Heterogeneous catalytic reactions of carbon dioxide

Abstract

We show that the spectral and radial distribution of the nonthermal emission of massive, M 10 14.5 M ⊙ , galaxy clusters may be approximately described by simple analytic expressions, which depend on the cluster thermal X-ray properties and on two model parameter, β core and η e . β core is the ratio of the cosmic-ray (CR) energy density (within a logarithmic CR energy interval) and the thermal energy density at the cluster core, and η e(p) is the fraction of the thermal energy generated in strong collisionless shocks, which is deposited in CR electrons (protons). Using a simple analytic model for the evolution of intra-cluster medium CRs, which are produced by accretion shocks, we find that β core ≃ η p /200, nearly independent of cluster mass and with a scatter ∆ ln β core ≃ 1 between clusters of given mass. We show that the hard X-ray (HXR) and γ-ray luminosities produced by inverse Compton scattering of CMB photons by electrons accelerated in accretion shocks (primary electrons) exceed the luminosities produced by secondary particles (generated in hadronic interactions within the cluster) by factors ≃ 500(η e /η p )(T /10keV) −1/2 and ≃ 150(η e /η p )(T /10keV) −1/2 respectively, where T is the cluster temperature. Secondary particle emission may dominate at the radio and very high energy ( 1 TeV) γ-ray bands. Our model predicts, in contrast with some earlier work, that the HXR and γ-ray emission from clusters of galaxies are extended, since the emission is dominated at these energies by primary (rather than by secondary) electrons. Our predictions are consistent with the observed nonthermal emission of the Coma cluster for η p ∼ η e ∼ 0.1. The implications of our predictions to future HXR observations (e.g. by NuStar, Simbol-X) and to (space/ground based) γ-ray observations (e.g. by Fermi, HESS, MAGIC, VERITAS) are discussed. In particular, we identify the clusters which are the best candidates for detection in γ-rays. Finally, we show that our model's results agree with results of detailed numerical calculations, and that discrepancies between the results of various numerical simulations (and between such results and our model) are due to inaccuracies in the numerical calculations.

Methanation of Carbon Dioxide Over Mesoporous Nickel–M–Alumina (M = Fe, Zr, Ni, Y, and Mg) Xerogel Catalysts: Effect of Second Metal

“…Methanation of carbon dioxide has been investigated over a number of catalysts based on VIIIB metals (for example, Ru, Rh, Ni, Co, and Fe) supported on various metal oxides (for example, SiO 2 , Al 2 O 3 , ZrO 2 , TiO 2 , and CeO 2 ) [10,11]. Among these catalysts, Ni-based catalysts have been widely employed for carbon dioxide methanation reaction due to their high catalytic activity and high selectivity for methane.…”

Methanation of carbon dioxide over mesoporous Ni–Fe–Ru–Al2O3 xerogel catalysts: Effect of ruthenium content

“…Methanation of carbon dioxide has been investigated over a number of catalysts based on VIIIB metals (for example, Ru, Rh, Ni, Co, and Fe) supported on various metal oxides (for example, SiO 2 , Al 2 O 3 , ZrO 2 , TiO 2 , and CeO 2 ) [10][11][12]. Among these catalysts, Nibased catalysts have been widely employed for carbon dioxide methanation reaction due to their high catalytic activity and high selectivity for methane.…”

Segregation of Pt and Re During CO2 Reforming of CH4

“…Commercialization of dry reforming has been limited due to equilibrium considerations and its highly endothermic nature, which require temperatures near 800°C for acceptable conversions [6,7]. At such temperatures, the catalyst deactivates due to carbon deposition.…”