Preparation Of Pure Phase ZrO₂ And Selective Hydrogenation Of Phenol To Cyclohexanone Over Pd/ZrO₂

ZrO₂ simultaneously having acidity,alkaline,oxidation and reductive,is widely used for different types of catalytic reactions as catalyst or catalyst support.In the catalytic reaction which ZrO₂ participates in,monoclinic and tetragonal structure of ZrO₂ is most commonly used and often significantly influence the activity and selectivity of the reaction.It is important to prepare ZrO₂ with pure phase which is applied to catalytic reaction.Cyclohexanone is an important raw materials for organic chemical,mainly for the synthesis of intermediates of caprolactam,adipic acid,salts and fine chemical products.Selective hydrogenation of phenol to cyclohexanone have a high selectivity and low energy consumption.In this paper,ionic liquid as template,the pure phase ZrO₂ prepared by sol-gel method was used for preparation of Pd/ZrO₂catalyst and evaluated on performance of selective hydrogenation of phenol to cyclohexanone.Firstly,the pure monoclinic ZrO₂（m-ZrO₂）was obtained by sol-gel method templated by ionic liquid and ZrO₂ prepared by traditional sol-gel method was the mixed phases including monoclinic and tetragonal phase.The type and amount of ionic liquids and pH in the reaction system were studied to observe the effects on crystal and morphology of ZrO2,etc.It was found that the formation of m-ZrO2nuclear was easily induced by antion BF₄^-in ionic liquid[bmim]BF₄ which had a stronger coordination ability,and[bmim]BF4 was preferential adsorbed on the（-111）m and（111）m planes of m-ZrO2 nuclear which could reduce surface energy and inhibit their growing,eventually developed nanosheet of ZrO₂.However anion HSO₄^-having a weaker ability to coordinate or form hydrogen bonds wound induce the formation of t-ZrO2 nuclear which eventually developed particles.Secondly,catalyst Pd/m-ZrO₂ was preparaed by the pure monoclinic ZrO₂supported Pd and studied its catalytic activity on selective hydrogenation of phenol to cyclohexanone reaction.Under reaction conditions as following:20 mL aqueous solution of phenol（0.25 mol/L）,a catalyst-to-aqueous solution of phenol 0.04 g/mL,140℃,30 min,P（H₂）=1.0 MPa,phenol conversion was 90.3%and the selectivity of cyclohexanone was 73.9%.When Pd/t-ZrO₂ was used for the selective hydrogenation of phenol,phenol conversion and cyclohexanone selectivity respectively was 100%and 53.3%.The aqueous layer on m-ZrO₂ which enriched-OH was easily formed and contributed to desorption of cyclohexanone which avoided depth hydrogenation to cyclohexanol.Meanwhile,the presence of aqueous layer is harmful to diffusion of phenol to the center of Pd and leaded to lower activity.Finally,surface of SBA-15 and m-ZrO₂ were modified by functional ionic liquids 1-（3-trimethoxysilane）-3-methyl-imidazole chloride.The loading of ionic liquid was respectively 18.8%and 3.5%and the morphology of modified material was almost unchanged.But surface area,pore volume and pore size of samples modified were decreased,implying that ionic liquid had entered to the pore structure of the samples.