Mechanism Of Controllable Synthesis Of Ni/HBEA With Hierarchical Core-shell Structure And Its Application

Nickel based catalyst has been widely applied to various industrial processes due to its low price and high activity.A kind of core/shell Ni/HBEA catalyst has been hydrothermally synthesized through adding hierarchical HBEA solid into NH₃·H₂O/NH₄Cl buffer solution.The prepared catalyst preserves most of the crystal morphology of HBEA,while most of the nickel particles are dispersed around the surface of the zeolite,and the rest are encapsulated into the mesopores of the zeolite.（41 wt%,5.9 ± 0.7 nm）.With respect to investigation of the mechanism of hydrothermally synthesized Ni/HBEA catalyst,the formation of the precursor nickel phyllosilicate and a two-step process of "dissolution-recrystallization" are confirmed with in situ IR,XRD,TEM,SEM,ICP-AES,TPR,and solid NMR as a function of synthesis time from 20 to 120 min.Firstly it is under the dissolution of silicon without the change of aluminum element,and after the dissolved Si（IV）concentrations excels the solubility of the nickel phyllosilicate nanosheets,the further growth of the multilayered nanosheets of nickel phyllosilicate starts.It should be noted that the precursor,nickel phyllosilicate can not been formed with sole NH₄Cl as the precipitate and is also changeable between 1:1 nickel phyllosilicate and 1:2 nickel phyllosilicate,due to the competition between kinetically-favored species and thermodynamically-controlled species in terms of the different hydrothermal condition.The developed core/shell hierarchical bifunctional Ni/HBEA catalyst leads to a high activity on a model reaction of stearic acid hydrodeoxygenation with a promising rate of 54 g-g-1·h-1.Based on the research above,a kind of simple,green hydrothermal method has also been developed with water as the sole solvent.In this new catalyst prepared method,only the zeolite and the weak-acid-weak-base salt are used without adding any precipitate.As a result,the filtrate will be relatively pure,so that it can be reused,which introduce a new idea for the solution of discharge of waste water.In addition,the nickel loading of the catalyst can be controlled according to the concentration of nickel solution,while the distribution of particles is limited according to the formation of nickel phyllosilicate.According to its two-step preparation principle,nickel salts with weaker base and the carrier which can be partly dissolved in water with suitable rate are preferred.And the high-nickel loading catalysts are of higher activity and selectivity,comparing with those prepared through traditional methods,such as deposition-precipitation or impregnation in hydrodeoxygenation and hydrogenation reaction.