Silica gel

About: Silica gel is a research topic. Over the lifetime, 22313 publications have been published within this topic receiving 325516 citations. The topic is also known as: Amorphous silica & Precipitated amorphous silica.

Preparation of Ni/SiO2 catalyst with high thermal stability for CO2-reforming of CH4

Abstract: Silica-supported nickel (Ni/SiO 2 ) catalysts were prepared by homogeneous precipitation of nickel hydroxide in a wet silica gel derived from a sol–gel process (HPG). Their microstructures and their catalytic performance for the CO 2 -reforming of CH 4 were investigated in comparison with those of Ni/SiO 2 prepared by a conventional incipient wet impregnation process (IMP). The HPG process consists of two successive steps: gelation of silica in the presence of nickel nitrate and urea at 20 °C, followed by aging at higher temperature, typically at 80 °C, to induce thermal decomposition of the urea. The nickel metal surface area of the HPG catalysts was larger than that of IMP catalysts at each calcination temperature. Nickel species in HPG catalysts are expected to be entrapped in the network of silica with high dispersion, while those in IMP catalysts are expected to aggregate on the surface of silica. The characteristic structure in HPG catalysts is considered to be formed through concurrence of dissolution–reprecipitation of silica and entrapment of nickel species into the network. Such processes are promoted in a basic condition led by NH 3 formation during thermal decomposition of urea at 80 °C. The amount of carbon deposited and the catalytic deactivation degree in HPG catalysts were smaller than those in IMP catalysts. Thermal stability of HPG catalysts was much higher than that of IMP catalysts and catalytic activities of the former were higher than those of the latter. This originates in the highly-dispersed nickel metal particles in the rigid network of silica for HPG catalysts.

Diborane Release from LiBH4/Silica-Gel Mixtures and the Effect of Additives

Abstract: LiBH4 that has been ball-milled with different additives and subsequently mixed with mesoporous silica-gel has been investigated using thermal desorption spectroscopy and thermogravimetry. Mixtures of LiBH4 and mesoporous silica-gel (composition 50:50 wt %) release hydrogen at ∼260 °C. Samples, where LiBH4 was ball-milled prior to mixing with silica-gel with 5 mol % PdCl2, NiCl2, LaCl3 or TiCl3, have similar decomposition temperatures. Mass spectrometry data of the emitted gas streams show that almost all hydrogen desorption events are accompanied by the evolution of gaseous diborane, B2H6. The relative diborane concentration above 350 °C is considerably lowered by LaCl3 and TiCl3, whereas the other additives investigated have little influence on the amount of released diborane.

The Colloid chemistry of silica : developed from a symposium sponsored by the Division of Colloid and Surface Chemistry at the 200th National Meeting of the American Chemical Society, Washington, DC, August 26-31, 1990

Abstract: Colloid chemistry of silica - an overview, Horacio E. Bergna. Part 1 Preparation of sols: silica nucleation, polymerization and growth - preparation of monodispersed sols, Akitoshi Yoshida the formation and interfacial structure of silica sols, John D.F. Ramsay et al synthesis and characterization of colloidal model particles made from organoalkoxysilanes, A. van Blaaderen and A. Vrij synthesis of nanometer-sized silica by controlled hydrolysis in reverse micellar systems, F.J. Arriagada and K. Osseo-Asare formation of silica gels composed of micrometer-sized particles by the sol-gel method, Hiromitsu Kozuka and Sumio Sakka. Part 2 Stability of sols: stability of aqueous silica sols, Thomas W. Healy. Part 3 Surface chemistry of silica: the surface structure of amorphous and crystalline porous silicas - status and prospects, K.K. Unger infrared study of chemical and H-D exchange probes for silica surfaces, B.A. Morrow and A.J. McFarlan Fourier transform infrared and Raman spectroscopic study of silica surfaces, A. Burnear et al surveying the silica gel surface with excited states, R. Krasnansky and J.K. Thomas surface chemistry and surface energy of silicas, Alain M. Vidal and Eugene Papirer variable-temperature diffuse reflectance Fourier transform infrared spectroscopic studies of amine desorption from a siliceous surface, Dondald E. Leyden and Kristina G. Proctor multinuclear NMR spectroscopy studies of silica surfaces, Gary E. Maciel et al. Part 4 Particle size and characterization techniques: new separation methods for characterizing the size of silica sols, J.J. Kirkland characterization of colloidal and particulate silica by field-flow fractionation, J. Calvin Giddings et al interpretation of the differences between the pore size distributions of silica measured by mercury intrusion and nitrogen adsorption, A.R. Minihan et al. Part 5 Sol-gel technology. Part 6 Silica gels and powders. Part 7 Silica coatings. Part 8 Uses of colloidal silicas. Part 9 Research in Russia. (Part contents)

Analysis of bacterial menaquinone mixtures by reverse-phase high-performance liquid chromatography.

Abstract: Publisher Summary This chapter describes a reverse- phase high-performance liquid chromatography (HPLC) method for isolation and identification of bacterial menaquinone mixtures. The menaquinones are referred to as MK- n , where n is the number of isoprene units in the side chain. If the isoprenoid side chains are partially saturated, they are referred to as MK- n (H m ), where m is the number of hydrogen atoms which saturate the side chain. Identification by HPLC is based on the elution time, and use of at least one standard menaquinone is necessary. A change in eluent composition can also affect elution time. For the preparation of sample for HPLC determination, menaquinone mixture is extracted from 20 mg of lyophilized cells with 10 ml of chloroform-methanol (2:1, v/v). Although the content of menaquinone in bacteria is variable, 20 mg of lyophilized cells is enough for HPLC determination in many cases. The extract is filtered with a filter paper and dried in vacuo . The residue is dissolved in a small quantity of acetone and purified quinones by thin-layer chromatography (TLC), using Merck kieselgel 60 GF 254 or an F 254 plate and a developing mixture of petroleum ether (bp 60–80°)-diethyl ether (85 : 15, v/v). Vitamin K 1 is used as a standard which has an R f of about 0.7. The menaquinone mixture is eluted from the silica gel with acetone. The solution is filtered through a 0.45- μ m pore filter and stored at –20°.