Al-doped TiO₂ Mesoporous Material Supported Pd With Enhanced Catalytic Activity For Complete Oxidation Of Ethanol

It is of strategic significance for remising both energy crisis and air environmental pollution to spread the application of ethanol-gasoline.And for the rigorous automobile emission standards,traditional three-way catalyst can no longer meet increased demands.The modification or development of new catalyst to remove exhaust gas emission based on the relation between catalyst structure and physicochemical properties and the reaction of volatile organic compounds?VOCs?removal have been considered to be hot topics in the field of catalytic chemistry,materialogy,environment and energy science.Pd/TiO₂ catalyst has been demonstrated of highly efficiency for catalytic elimination of VOCs and of wide application prospect in atmospheric pollution control for its higher activity and less expensive compared with other precious metals based TiO₂ catalyst.While for the fact that commercial nano TiO₂ which possess lower BET specific surface area and easier access to transform phase could result in lower dispersion of surface active compounds and poor thermal stability,TiO₂ modification has become a way to change its morphology and surface property thus enhance catalytic performance of TiO₂ supported catalyst.Currently,it is of scientific and practical value to adopt proper method to modify TiO₂ and investigate the internal relation between catalyst and catalytic activity of ethanol oxidation over the novel catalyst.Based on all mentioned above,we prepared Al-doped TiO₂ mesoporous materials by EISA and Al³⁺ was found to enter lattice of TiO₂ to form defect TiO₂.Next a series of Pd loaded Al-doped TiO₂ were synthesized and tested for total oxidation of ethanol.Then transition metal Ce was introduced to further improve catalytic performance and their catalytic performance of ethanol oxidation at the conditions of rich-oxygen and lean-oxygen were deliberated.In the present work,at first,Al-doped TiO₂ mesoporous materials were synthesized followed solvent-evaporation induced self-assembly?EISA?and applied P123 as template,tetrabutyl titanate as Ti precursor,aluminium isopropoxide as Al precursor,1-butanol as solvent.The BET specific surface area of Al-doped TiO₂ mesoporous material was 159 m2g-1,and its pore volume and pore size were 0.14 cm-3g-1 and 4.28 nm,respectively.The results revealed that Al3+ doped lattice of TiO₂ to form defect TiO₂ and abundant oxygen was adsorbed on defected TiO₂.Then,A series of Pd catalyst with Al-doped TiO₂ mesoporous material were prepared by impregnation method and the influence of Al dopant on ethanol oxidation were discussed.Results showed that catalytic performance of ethanol oxidation over Pd/xAT-500 was better than that over Pd/T-500,while there was no liner relationship between the amount of Al dopant and catalytic activity.Pd/7.5AT-500 possessed outstanding activity.At the temperature of 200?,TOF of ethanol conversion over Pd/7.5AT-500 was 1.62 s-1 and the TOF of CO₂ yield reached 3.17 s-1,which revealed that the higher ethanol oxidation and CO₂ production from ethanol oxidation per unit time on per active site were achieved on Pd/7.5AT-500.Characterization measures were carried out to study morphology,chemical state of Pd species,atom ratios of surface elements.Results showed that Pd/7.5AT-500 catalyst possessed higher surface area,pore size and pore volume and Pd dispersion than Pd/T-500,and the introduction of Al enhanced mesoporous architecture and surface properties.In the catalyst Pd/7.5AT-500,the chemical state of Pd species were Pd²⁺ and Pd⁴⁺ while Pd in Pd/T were mainly in Pd0 and Pd²⁺.In addition,due to the presence of defect TiO₂,ratio of adsorbed oxygen /surface oxygen species of Pd/7.5AT-500 was 5 times higher than that of Pd/T-500.Meanwhile,Al dopants were found to restrain phase transformation of TiO₂ from anatase to rutile and enhanced stabilized anatase,suppressed SMSI between Pd and TiO₂ and improved the reducibility of Pd species.The main reason to the superior ethanol oxidation activity over Pd/7.5AT-500 was oxidized Pd with higher reducibility and enrichment oxygen in defect TiO₂.At last,transition metal Ce was introduced by co-impregnation method to further modify Pd/AT.Activity evaluation in rich-oxygen presented that Pd-Ce/AT had better catalytic performance of deep oxidation of ethanol.Total conversion of ethanol was achieved and the CO₂ yield was over 85% at temperature of 250?,which was lower than that of Pd/AT.This could be attributed be Pd oxides and rich adsorbed oxygen.At lean-oxygen condition,Pd-Ce/AT was efficient for ethanol conversion while not for CO₂ yield.The main product was CO and acetaldehyde at the lack of oxygen,while its higher ethanol conversion was due to surface active sites that induced first step of ethanol oxidation.More abundant lattice oxygen in CeO₂ and oxygen release capacity of CeO₂ should be the main factors for higher ethanol oxidation activity over pure Ce catalyst at lean oxygen condition.