_(2)O_(5)promotion is more beneficial for the activation of C-H bonds with high energy.贵金属Pt催化剂具有高活性和热稳定性,广泛应用于催化挥发性有机物的完全氧化反应(燃烧反应).短链烷烃(甲烷、乙烷、丙烷等)化学性质稳定,是最难氧化的一类有机物,常用作考察燃烧反应催化剂性能的模型反应物.然而,目前报道的研究工作通常仅限于针对某一种烷烃底物的催化燃烧,系统考察催化剂以及助剂对不同短链烷烃的催化燃烧活性鲜有报道.在短链烷烃中,甲烷只有C–H键;而其它烷烃除了C–H键;还有C–C键.因此,研究催化剂对甲烷、乙烷和丙烷燃烧反应催化性能的差异性,对于认识催化剂上C–H键和C–C键的活化具有非常重要的意义.本文制备了MoO_(3)或Nb_(2)O_(5)修饰的Pt/ZrO_(2)催化剂并用于短链烷烃的燃烧反应.研究发现,MoO_(3)助剂对甲烷燃烧有明显的抑制作用,但对乙烷,丙烷和正己烷燃烧反应具有促进作用,促进作用随着烷烃碳链的增长逐渐增加;Nb_(2)O_(5)助剂对甲烷、乙烷、丙烷和正己烷燃烧反应均具有促进作用,然而促进作用随着碳链的增长而逐渐减弱.MoO_(3)和Nb_(2)O_(5)助剂的不同促进作用与助剂影响催化剂表面酸性以及Pt物种的氧化或还原态有关.NH_(3)-TPD结果表明,MoO_(3)助剂可以显著增加Pt/ZrO_(2)催化剂表面强酸位点数量,而Nb_(2)O_(5)助剂可以显著增加Pt/ZrO_(2)催化剂表面中强酸位点数量.HTEM结果表明,两种助剂的添加都不会明显改变Pt物种的颗粒尺寸.在Pt-Mo/ZrO_(2)催化剂上,MoO_(3)覆盖部分Pt物种形成丰富的Pt-MoO_(3)界面,促进了金属Pt物种和强表面酸性位点的生成,提高了丙烷燃烧反应活性;Pt-Nb/ZrO_(2)催化剂上载体表面的部分Nb_(2)O_(5)被Pt物种包覆,使得生成的表面Pt-Nb_(2)O_(5)界面低于Pt-Mo/ZrO_(2)催化剂,但由于催化剂表面酸性位的提升,也促进了丙烷燃烧反应活性的提高.XPS结果表明,在甲烷燃烧反应中,Pt-Nb/ZrO_(2)催化剂上Pt^(n+)物种能够更加稳定地存�

关 键 词：Pt/ZrO_(2)catalyst Alkanes combustion MoO_(3)promoter Nb_(2)O_(5)promoter Active site 

分 类 号：TQ426[化学工程] X701[环境科学与工程—环境工程]