Syntheses Of Metal Supported Zeolites And SAPO-34 Zeolites With High Catalytic Performance

Energy is an essential material basis for human survival and development,and the development and utilization of energy has enormously boosted the prosperity of human society.The constant growth of world economy is causing a dramatic increase of the world's energy consumption.While this rising energy demand is presently met by the increasing use of fossil fuels,these resources are dwindling at alarming rates.Hydrogen is one of the most promising candidates to replace classic fuel sources used nowadays,and formic acid?FA?is considered as one of the most promising materials for hydrogen storage.The development of efficient catalysts for FA decomposition remains the main hurdle for practical applications of formic acid.Supported Pd-containing NPs are the most active heterogeneous catalysts for the dehydrogenation of formic acid.Zeolites have drawn growing attention as ideal supports for con?nement synthesis of metal NPs due to their well-de?ned channels,tunable acidity and basicity,as well as high thermal and chemical stability.Therefore,Pd-containing clusters encapsulated within zeolite matrix would be a potential catalyst with high performance of FA decomposition.The constant growth of world economy is also aggravating the consumption of light olefins,which are mainly from petroleum cracking.Due to the worldwide petroleum resources shortage,the great increase of the price of crude oil,and the availability of huge quantities of methanol,the methanol-to-ole?n?MTO?technology,regarded as an alternative process for the production of light ole?ns from nonpetroleum sources,has received considerable significant academic and industrial attention.The SAPO-34 catalyst with zeotype CHA,which is considered as one of the most excellent MTO catalysts,gives a very high selectivity?>80%?to light olefins with 100% conversion of methanol.However,the main problem associated with theSAPO-34 catalyst is the rapid deactivation during methanol conversion.Previous studies demonstrated that nano-sized and hierarchical SAPO-34 zeolites can remarkably prolong the catalytic lifetime and improve the selectivity of light olefins.In this doctoral thesis,we aim to synthesize metal supported zeolites and SAPO-34 zeolites with high catalytic performance.We have synthesized subnanometric Pd clusters encapsulated within Silicalite-1?MFI?zeolite under direct hydrothermal conditions,which show an excellent activity and highly efficient H2 generation.In addition,the as-synthesized catalysts possess superior thermal stabilities as well as excellent recycling stabilities.Furthermore,we have also synthesized subnanometric Pd-Ni?OH?₂ bimetallic clusters encapsulated within nanosized purely siliceous S-1 zeolite under the simliar condition.The hybrid bimetallic catalysts exhibit excellent shape-selective catalytic performance and highly efficient CO-free generation of H2 via complete FA decomposition without any additives.Significantly,the 0.8Pd0.2Ni?OH?₂@S-1 catalyst affords the highest initial and total TOF values up to 5803 h-1 at 60 °C,which are the highest values ever reported under the similar conditions.In addition,we have synthesized nano-sized hierarchical SAPO-34 zeolite catalysts by the seed-assisted method,which show superior performance in the methanol-to-ole?n?MTO?reaction.1.Well-dispersed and ultrasmall Pd clusters encapsulated within the intersectional channels of nanosized Silicalite-1?MFI?zeolite have been firstly prepared using [Pd?NH2CH2CH2NH2?2]Cl2 as precursor under direct hydrothermal conditions.The as-prepared catalysts show an excellent activity and highly efficientH2 generation,without generating CO,toward the complete decomposition of FA in aFA-SF system under mild conditions.High-resolution scanning transmission electronmicroscopy and X-ray absorption fine structure studies indicate that the subnanometric Pd clusters are encapsulated within the intersectional channels of MFI,and the Pd clusters in adjacent channels visually aggregate,forming nanoparticles?NPs?of ?1.8 nm.Notably,the Pd/S-1-in-K catalystwith incorporated basicity affords the highest TOF values,reaching up to 3027 h-1 at 50 °C,due to the further reduced Pd cluster size and basic sites introduced in the zeolites.In addition,the as-synthesized catalysts possess superior thermal stabilities as well as excellent recycling stabilities during FA decomposition due to the good con?nement of Pd clusters within the zeolite matrix.2.A facile and one-pot synthesis strategy has been developed to prepare subnanometric Pd-Ni?OH?₂ bimetallic clusters encapsulated within nanosized purely siliceous Silicalite-1 zeolite using metallic ethylenediamine complexes as precursors under direct hydrothermal conditions.X-ray photoelectron spectroscopy and X-ray absorption fine structure studies indicate that the subnano Pd-Ni?OH?₂ clusters are encapsulated within the intersectional channels of MFI zeolite.The hybrid bimetallic nanocatalysts exhibit excellent shape-selective catalytic performance and highly efficient CO-free generation of H2 via complete FA decomposition without any additives under mild conditions.Significantly,the 0.8Pd0.2Ni?OH?₂@S-1catalyst affords the highest initial TOF values up to 5803 h-1at 60 °C,which are the highest values ever reported under the similar conditions.DFT calculations demonstrates that the synergistic effect between ultrasmall Pd and transition metal hydroxides clusters can considerably decrease the activation barrier for FA decomposition,thereby enhancing catalytic activity.The superior catalytic performance,excellent thermal and recycling stabilities of these hybrid bimetal catalysts not only create a new prospect for their practical application in FA dehydrogenation as a viable and effective chemical hydrogen storage medium forfuel cells,but also raise more possibilities for their use in other important high-performance catalytic reactions.3.A facile and cost-effective strategy has been developed to synthesize nano-sized SAPO-34 zeolite catalysts with intracrystalline meso-macroporosity as well as high crystallinity and product yield via the seed-assisted method using triethylamine as the sole template.Signi?cantly,compared to conventional micron-sized microporous SAPO-34 zeolites,the nano-sized hierarchical SAPO-34 zeolites show superior performance in the methanol-to-ole?n?MTO?reaction with a4-fold prolonged catalytic lifetime and remarkably improved selectivity for ethylene and propylene reaching up to 85%,which is among the highest catalytic performances in the MTO reaction ever reported under similar conditions.High-resolution transmission electron microscopy studies indicate that the seed crystals are continually dissolved into the gel phase introducing more void spaces during the process of crystallization and the crystal growth further proceeds on the internal and outside surface.