Preparation Of Supported M@MIL-n Catalysts For Hydrolytic Dehydrogenation Of Ammonia Borane

Metal-organic frameworks (MOFs) are porous crystalline hybrid organic-inorganic materials constructed by metal ions coordinated to multi-dentate organic ligands. MOFs represent a new class of hybrid functional materials due to their large specific surface area and porosity as well as tunable structure and properties. So, in the application of many catalyst, MOFs as the support for metal nanoparticles is widely used in hydrogen energy. Based on the structural features and chemical properties of MOFs, a series of highly active MIL-n (n=53,101) supported metal catalysts(M@MIL-n) were designed and prepared, and they showed excellent catalytic activity in ammonia borane hydrolysis to generate hydrogen gas. The main research contents are as follow:1. Ultrafine Ru nanoparticles are successfully deposited on MIL-53(Cr) and MIL-53(A1) by using a simple liquid impregnation strategy and then investigated the catalysts by XRD, TEM, EDX, ICP-AES, XPS and BET. Their catalytic activities had been examined in ammonia borane hydrolysis to generate hydrogen gas. The results show that the as-synthesized 2.65 wt% Ru@MIL-53(Cr) and 2.59 wt% Ru@MIL-53(Al) exhibit the highly catalytic activity, owing to the uniform distribution of Ru nanoparticles and bi-functional effects between Ru nanoparticles and the host of MIL-53. The turn over frequency (TOF) values of the 2.65 wt% Ru@MIL-53(Cr) and 2.59 wt% Ru@MIL-53(Al) catalysts are 260.8 and 266.9 mol H2 min-1(mol Ru)-1 and the activation energies (Ea) are determined to be 28.9 and 33.7 kJ mol-1, respectively. Moreover, the two catalysts exhibit satisfying durable stability after five cycles for the hydrolytic dehydrogenation of ammonia borane.2. Bimetallic PdNi nanoparticles with different molar ratio supported on MIL-101 have been successfully synthesized by a simple liquid impregnation method. And a series of characterization methods were used to determine the structure, composition, morphology and load behavior. Their catalytic activities were tested in the hydrogen generation from aqueous solution of ammonia borane at room temperature. The results show that the as-synthesized PdioNi6@MIL-101 catalyst exhibits the highest catalytic activity, with a total turn over frequency (TOF) value of 83.1 mol H2 min-1 (mol Pd)-1, and the activation energy (Ea) is determined to be 31.7 kJ mol-1. The excellent catalytic activity has been successfully achieved thanks to the strong bimetallic synergistic effects from PdNi nanoparticals of the composites, uniform distribution of nanoparticles as well as bifunctional effects between PdNi nanoparticles and the host of MIL-101. In particular, this catalyst shows satisfying durable stability after five cycles of reaction, retaining 85% of its initial catalytic activity.3. The catalysts containing Ru, CuCo and trimetallic RuCuCo nanoparticles were successfully synthesized by in-situ reduction of Ru, Cu and Co salts into metal-organic framework MIL-101 via a simple liquid impregnation method, and then characterized the structure, size, composition and specific area of the catalysts with different metal nanoparticles loading by a series of characterization methods. The as-synthesized RuCuCo@MIL-101 exhibits a higher catalytic activity than those of monometallic Ru and bimetallic CuCo counterparts loadings, owing to the strong trimetallic RuCuCo synergistic effects, uniform distribution of alloy particles as well as bi-functional effects between nanoparticles and the host in the hydrogen generation from aqueous solution of ammonia borane, with the turn over frequency (TOF) value of 241.2 mol H2 min-1 (mol Ru)-1 and the activation energy (Ea) is determined to be 48 kJ mol-1. Moreover, the catalyst showed excellent stability after cyclic testing.