Design Synthesis And Catalytic Performance Of Multi-metal Oxide Based Composites

Metal oxides have shown broad application prospects in oxidation,acid-base catalysis,and other fields due to their unique structural characteristics.In the past few decades,the development and synthesis of metal oxide-based composite nanomaterials have gradually become a research hotspot,and the morphology,composition,and performance regulation of composite materials have been achieved.However,there are new challenges in how to control its selectivity while improving catalytic activity.The main goal of this thesis is to develop new metal oxide based composite nanomaterials,and further explore the effects of structural composition and doping of the composite materials on the catalytic activity and selectivity of specific catalytic reactions.The main achievements are as follows:1.The Co1-xCexO2-δ multi-shelled nanospheres with various Ce/Co ratios for low temperature CO oxidation were fabricated by using the bimetallic coordination polymer as self-sacrificial template.The obtained Co0.9Ce0.1O2-δ catalyst existed superior CO oxidation performance,which reached 100%conversion at 80℃.After five-cycle tests,the conversion could also be maintained at approximately 100%with almost no activity loss.Furthermore,the effects of CeO2 component on catalytic performance have been investigated by various advanced physicochemical characterizations.It indicated that the addition of cerium can significantly increase the surface area,so as to enrich the oxygen vacancies and provide a higher degree of accessible active sites.This work proposed an alternative approach to construct multi-shelled nanospheres composites.2.We reported an advanced catalyst fabricated by coupling Cu and Fe4N to form an entirety.The catalyst was first synthesized via a hydrothermal route to obtain a Cu-Fe mixed metal oxide precursor,which was subsequently obtained through ammoniation.The catalyst possessed remarkably enhanced capability to convert CO2 into formic acid without alkaline additives.Specifically,a catalytic mass specific activity of 0.621 mmolFA g-1 h-1 was achieved over the Cu-Fe4N catalyst within 6 h at 140℃.For comparison,CuFeO2 exhibited high selectivity to methanol,but the activity was low.Further experimental and computational investigations verified that the Cu-Fe4N interface was highly polarized,contributing to abundant Cu2+ species.It was significant for performance enhancement by generating high-active Cu-CuO-FeCO3 three-phase boundary through an in situ conversation process during catalysis,whereby Cu played a crucial role in H2 activation,and CuO and FeCO3 cooperatively response to CO2 activation and selective conversion.3.We have synthesized a series of Pd/ZnCo2O4 supported catalytic materials with low noble metal loading and high activity by impregnation method for low-temperature CO oxidation.The results showed that the catalytic material exhibited excellent CO oxidation activity(complete conversion temperature of 90℃)and high catalytic stability(five cycles)at a Pd loading of 0.2%.A series of characterization results indicated that this excellent catalytic performance stemed from the interaction between metal Pd and carrier ZnCo2O4.Pd provided more available active sites,while ZnCo2O4 as a carrier could better stabilize Pd nanoparticles.The content of Pd2+species in Pd/ZnCo2O4 increased with the enhancement of the electronic interaction between Pd and ZnCo2O4,thereby improving the catalytic activity of CO oxidation.In addition,the low loading of Pd was crucial for reducing the cost of precious metal catalysts and improving their practicality in industrial applications.4.We prepared Ni3N/SiO2 and Na-Ni3N/SiO2 catalysts using simple heat treatment methods and impregnation methods to improve the activity and control the selectivity of the reaction during CO2 hydrogenation.The effects of Na additives on Ni3N/SiO2 catalysts were studied through various characterizations in terms of reaction rate,selectivity,and reaction mechanism.The synergistic effects between various metals were studied.The results showed that the deposition of Na could significantly increase the adsorption rate of CO2 on the catalyst and significantly inhibit the methanation of CO to CH4,thereby effectively controlling the selectivity in the process of CO2 hydrogenation to CO.