Catalytic combustion: from reaction mechanism to commercial applications

Catalytic Hydrogen Combustion for Domestic and Safety Applications: A Critical Review of Catalyst Materials and Technologies

Spatial heating and cooking account for a significant fraction of global domestic energy consumption. It is therefore likely that hydrogen combustion will form part of a hydrogen-based energy economy. Catalytic hydrogen combustion (CHC) is considered a promising technology for this purpose. CHC is an exothermic reaction, with water as the only by-product. Compared to direct flame-based hydrogen combustion, CHC is relatively safe as it foregoes COx, CH4, and under certain conditions NOx formation. More so, the risk of blow-off (flame extinguished due to the high fuel flow speed required for H2 combustion) is adverted. CHC is, however, perplexed by the occurrence of hotspots, which are defined as areas where the localized surface temperature is higher than the average surface temperature over the catalyst surface. Hotspots may result in hydrogen’s autoignition and accelerated catalyst degradation. In this review, catalyst materials along with the hydrogen technologies investigated for CHC applications were discussed. We showed that although significant research has been dedicated to CHC, relatively limited commercial applications have been identified up to date. We further showed the effect of catalyst support selection on the performance and durability of CHC catalysts, as well as a holistic summary of existing catalysts used for various CHC applications and catalytic burners. Lastly, the relevance of CHC applications for safety purposes was demonstrated.

Catalytic combustion of propane on Pd-modified Al–La–Ce catalyst – from reaction kinetics and mechanism to monolithic reactor tests and scale-up

A propane combustion catalyst was prepared by supporting of Pd on optimized multiphase composition, containing Al2O3, La2O3 and CeO2 aiming for possible application in catalytic converters for abatement of propane in waste gases. The catalyst characterization has been made by N2- physisorption, XRD, SEM/EDX, TEM and XPS. The obtained values for reaction order towards propane and oxygen are 0.57 and 0.14, respectively. The negative reaction order towards the water vapour (−0.26) shows an inhibition effect of the water molecules. According to the kinetics model calculations, the reaction pathway over Pd-modified La–Ce catalyst proceeds most probably through Langmuir–Hinshelwood mechanism with adsorption of propane and oxygen on different types of sites, dissociative adsorption of oxygen, whereupon water molecules compete with propane molecules for one and the same type of adsorption sites. For practical evaluation of the synthesized material, a sample of Pd/Al2O3–La2O3–CeO2, supported on rolled Al-containing stainless steel (Aluchrom VDM®) to form a single monolithic channel was prepared and tested. Two-dimensional heterogeneous models were used to simulate the propane combustion from laboratory reactor to full-scale adiabatic monolithic converter for ensuring an effective abatement of propane emissions.

Investigation of Parameters Influencing the Activation of a Pd/γ-Alumina Catalyst during Methane Combustion

The progressive activation of a Pd(2 wt %)/gamma-alumina catalyst under the reaction conditions of catalytic combustion of methane (CCM) was studied. The reasons of this activation were investigated by XPS, CO-chemisorption, and HR-TEM. The removal of carbon from the surface cannot explain the observed activation process. Sintering of the palladium particles was detected but this parameter alone does not fully explain the activation process of the catalyst. HR-TEM imaging evidences (i) that PdO is present both in the fresh and the active catalyst and (ii) that the PdO nanoparticles sinter and restructure (surface roughening) during the reaction. Development of preferential faces was not observed. It is suggested that this restructuring may be responsible for the activation process by facilitating the formation of an active oxygen layer on the PdO surface. CCM on Pd/gamma-Al(2)O(3) depends on the thermal history of the catalyst and is a structure-sensitive reaction.