Mechanism Study Of Interfacial Effect On The Metal Oxides Catalysts For The Catalytic VOCs Combustion

In recent years,the emission of volatile organic compounds(VOCs)in China has remained high,which causes damage to human health,and the catalytic combustion technology is one of the most efficient means to curb its pollution.The core of the catalytic combustion is the design of catalysts with high activity and high stability.Heterostructured interfaces provide catalysts with new physicochemical properties,at which the defect structures directly affect the structure,activity,and reaction pathways of catalysts.Therefore,this thesis aimed to design novel catalysts with heterostructured interface.We investigated efficient synthesis methods for the nanohybrid "AB2O4@MOx" catalysts and the effect of temperature-dependent acid site.Subsequently,the strong metal-support interaction was achieved by using the heterostructured interface as a carrier and supporting Pd2+single atom.Based on this,we successfully developed the highly active catalysts with heterostructured interface for the catalytic VOCs(toluene and propane)combustion.The results obtained are as follows:Effect of heterostructured interface of the LDHs-derived non-noble metal catalysts:Based on the uniform distribution of divalent and trivalent metal cations in the layered double hydroxides(LDHs)layers,we synthesized nanohybrid "AB2O4@MOx" catalysts(non-noble metal),realizing the spinel(AB2O4)and oxide(MOx)combined on the nanoscale.The activity and reaction rates of the "AB2O4@MOx"catalysts with a broad interface were significantly higher than those of the physically mixed"AB2O4+MOx"catalysts.Severe lattice fringe blurring and lattice distortion appeared near the interface,which indicated that the strong interfacial interaction was favorable for the generation of defect structures,thus increasing the catalytic activity.Optimization effect of heterostructured interface of the non-noble metal catalysts:Co cations were selectively doped into the AB2O4 lattice and occupied the A and B sites,but the MOx species of the"AB2O4@MOx" catalyst were not affected in this process.The main effects of A&B-sites Co were as follows:At 200℃,the Br?nsted acid sites were significantly enriched,and the adsorption capacity of the catalyst surface for propane was enhanced;At 350℃,the Cu-O bond was weakened,which promoted the generation of oxygen vacancies and enriched Lewis acid sites.At the same time,the formation energy of oxygen vacancies was significantly reduced.In addition,the difference in ionic radius between the doped Co cations and the original cations led to lattice distortion of the AB2O4 phase,which promoted the formation of defect structures.Effect of heterostructured interface of the noble metal catalysts prepared by acid etching method:"AB2O4@MOx" catalysts(noble metal)were synthesized by an acid etching method.The Pd2+single atoms were anchored on the lattice of AB2O4 and MOx,and its anchoring promoted the generation of oxygen vacancies.The electron energy loss spectrum showed that:comparing the interface with the AB2O4 phase,there was redundant coordination oxygen at the interface,and the redundant coordination oxygen possessed higher lattice oxygen activity,which was beneficial to the deep oxidation of VOCs;compared with MOx species,there were abundant oxygen vacancies at the interface,which was conducive to the adsorption and dissociation of gas-phase O2,thereby improving the low-temperature performance of the catalytic VOCs combustion.Structure-activity mechanism and reaction routes of heterostructured interface of the noble metal catalysts:There was a strong metal-support interaction between the Pd2+ single atoms and "AB2O4@MOx" support:the interface promoted the generation of distorted Pd1O4,which could be reduced to Pd1O3 at room temperature.Pd1O3 could then activate gas-phase O2 to form PdiO5,thereby achieving efficient catalytic combustion of CO at room temperature;the native oxygen vacancies on the support reduced the oxygen coordination number of Pd2+single atoms,inducing the formation of Pd1O3;the distorted Pd1O4,Pd1O3,and Pd1O5 enhanced the lattice oxygen mobility of the "AB2O4@MOx" support,thereby realizing the efficient catalytic combustion of toluene.