Study On Supported Cataltsts And Properties Of Surface Structure Controlled By Hydrotalcite As Precursor

The layered double hydroxide is a homogeneous,basic mixed metal hydroxide having a layered structure,and has characteristics such as acid-base adjustability,cation adjustability,adsorption capacity,thermal stability,and ion exchange.It is considered to be an advanced nanostructured catalyst carrier that controls the position of catalytically active metal species.Among them,LDH and its MMO have been used as environmentally friendly and recyclable heterogeneous solid base catalysts in place of conventional homogeneous base catalysts for several types of organic reactions.On the one hand,under certain temperature calcination,LDHs can be converted into mixed metal oxides(MMO)with large surface area and a large amount of Lewis base dispersion.By adjusting the cations and controlling the uniform dispersion of the cations,heat treatment can obtain a variety of composite metal oxidation.Things.On the other hand,LDHs are a kind of porous materials,which are easy to fix metal nanoparticles.The rich hydroxyl groups on the surface can interact with metal particles.The carrier effect and ligand effect play a significant role in the activity of the catalyst.Significant effect in the reaction.(1)Calcium cobalt iron hydrotalcite with different metal elements was synthesized in one step by coprecipitation method.In order to further construct more oxygen vacancies,the proportion of metal cations in the laminate was adjusted during the synthesis.A series of ruthenium-based eatalysts were prepared on the basis of calcination and high temperature reduction.By comparing the specific surface of the different catalysts and the analysis of the electronic states of the individual elements of the composite metal oxide.The results show that with the increase of Co2+ content,the relative content of oxygen defects on the surface of the sample gradually decreases.In guaiacol(GUA)hydrodeoxygenation reaction,after selecting the optimal catalyst,the effects of different reaction eonditions on the eatalytic performance were investigated.The results indicated that phenol was formed by demethoxylation and then hydrogenated to form cyclohexanol.The presence of the catalyst Ca2+provides an alkali source,the presence of which inhibits the non-selective C-O dissociation of the Ru catalyst,and also facilitates the demethylation step by stabilizing the produced phenol.In addition,the sample indicates that the presence of an oxidized cerium species promotes the progress of the hydrogenation reaction.(2)Presently,aerobic oxidation of carbonyl-containing compounds into high value-added carboxylic acids in the absence of any homogeneous bases has received increasing attention in terms of the attracting character of promising and sustainable process.In this work,a new hybrid composite of hydroxyapatite and Ca-Al layered double hydroxide(HAP-LDH)was assemblied via an in-situ growth route,by which large quantities of small needle-like HAP crystals in situ grew over the lateral surface of CaAI-LDH,and applied to immobilize Au nanoparticles for base-free aerobic oxidation of glucose in water to produce gluconic acid using molecular oxygen.A combination characterizations revealed that the activity of supported Au catalysts was strongly related to the composition of supports,and the hybrid HAP-LDH supported one with the Au loading amount of 0.2 wt%delivered a high gluconic acid yield of>98%under the optimal reaction conditions,along with a quite high turnover frequency value of～20225 h-1.High catalytic efficiency of the as-formed Au/HAP-LDH was mainly assigned to a cooperation between favarable surface Au species(Au0/Auδ+)and abundant basic sites.Furthermore,the present catalyst also presented good structural stability,because of novel hybrid three-dimensional nano/microstructure of HAP-LDH composite support facilitating the stabilization of active Au species and components of the support.The present synthesis strategy of employing hybrid composite support provides a new way to design stable and highly efficient supported metal nanocatalysts for a variety of advanced heterogenous catalytic processes.