MOFs-Derived Transition Metal Oxides/Carbon Materials For CO Activation And Conversion

Metal-organic frameworks(MOFs)are a class of porous materials constructed by coordination of metal ions/clusters and organic ligands.Due to their excellent physical and chemical properties,MOFs have recently attracted increasing research interest in various fields.However,due to the drawbacks of low catalytic active sites,insufficient electronic conductivity,and poor chemical stability of most pristine MOFs,converting MOFs into metal compounds,carbonaceous materials,or their composites would be promising to address these issues for catalysis applications.This thesis aims to develop novel and highly efficient MOFs-based catalysts for CO activation and conversions such as CO oxidation and CO hydrogenation to aromatics,by employing MOFs with specific structures as sacrificing templates.The structure-performance relationships and the reaction mechanism over the MOF-based catalysts are also explored.The main contents of this thesis and the obtained main experimental results are as follows:The engineering of highly active,stable,and inexpensive catalysts for CO oxidation reaction through the modulations of morphology and structure is desirable but remains a great challenge.We report the rational design of novel hollow-Co3O4@Co3O4@SiO2 multi-yolk-double-shell nanoreactors by using a two-step annealing recipe with the core-shelled ZIF-67@SiO2 as precursor.The unique structures of the multiyolk-double-shell and hollow interior of Co3O4 endow the materials with promising properties of porous structures,efficient oxygen delivery capacity,and more oxygen vacancies,which are beneficial for CO oxidation.Consequently,the H-Co3O4@Co3O4@SiO2(35)-250 nanoreactor exhibits outstanding catalytic performance,achieving complete CO conversion at 100?,which is far exceeding that of hollow Co3O4 NPs derived from pure ZIF-67 and also solid Co3O4@SiO2(35)-250 with a complete conversion of CO at 190 and 230?,respectively,and even outperforms most of the reported Co3O4-based catalysts.Moreover,H-Co3O4@Co3O4@SiO2(35)-250 can continuously work for 28 h without any deactivation and maintain 93%CO conversion within 34 h at 100?We unprecedentedly explore a facile "efect mediated outward contraction" strategy to fabricate three dimensions(3D)hollow-out ZnZrO@C(HO-ZnZrO@C)catalysts by carbonizing local defect-engineered multivariate UiO-66(ZnZr)(MTV-UiO-66(ZnZr)).In this way,the obtained HO-ZnZrO@C materials with the unique architecture are able to provide the advantages of abundant surface oxygen vacancies,enhanced density of exposed active sites,open and successive channels,and structural robustness.Strikingly,this efficient strategy is versatile and could be successfully extended to the fabrication of other similar structures,e.g.,HO-CoZrO@C,HO-NiZrO@C,and HO-CuZrO@CThe HO-ZnZrO@C and hierarchical H-ZSM-5 tandem catalyst with powder mixing mode not only affords the selectivity of aromatics up to 73.1%,but also suppresses the CH4 selectivity down to 3.4%at the CO conversion of 35.2%.Particularly,we achieve the record-high space-time yield of 0.302 g goxide-1 h-1 for methanol-intermediated COx hydrogenation to aromatics over tandem catalyst systems with high catalytic stability.The 2,6-di-tert-butyl-pyridine adsorption FTIR results indicate that the powder mixing mode between HO-ZnZrO@C and H-ZSM-5 decreases the number of external Br(?)nsted acid sites on H-ZSM-5,which is beneficial to selective hydrogenation of intermediates into aromatics Our strategy might open up a new avenue for the rational design of highly open hierarchical nanostructures with targeted functionalities for various advanced applications.