Support Induced Effects on the Ir Nanoparticles Activity, Selectivity and Stability Performance under CO2 Reforming of Methane.

The production of syngas (H2 and CO)-a key building block for the manufacture of liquid energy carriers, ammonia and hydrogen-through the dry (CO2-) reforming of methane (DRM) continues to gain attention in heterogeneous catalysis, renewable energy technologies and sustainable economy. Here we report on the effects of the metal oxide support (γ-Al2O3, alumina-ceria-zirconia (ACZ) and ceria-zirconia (CZ)) on the low-temperature (ca. 500-750 ∘C) DRM activity, selectivity, resistance against carbon deposition and iridium nanoparticles sintering under oxidative thermal aging. A variety of characterization techniques were implemented to provide insight into the factors that determine iridium intrinsic DRM kinetics and stability, including metal-support interactions and physicochemical properties of materials. All Ir/γ-Al2O3, Ir/ACZ and Ir/CZ catalysts have stable DRM performance with time-on-stream, although supports with high oxygen storage capacity (ACZ and CZ) promoted CO2 conversion, yielding CO-enriched syngas. CZ-based supports endow Ir exceptional anti-sintering characteristics. The amount of carbon deposition was small in all catalysts, however decreasing as Ir/γ-Al2O3 > Ir/ACZ > Ir/CZ. The experimental findings are consistent with a bifunctional reaction mechanism involving participation of oxygen vacancies on the support's surface in CO2 activation and carbon removal, and overall suggest that CZ-supported Ir nanoparticles are promising catalysts for low-temperature dry reforming of methane (LT-DRM)

Ir-Catalysed Nitrous Oxide (N2O) Decomposition:Effect of Ir Particle Size and Metal–Support Interactions

The effect of the morphology of Ir particles supported on γ-Al2O3, 8 mol%Y2O3-stabilized ZrO2 (YSZ), 10 mol%Gd2O3-doped CeO2 (GDC) and 80 wt%Al2O3–10 wt%CeO2–10 wt%ZrO2 (ACZ) on their stability on oxidative conditions, the associated metal–support interactions and activity for catalytic decomposition of N2O has been studied. Supports with intermediate or high oxygen ion lability (GDC and ACZ) effectively stabilized Ir nanoparticles against sintering, in striking contrast to supports offering negligible or low oxygen ion lability (γ-Al2O3 and YSZ). Turnover frequency studies using size-controlled Ir particles showed strong structure sensitivity, de-N2O catalysis being favoured on large catalyst particles. Although metallic Ir showed some de-N2O activity, IrO2 was more active, possibly present as a superficial overlayer on the iridium particles under reaction conditions. Support-induced turnover rate modifications, resulted from an effective double layer [Oδ−–δ+](Ir) on the surface of iridium nanoparticles, via O2− backspillover from the support, were significant in the case of GDC and ACZ

Chemical Cogeneration in Solid Electrolyte Cells The Oxidation of H2S to S02

ABSTRACT The anodic oxidation of H2S was investigated in the solid electrolyte fuel cell H2S, Sx, SO2, Pt/ZrO2(8% Y~O3)/Pt, air operating at atmospheric pressure and temperatures 650 ~ to 800~ It was found that the fuel cell product selectivity crucially depends on the ratio M of the fluxes of oxygen anions 02_ and H2S reaching the porous Pt anode. When M < 0.33, elemental sulfur is the major product, and the anode is severely polarized. For higher M values, the product selectivity to SO2 exceeds 99% at H2S conversions as high as 99%. The cell appears to be a promising candidate for the cogeneration of electric energy and sulfur dioxide. The oxidation of hydrogen sulfide to sulfur dioxide is one of the basic steps of the Claus process and, ultimately, of the industrial manufacture of sulfuric acid, which ranks first in volume among all chemicals produced with an annual worldwide production exceeding 3 -108 tons. The conversion of H2S to SO2 is a highly exothermic reaction with AG ~ = -103,6 kcal/mole SO2 at 800~ Due to the high exothermicity of the reaction, large amounts of thermal energy are generated. It has been a long-sought goal to obtain this energy as electric rather than thermal energy by oxidizing H2S to SO2 in a fuel cell (1, 2). Low-temperature fuel cells are severely polarized by H2S and: sulfur. High-temperature solid electrolyte cells have been tested for years as fuel cells with H2, CO, or CH4 as the fuel (3-8). The same:type of cells can be used to study the mechanism of catalytic reactions on metals (9-12) and also to influence the activity and selectivity of metal catalysts by electrochemically pumping oxygen anions O 2-onto catalyst surfaces (13-17). Progress in this area has been reviewed recently (18). In some very recent studies (17,(19)(20)(21) it has been found that the increase in catalytic reaction rate can exceed the rate of 02 pumping to the catalyst by as much as a factor of l0 s with a concomitant 40-fold increase in catalytic reaction rate over its open-circuit value (19)(20). The acronym NEMCA (non-faradaic electrochemical modification of catalytic activity) has been used to describe this new phenomenon which has been attributed to changes induced to the average catalyst work function due to the interaction of the catalyst surface with excess 02 (17,(19)(20)(21). One of the emerging uses of solid electrolyte cells is chemical cogeneration, i.e., the simultaneous production of electrical power and useful chemicals. This mode of operation combines the concepts of a fuel cell and of a chemical reactor. Its feasibility was first demonstrated in 1980 when it was shown that solid oxide fuel cells with Pt-based electrodes can quantitatively convert NH3 to NO with simultaneous generation of electrical power (22)(23)(24). Subsequent work has shown that four other exothermic reactions of industrial importance can also be carried out successfully in solid oxide fuel cell reactors with appropriate electrocatalytic anodes. These are the oxidative dehydrogenation of ethylbenzene to styrene (25, 26) and l-butene to butadiene (27), the Adrussov process, i.e., the ammoxidation of methane to form HCN (28) and, more recently, the partial oxidation of methanol to formaldehyde (18, There have been two very recent studies of the anodic oxidation of H2S in high-temperature yttria-stabilized zirconia cells In this work, H2S was used as the fuel in a high-temperature solid electrolyte fuel cell with porous Pt electrodes in order to study the electrochemical characteristics and product distribution of the cell and explore the possibility of simultaneous generation of SO2 and electrical power. Experimental Apparatus A schematic diagram of the experimental apparatus, which has been described in previous communications (9-12, 17, 24), is shown i

The Role of Alkali and Alkaline Earth Metals in the CO2 Methanation Reaction and the Combined Capture and Methanation of CO2

CO2 methanation has great potential for the better utilization of existing carbon resources via the transformation of spent carbon (CO2) to synthetic natural gas (CH4). Alkali and alkaline earth metals can serve both as promoters for methanation catalysts and as adsorbent phases upon the combined capture and methanation of CO2. Their promotion effect during methanation of carbon dioxide mainly relies on their ability to generate new basic sites on the surface of metal oxide supports that favour CO2 chemisorption and activation. However, suppression of methanation activity can also occur under certain conditions. Regarding the combined CO2 capture and methanation process, the development of novel dual-function materials (DFMs) that incorporate both adsorption and methanation functions has opened a new pathway towards the utilization of carbon dioxide emitted from point sources. The sorption and catalytically active phases on these types of materials are crucial parameters influencing their performance and stability and thus, great efforts have been undertaken for their optimization. In this review, we present some of the most recent works on the development of alkali and alkaline earth metal promoted CO2 methanation catalysts, as well as DFMs for the combined capture and methanation of CO2