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The deactivation pattern of a "model" Ni/MgO catalyst in the pre-reforming of n-hexane with steam (T, 450 °C; P, 5-15 bar) is reviewed. The influence of the steam-to-carbon ratio (S/C, 1.5-3.5) on the rate of catalyst fouling by coking is ascertained. Catalyst fouling leads to an exponential decay in activity, denoting 1st-order dependence of the coking process on active sites availability. Hydrogen hinders the coking process, though slight activity decay is due to sintering of the active Ni phase. Deactivation by thiophene causes a sharp, almost linear, drop to nearly zero activity within only 6 h; this deactivation is likely due to dissociative adsorption of thiophene with subsequent strong, irreversible chemical adsorption of S-atoms on active Ni sites, i.e., irreversible poisoning. Modeling of activity decay curves (α, at/a0) by proper kinetic equations allows assessing the effects of temperature, pressure, S/C, H2 and thiophene feed on the deactivation pattern of the model Ni/MgO catalyst by coking, sintering, and poisoning phenomena. [ABSTRACT FROM AUTHOR]

Abstract: A class of MnCeO x catalysts has been synthesized via the new redox-precipitation route in alternative to the conventional co-precipitation technique. The effects of preparation method, composition and calcination temperature on catalyst texture, dispersion and reduction pattern properties have been addressed. Redox-precipitated systems exhibit high surface area (SA, 120–170m2/g), large pore volume (PV, 0.4–0.5cm3/g) and a “narrow” pore size distribution (PSD) in a wide range of the Mn/Ce ratio (1/3–3/1). A quasi-molecular dispersion markedly improves oxide-support interactions and reducibility of the active phase. Redox-precipitated systems show a superior performance in the catalytic wet oxidation of phenol with oxygen (CWAO) at 373K in terms of substrate and total organic carbon (TOC) elimination and mineralization (i.e., CO2 formation) selectivity. Carbon mass-balance from TG-DSC data of used catalysts and CO2 selectivity values signal that the CWAO of phenol proceeds via a L–H reaction path, the oxidation of C-containing species being the rate limiting step (r.l.s.). Then, an optimum average pore diameter (APD, 10–15nm) enhances the rate of the adsorption step, while a straight relation between CO2 selectivity and reducibility prove that dispersion and redox properties of the active phase control the mineralization activity of the MnCeO x system. [Copyright &y& Elsevier]

Abstract: A new synthesis route driving redox-precipitation reactions among MnVII, CeIII and MnII precursors in basic aqueous solution yields MnCeO x catalysts (Mn loading, 9–33wt%) with improved textural and structural properties in comparison to the conventional co-precipitation technique. Irrespective of the Mn loading, BET, X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) findings prove that the new method ensures a very high reproducibility in all the main physico-chemical properties of MnCeO x catalysts. Enabling a monolayer dispersion of the active phase, the “redox-precipitation” method greatly promotes the reducibility and the surface affinity of the MnCeO x system towards gas-phase oxygen. [Copyright &y& Elsevier]

The working mechanism of a ceria-supported Cu (Cuat:Ceat = 1:10) system in the Catalytic Wet Oxidation (CWO) of phenol with O2 ( T R, 130–170 °C; P O 2, 7 atm) has been thoroughly assessed. Basic relationships amongst pH, extent of leaching and rate of phenol and TOC conversion prove the major contribution of a homogeneous catalytic path by Cu ions on the peculiar CWO pattern of supported copper catalyst. In addition, gas-phase reduction/oxidation tests signal the lack of reversibility of the redox cycle of the CuCeO x system under typical reaction conditions. [ABSTRACT FROM AUTHOR]

The pressing need to prevent further damages to environment and deterioration of natural resources urges a global effort to shift from the current money-making industrial policies to a sustainable development pattern. This requires an easy availability of handy and economical technologies for depollution of gas and liquid wastes, “green” industrial manufacturing processes and “zero-emission” energy supply systems. In this context the purification and reuse of industrial wastewaters represents a very critical environmental issue because of the global freshwater shortage, the continuing water resources depletion, and the increasing pollutants release. In this context, the heterogeneous catalytic wet air oxidation (CWAO) is nowadays considered the most promising technology for large-scale application to detoxification of noxious wastewaters, provided that robust, effective and cost-effective catalysts are available. Then, this work provides an overview of mechanistic and kinetic issues of the homogeneous and heterogeneous CWAO of several classes of industrial pollutants, at basis of recent advances on design and development of supported noble metal and oxide catalysts. [ABSTRACT FROM AUTHOR]

Abstract: Physicochemical properties and CO2-to-methanol hydrogenation functionality (T R, 453–513K; P R, 0.1–5.0MPa) of Al2O3-, ZrO2-, and CeO2-supported Cu–ZnO catalysts are systematically addressed. Carriers control texture and metal surface exposure (MSA), while characterization of steady-state catalysts shows extensive CO2 and H2 coverage regardless of MSA, proving a crucial influence of the oxide carrier on the adsorption properties of the Cu–ZnO system. The kinetic dependence on p CO2 and p H2 confirms that dioxo-methylene intermediate hydrogenation is the rate-determining step (r.d.s.) at P <0.1MPa, while a low kinetic dependence on pressure (0.3–0.5) signals that product desorption is the r.d.s. at P >0.1MPa. The influence of flow rate on selectivity pattern discloses that CH3OH is the primary reaction product at T <473K, while at higher temperatures, CO forms by consecutive decomposition of methanol (MD) and parallel reverse water–gas shift (RWGS). Textural and chemical effects of the zirconia carrier confer superior performance on the Cu–ZnO/ZrO2 system, attaining a space time yield (STY) of 1.2 at 10% conversion per pass. [Copyright &y& Elsevier]