Carbon filament growth on platinum catalysts

Abstract

Steady-state and diffuse reflectance laser flash photolyses have been camed out to elucidate the mechanism of photodegradation of 1,3-diphenylisobenzofuran (DPBF) on solid surfaces of AlzO3, TiOz, and ZnO. In the absence of oxygen, the semiconductor supports TiOz and ZnO catalyze the photodegradation by accepting electrons from excited DPBF. The fluorescence of degassed DPBF on Ti02 and ZnO is quenched relative to that on alumina, thereby offering independent codmation of charge transfer. In oxygenated samples, the primary mechanism of photodegradation involves reaction with singlet oxygen. This is confirmed by the studies on the insulator surface A1203, where significant degradation is observed only in the case of air-equilibrated samples. The dependence of the rate of DPBF photodegradation on the surface coverage indicates that only the molecules that are in direct contact with the surface undergo photodegradation. The results that highlight the role of the support material in guiding the course of a photochemical reaction are described here.

Ni/SiO2 promoted growth of carbon nanofibers from chlorobenzene: Characterization of the active metal sites

“…GCN synthesis has been recorded and characterized from a catalytic decomposition of CO [1,18,19] and a diversity of aliphatic [13][14][15][16][17][20][21][22] and, to a lesser extent, aromatic [23][24][25] feedstock. Hydrogen is not an essential component in these systems but its presence has been shown to be highly beneficial in initiating decomposition of the carbon containing gas [26] and exerting additional structural control on the growing carbon [27]. While the extent of carbon growth is dependent on the composition of the reactant feed and the process conditions, the structural characteristics are largely governed by the crystallographic orientation of the exposed metal face(s).…”

Insights into carbon nanotube growth using an automated gravimetric apparatus

“…H 2 concentrations at these levels are not required for catalyst reduction, even accounting for gas flow considerations, so the benefits are typically explained by one of two mechanisms: (i) H 2 can increase yields by gasifying amorphous carbon deposits to retain catalytic activity [26,119]; however, at high H 2 concentrations and/or temperatures, this gasification process can become sufficiently aggressive to remove graphitised products and reduce CNTyields [78,81,109,123]; or (ii) H 2 stabilises the growing structure by saturating dangling bonds that would otherwise lead to closure and cessation of growth [42,97,102,119,124,125]. These may occur concurrently with H 2 effects on deposited carbon morphology [109,126,127], by catalyst structural modification [128,129], changes in surface bonding and chemistry [22], and altering carbon/metal diffusion kinetics [57,81]. Additionally, H 2 modifies the gas phase species distribution.…”

Influence of copper on the structural characteristics of carbon nanofibers produced from the cobalt-catalyzed decomposition of ethylene

“…5,23 It was, therefore, somewhat surprising to find that hydrogen appeared to have little impact on the structure of the carbon nanofibers produced on copper-cobalt particles. The carbon deposits formed during these reactions were subsequently characterized in a similar manner to that described for the material produced from the interaction of the same catalyst systems with pure ethylene.…”