| Among current technologies for controlling VOCs(Volatile organic compounds),catalytic combustion is a very attractive and widely used way due to its simple equipment requirement,low energy consumption,high efficiency,and without undesired byproducts such as NOx.And the catalyst is the key of catalytic combustion.Monolithic catalysts with honeycomb structure were developed in last decades.For this kind of catalyst,the cordierite honeycomb is usually used as the substrate and the washcoat is coated on its surface as the second support,then an active species such as Pt,Pd and Ru is deposited.At present,Al2O3 is usually used as the second support for the cordierite honeycomb due to its large specific surface area and the characteristic that it readily supports noble metals.However,the thermal stability of Al2O3 is poor,and Al2O3 easily reacts with the promoters to form spinel phases(AB2O4),which affects the performance of the catalyst.Therefore,the objective of this work is to develop a new washcoat to replace the conventional Al2O3 washcoat.In this study,prepared by an impregnation method,a novel CeO2-Y2O3 washcoat adhered onto the cordierite honeycomb substrate is developed.As Ce and Y containing no NO3- are used as precursors,this preparation technique of the washcoat is friendly to environment,and during the preparation,there are no deleterious emissions.Based on the high property of supported-Pd catalysts for VOCs catalytic combustion,the Pd monolithic catalysts supported by the CeO2-Y2O3 washcoat were prepared.The washcoats and their supported-Pd catalysts were characterized by XRD,Raman spectroscopy,H2-TPR,SEM,EDX and XRF techniques.Model reactions for the supported-Pd catalysts of CO, toluene,and ethyl acetate were carried out to evaluate the performance of the supported-Pd catalysts.The catalysts exhibited fairly good catalytic activity and thermal stability and are suitable for VOCs catalytic combustion.It is found that the CexY1-xO2-δwashcoats have better adhesion and higher vibration-resistance,and the cohesive ability increases with the increasing Y2O3 content.The CexY1-xO2-δwashcoats are suitable for preparing supported-Pd catalysts,and their adsorption efficiency of H2PdCl4 increases with the increasing Y2O3 content.By the model reactions of toluene over the Pd/CexY1-xO2-δcatalysts,it is found that the catalytic activities of Pd/CexY1-xO2-δcatalysts are closely related to the component of the washcoat,the Pd/Ce0.8Y0.2O2-δcatalyst exhibits the best activity and the catalytic activity increase with a rise in the Y2O3 content of the CexY1-xO2-δwashcoat.It can be concluded that the optimal component of the washcoat is Ce0.8Y0.2O2-δand the Pd/Ce0.8Y0.2O2-δcatalyst accordingly exhibits the best catalytic performance.The Pd/Ce0.8Y0.2O2-δcatalyst which possesses the best performance is detailedly researched and the effect of calcination temperature on the catalyst is studied.The Ce0.2Y0.8O2-δwashcoat has higher adsorption efficiency of H2PdCl4,which is probably related to the isoelectric point (IEP).The Pd/Ce0.2Y0.8O2-δcatalyst exhibits higher catalytic activity and better thermal stability for the combustion of VOCs,and the catalyst exhibits the best performance when the space velocity is lower than 25000 h-1.For the catalyst calcined at lower temperatures,the reodox property is better and the catalytic activity is higher.For the catalyst calcined at higher temperatures,the decline in the activity of the Pd/Ce0.2Y0.8O2-δcatalyst may be related to the increase in the mean crystallite size of PdO.The Ce0.2Y0.8O2-δwashcoat possesses excellent performance for the monolithic catalysts,and the preparation technique of the washcoat is friendly to environment.It is feasible and anticipated that the Ce0.2Y0.8O2-δ washcoat will replace the conventional Al2O3 washcoat.The catalysts supported by the washcoat hold high catalytic activity and thermal stability and are suitable for VOCs catalytic combustion.
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