New Ni Nanowire / Sio <sub> 2 </ Sub> Composite Airgel Preparation, Structure And Performance

Ni nanowires/SiO₂ composite aerogels have well kept the nano network structure and high BET surface of silica aerogel.Ni nanowires are well dispersed in porous SiO₂ matrix,form a large number of surface adsorption sites of hydrogen and lead to a great potential application in catalytic hydrogenation and dehydrogenation reaction.Ni/SiO₂ composite aerogels have been prepared by sol-gel process combining with supercritical drying using nickel nitrate as nickel source,TEOS as carrier source and ethylene glycol as solvent and reducing agent.The impact of process parameters on their density and specific surface areas as well as gelation time have been studied.TEM,XRD,IR,adsorption/desorption of nitrogen,TPR,H₂-TPD are used to characterize the composite aerogel specimens.Ni content of composite aerogels is 0-23%.Most of Ni²⁺ has been reduced to Ni⁰ by ethylene glycol.And the other Ni²⁺ is hard to be reduced for cohering with the surport.TEM images show a homogenous and uniform distribution of Ni nano-wires in the porous SiO₂ matrix.The nanowires have fcc structure,less than 100nm long,their diameters 1-3nm.With the load of metal increase,the number and size of nanowires incease,catalytic activity also increase as more active sites Ni⁰ exist.After heat treatment at 530℃,the nano network structure of composite aerogels haven't changed significantly,nanowires haven't shown obviously aggregation and growth.Specific surface area decreases slightly under 530℃,but still considerable.The impacts of various additives on the structrue and properties of Ni/SiO₂ composite aerogels have been studied.The number of surface adsorption sites increase greatly on CeO₂-Ni-SiO₂ and Mg-Ni-SiO₂ aerogels because Ce³⁺ and Mg²⁺ have dispersed nickel.H₂ could be more easily desorbed on Zr-Ni-SiO₂ aerogel.TiO₂-Ni-SiO₂ aerogels have a new active site of anatase TiO₂ generated.CaCO₃-Ni-SiO₂ aerogels also have another adsorption site.