Hydrogen generation from hydrolysis of sodium borohydride by silica xerogel supported cobalt catalysts: Positive roles of amine modification and calcination treatment

Abstract

Silica xerogel supported cobalt catalysts were prepared by sol-gel method to hydrogen generation from an alkaline sodium bomhydride solution. The effect of APTES (3-aminopropyl triethoxysilane) modification and calcination treatment was investigated on the structural properties and catalytic activity. The physicochemical properties of the catalysts were evaluated by using XRD (X-ray diffraction), nitrogen adsorption/desorption, TEM/EDX (Transmission electron microscopy/energy dispersive X-ray spectroscopy), XPS (X-ray photoelectron spectroscopy) and FTIR (Fourier transform infrared) analysis techniques. Only the formation of broad amorphous silica was observed from the XRD patterns. APTES modification and calcination treatment led to increasing of surface area and total pore volume values. The surface area, total pore volume and pore diameter values increased up to 752 m(2)/g, 0.693 cm(3)/g and 3.88 nm, respectively. The TEM image of the Co@X-TA-C catalyst showed that cobalt was settled as nanoparticle smaller than 4.0 nm to the structure. The average particle size of this catalyst was determined as similar to 4.5 nm. XPS analysis results demonstrated presence of metallic and oxide cobalt phases. FTIR spectra exhibited bands representing the silica structure and cobalt-silica interaction. The maximum hydrogen generation rate was determined as 100.7 mL.min(-l).g(cat)(-1) for Co@X-TA-C. Kinetic study showed that the hydrolysis of sodium borohydride with Co@X-TA-C catalyst system was a zero-order. The activation energy was found as 15.2 kImol(-1) for this catalyst.