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Ethylene is the basic material in petroleum chemical industry and the removal of the small amounts of acetylene existed in the feedstocks is an important part of the ethylene processing procedures.Selective hydrogenation of acetylene using catalysts is a widely used method to remove the acetylene,and palladium is the commonly used catalyst in the industry.In this study,atomic layer deposition(ALD)was used to deposit TiO2 and Pd particles on the MCM-41 mesoporous molecular sieve respectively,to produce the active catalyst which has high specific surface area and highly dispersed Pd nanoparticles,incipient wetness impregnation was also used to deposition Pd on subustrasts as a comparison.The results are detailed as follows: 1.Pd/TiO2/MCM-41 catalysts was synthesized by ALD.The obtained Pd/TiO2/MCM-41 series catalysts,Compared with the catalysts prepared by incipient wentness impregnation,show higher activity due to the highly dispersed Pd nanoparticles and have better activity and comparable selectivity compared with previously reported Pd/TiO2 system.2.The catalytic performance dependence on the amount of deposited TiO2 was investigated,and the results show a large amount of deposited TiO2 leads to a decreased acetylene conversion,whereas the selectivity of ethylene was increased.3.The effect of the assembling between TiO2 and Pd nanoparticles on the catalytic properties of Pd/TiO2/MCM-41 catalysts was studied.The results show that the selectivity of Pd catalyst was greatly improved by depositing TiO2 as assistant catalyst on the surface of Pd particles,and the catalytic efficiency can be preserved after the reduction annealing.4.The as-prepared catalysts were annealed in hydrogen ambient at 300 ℃ and 500 ℃ respectively to introduce the SMSI,which can improve the selectivity of the catalyst.The results show that SMSI was introduced by partially reducing TiO2 after 500 ℃ annealing.In the same series,the catalysts reduced at 500 ℃ exhibits lower conversion as compared to that of the catalysts reduced at 300 ℃,while the selectivity of catalyst at 500 ℃ was higher.