New catalysts based on silicon carbide support for improvements in the sulfur recovery: new silicon carbide nanotubes as catalyst support for the trickle-bed H2S oxidation

Abstract

Nanotubos de carbeto de silício (SiC) foram preparados a partir da reação gás-sólido entre vapor de SiO e nanotubos de carbono. A fase ativa NiS 2 suportada em nanotubos de SiC apresentou maior atividade catalítica e maior capacidade de armazenamento de enxofre na reação de oxidação seletiva do H 2 S a enxofre elementar, em reator do tipo trickle-bed, que a mesma fase ativa suportada em grãos de SiC. O melhor desempenho deste catalisador foi explicado pela ocorrência do efeito de confinamento no interior dos nanotubos de SiC; ou seja, pelo aumento artificial da pressão parcial de H 2 S no interior dos nanotubos em relação à mesma pressão fora dos nanotubos, resultando assim em um aumento na taxa da oxidação, uma vez que a velocidade de reação do H 2 S é de primeira ordem. O catalisador suportado em nanotubos de SiC apresentou elevada resistência ao carregamento de enxofre devido a uma peculiar evacuação do enxofre pelo vapor de água condensado, permitindo assim uma limpeza contínua dos sítios ativos. A maior capacidade de armazenamento do enxofre sólido no suporte a base de nanotubos de SiC foi atribuído ao seu maior volume específico disponível para o armazenamento do enxofre do que o do suporte a base de grãos de SiC.Silicon carbide nanotubes were prepared via a gas-solid reaction between SiO vapor and carbon nanotubes. The NiS 2 active phase on this support displayed both a high catalytic activity and high solid sulfur storage capacity in the trickle-bed selective oxidation of H 2 S into elemental sulfur as compared to the grain-based SiC catalyst. The hypothesis of a confinement effect inside the SiC nanotubes has been put forward to explain the catalytic results. An artificial increase in the H 2 S partial pressure inside the tubes when compared to the H 2 S partial pressure outside the tubes would lead to an increase in the oxidation rate, due to the first order reaction rate toward H 2 S. The SiC nanotube supported catalyst displayed very high resistance to the sulfur loading, due to a peculiar mode of sulfur evacuation by condensed steam which allows the continuous cleaning of the active site. The high solid sulfur storage capacity was due to a much larger void volume between each SiC nanotube available for the sulfur storage, than the void volume of SiC support with a grain size morphology.

Silicon carbide nanotubes and nanotubular fibers: Synthesis, stability, structure, and classification

“…The production of SiC-NTs with external diameter~100 nm and internal diameter~50 nm by a substitution reaction in which C-NT was used as template was reported in [23,24]:…”

“…However, hollow 1D-SiC fibers with nonuniform walls, consisting not of folded close-packed layers but of polycrystalline disoriented SiC nanograins, were detected experimentally [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32]. The question arises as to whether such fibrous structures can be considered nanotubes.…”

“…Zerodimensional (0D) nanoparticles [7], 1D-nanofibers (SiC-NF), nanowires, nanowhiskers, nanorods [8][9][10][11][12][13], 2D-nanofilms and accumulations in the form of nanoflowers [12,13], and 3D-nanoporous silica and other nanomaterials having unusual properties [14] have been produced. There was a natural urge to produce silicon carbide nanotubes (SiC-NT) [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34], since a new structural state in the form of the nanotube should confer onto it new unusual characteristics of quantum nanocylinders and not nanofibers, which is of enormous interest for the growing microelectronics. A NASA project in NNI was devoted to this problem.…”

Band-gap unification of partially Si-substituted single-wall carbon nanotubes

“…[17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] The atomic structure of the resulting silicon carbide single wall nanotubes ͑SWSiCNT͒ remains very close to the original shape of the initial SWCNTs. The first theoretical investigation of the SWSiCNTs with different Si/ C ratio was done using cluster DFT 32 and PBC GTBMD approaches.…”

Síntese e caracterização de compósitos de nanotubos de carbono e nanopartículas de prata e sua aplicação como substrato SERS

“…Nanotubos são ainda bons emissores de elétrons, e seu uso tem sido proposto para o desenvolvimento de tecnologia para monitores de emissão de campo (field emission displays, FEDs) (Dimitrijevic et al, 1999;Fan et al, 1999;Keller et al, 2005;Kim et al, 2000;Monteiro et al, 2000;Talin;Dean;Jaskie, 2001).…”