Synthesis And Characterization Of Supported Nano-Pt Catalysts For The Deep Oxidation Of VOCs

Volatile organic compounds(VOCs)are considered as a major class of pollutants emitted from chemical industries because they have harmful effects on human health and induce many environment problems.It has called for strict measures and environment regulations to be put in place.Among the various techniques for eliminating VOCs,catalytic combustion is identical as one of the most promising one because of its high efficiency,low energy consumption and low production of secondary pollutants.Supported noble metals especially platinum on Al2O3 catalysts are widely used for VOCs combustion.Although Pt/Al2O3 catalysts are highly active for the oxidation of VOCs,those catalysts are very expensive in the industrial field.So the development of catalysts presenting high catalytic behaviour with a small amount of noble metals has been paid great attention and the nano-sized Pt supported Al2O3 catalysts are strong desired.In this paper,a modified ethylene glycol(EG)reduction method was introduced to synthesize a serious of Pt/Al2O3 catalysts,and the catalytic performance of Pt/Al2O3 catalysts towards oxidation of benzene,ethyl actate and n-hexane were evaluated.Moreover,the influences of particle size of Pt,synthetic method,the difference of supports on the catalytic activity of Pt-catalysts towards oxidation of VOCs were studied.It is also further discussed that different Pt particles size sensitive effects of different pollutants.A range of characterizations,including HRTEM,CO chemisorption,CO-DRIFTS,ICP,XPS,H2-TPR,NH3-TPD and CO2-TPD were adopted to acquire more information about the relationship between their physical-chemical properties and the catalytic activity.Some specific conclusions from this work are listed as follows:1.A series of Pt/Al2O3 catalysts with different Pt nanoparticle sizes were prepared by means of modified EG reduction approach and tested for deep catalytic oxidation of benzene.The Pt average particle size decreases by raising pH values of the synthesis solution.The results also indicate that the Pt particle size exerts significant effect on the catalytic behavior.The decrease of the Pt particle size leads to the promotion of the ability of the catalysts to degrade benzene,which is attributed to more absorbed oxygen arising from higher dispersion of Pt.Moreover,it has been confirmed that the content of PtO species,which is regarded as active center for complete oxidation of benzene,is not the decisive factor in the process of benzene oxidation.The Pt/Al2O3-11 catalyst could convert benzene into H2O and CO2 completely at 145? and presents outstanding durability during the prolonged reaction time,whether in dry air or in the existence of CO2,cyclohexane or H2 O.2.A series of Pt/Al2O3 catalysts were prepared by L-method and R-method and then were calcined at different temperatures to assess their thermal stability.The catalytic behaviors of these catalysts for the abatement of benzene,ethyl acetate and n-hexane were also evaluated.The results show that the Pt/Al2O3 catalysts synthesized by L-method has enhanced interaction between Pt and Al2O3 compared with that of catalysts prepared by R-method,which lead to the formation of smaller Pt particles.The enhanced interaction existed in the L-catalysts also contributes to the formation of more adsorbed oxygen species and improve the reducibility of the catalysts,resulting in high catalytic activity for oxidation of benzene.It is concluded that L-method is a practical strategy to synthesize noble metal catalysts with high thermal stability.Moreover,the catalytic activity of Pt/Al2O3 catalyst for the completely oxidation of benzene and ethyl acetate decreases with Pt particle size becomes larger but the phenomenon is opposite for the oxidation of n-hexane.3.Catalytic performances for benzene,ethyl acetate,n-hexane over Pt-catalysts with different supports were evaluated.The results show that the sequence of catalytic activities of Pt-catalysts with various supports towards the oxidation of ethyl acetate is as follows:Pt/CeZr>Pt/ZSM-5>Pt/TiO2>Pt/Al2O3.This catalytic reaction depends on the synergistic effect of the acid sites and oxidizing sites.The acid sites of catalysts firstly promote the adsorption and dehydroxylation of ethyl acetate,and the high oxidizing ability is in favour of oxidizing the reactants.The order of catalytic performance of Pt-catalysts towards benzene and n-hexane are as follows:Pt/TiO2(Pt/CeZrOx)>Pt/Al2O3>Pt/ZSM-5.It can be seen that the oxidation of benzene and n-haxane is related to adsorbed oxygen species on the surface of catalysts.The catalysts with more adsorbed oxygen are likely to have enhanced catalytic performances.The content of Pt0 is related to acid-base property of catalysts,the content of Pt0 is higher with more stronge acidity or alkalinity of catalysts.