Study Of Synthesis, Characterization And Property On MPV Reduction Of α, β-unsaturated Aldehydes With Supported ZrOx Catalysts

α,β-Unsaturated alcohols are industrial interest because many ofthem are important intermediates in the production of pharmaceuticals,agrochemicals, and fragrances. They may be produced by chemoselectivereduction of unsaturated ketones and aldehydes. Because thehydrogenation of the C=C bond is thermodynamically more favored, theselective hydrogenation of the C=O bond become important. Meerwein-Ponndorf-Verley （MPV） reaction is an important route of synthesize ofα,β-unsaturated alcohols. In mild conditions, using secondary alcohols ashydrogen donors, MPV reaction provides a highly selective reduction ofthe C=O functional group. Zirconia catalysts are increasingly used inMPV reaction catalysis due to its high activity, water resistance, poisonresistance and reusable.Doped Zr-MCM-41 were synthesized by sol-gel method, supportedZrOx/MCM-41, ZrOx/Al-MCM-41, ZrOx/zeolite, ZrOx/SiO₂, ZrOx/MgO, ZrOx/Al₂O₃ and ZrOx/C were synthesized by impregnationmethod. These samples were investigated in MPV reaction of benzylaldehyde cinnamalhyde with 2-propanol as reductant, characterisatedwith XRD, N₂ sorption, TG-DTA, IR, UV, NH₃-TPD. Water resistance,poison resistance and regeneration was tested to ZrOx/MCM-41,ZrOx/Al-MCM-41 and ZrOx/C.In the supported ZrOx/MCM-41, activity site of ZrOx is on thecatalyst’s surface. In doped Zr-MCM-41, ZrOx is in the wall. Sosupported ZrOx/MCM-41 has higher activity in these catalysts. TheSi-O-Zr-OH on the surface of ZrOx/MCM-41 has higher activity thanZr-OH. In the Zr loading range of 2.5～20%, the content of Si-O-Zr-OHalmost hasn’t changed, so the activity of the catalysts were slightlyaffected by Zr content. When the content is up to 25%, the framework hasbe destroyed, and the activity was sharply decreased.The activity of catalysts was affected by the framework andacid/base of support. The catalyst has high activity which has neutralsupport, large surface area, large pore size and uniform pore sizedistribution.In ZrOx/C, there isn’t interaction between the active carbon and theZrOx active component. The activity of catalyst was only affected by theexposure area of the ZrOx/C. In the Zr loading range under 5%, ZrOxwas single-layered loading on the surface of the support. Because of the hydrophobic of the active carbon, when the Zr content is above 5%, ZrOxwill be gathered, to exceeding 15%, the nanometer ZrO₂ was appeared,and the surface of the catalyst was improved. At the Zr content of 2.5～5%,the activity of ZrOx/C was improved, at the Zr content of 5～15%, theactivity of ZrOx/C was steady, at the Zr content of 15～25%, the activityof ZrOx/C was improved smoothly. Increase of calcined temperatureleads to sharp decrease of the activity of the catalyst, due to the decreaseof the Zr-OH and support.ZrOx/C、ZrOx/MCM-41 and ZrOx/Al-MCM-41 have good waterresistance. They retained almost 57%, 50% and 39% of their activity inthe presence of 1.5% water. Because of hydrophilic and hydrophobicsupports, these catalysts have different water resistance. Water film canbe easy formed on the surface of hydrophilic supports, and the diffuse ofreactants to the active sites will become difficult, so the activity of thecatalysts decreased. The activity of these catalysts decreased in thepresence of acid, and ZrOx/C has the best acid resistance. The activity ofZrOx/MCM-41 in the MPV reduction of cinnamalhyde improved in thepresence of triethylamine （（CH₃CH₂）₃N）, and the highest conversion ofcinnamalhyde is 98.3%. The cinnamalhyde will be covert easily tocinnamic acid, the acid is the poison of the catalyst. Triethylamine willcombine with cinnamic acid when it was added, and the active site wasslight affected by the complex of triethylamine and cinnamic acid, so the activity of ZrOx/MCM-41 was improved interestingly. In the reaction ofother substrates over other catalysts, triethylamine decreased theconversion. Active component have no leaking in ZrOx/MCM-41 andZrOx/Al-MCM-41, and a little leaking in ZrOx/C. These three catalystshave good regeneration, and the order is: ZrOx/MCM-41＞ZrOx/Al-MCM-41＞ZrOx/C.There is a high selection in MPV reduction of benzyl aldehyde, andthe byproducts are aethers. In the MPV reduction of cinnamalhyde, thereis no byproduct can be tested.