Synthesis And Catalytic Performances Of Mesoporous Carbon Nitride Supported Ni-based Nanocatalysts

Carbon nitrides are fascinating materials with unique electrical conductivity,chemical stability,and mechanical stability.Mesoporous carbon nitride?MCN?materials also have a higher specific surface area,pore volume,and a rich pore structure,which are conducive to mass transfer and diffusion of reactants and products in a heterogeneous reaction.Moreover,MCN materials can also be used as catalyst carriers to improve the dispersion and stability of metal nanoparticles and thus enhance the catalytic performances.Therefore,in recent years,the design and synthesis of carbon nitrides with high specific surface area and mesoporous structure has become the research hotspot in the fields of catalysis and mesoporous materials.Boron-nitrogen hydrides,having high hydrogen content and high stability,have been considered as promising chemical hydrogen storage materials.In this thesis,we have designed and prepared a series of mesoporous carbon nitride materials supported Ni-based alloy nanocatalysts for the dehydrogenation of boron-nitrogen hydrides.The main research contents are given as follows:Highly dispersed Pd and PdNi nanoparticles?NPs?have been successfully immobilized on mesoporous carbon nitride?MCN?via a facile co-reduction approach.The resulting Pd/MCN catalyst shows an excellent catalytic performance for hydrogen release from ammonia borane aqueous solution with a turnover frequency?TOF?value of 125 min^-1at room temperature,which is the highest value for the Pd-based monometallic catalysts reported to date.The catalytic performance of the Pd NPs can be further enhanced by alloying with Ni atoms.Among all the synthesized Pd_xNi_100-x/MCN nanocomposites?NCs?with different Ni/Pd ratios,the Pd₇₄Ni₂₆/MCN catalyst exhibits the best catalytic performance with a TOF of 246.8 min^-1.The high activity of Pd/MCN and Pd₇₄Ni₂₆/MCN are largely dependent on the features of the interfacial interaction between the MCN matrix and metallic NPs,and the accessible open porous structure for freely mass transfer.The nitrogen content in MCN materials can be easily controlled by simply adjusting the pyrolysis temperatures.The Ni Pt alloy NPs supported on the MCN materials with different nitrogen contents have been synthesized via a facile co-reduction method and used as catalysts for hydrogen generation from hydrazine borane in alkaline solution at 298 K.The characterization results show that the increase in pyrolysis temperature can lead to a decrease in the nitrogen content of MCN,especially the pyridinic N.Among all the catalysts tested,the Ni₆₀Pt₄₀/MCN-800 catalyst shows the highest catalytic activity and 100%hydrogen selectivity.The TOF value of Ni₆₀Pt₄₀/MCN-800 NCs reaches up to 1111 h^-1 at 298 K,which is the highest among all the catalysts reported to date for this reaction.The research results reveal that the MCN with tunable nitrogen content plays an important role in enhancing the catalytic performaces.