Ammonia decomposition enhancement by Cs-Promoted Fe/Al2O3 catalysts

A range of Cs-doped Fe/Al2O3 catalysts were prepared for the ammonia decomposition reaction. Through time on-line studies it was shown that at all loadings of Cs investigated the activity of the Fe/Al2O3 catalysts was enhanced, with the optimum Cs:Fe being ca. 1. Initially, the rate of NH3 decomposition was low, typically < 10% equilibrium conversion (99.7%@500°C) recorded after 1 h. All catalysts exhibited an induction period (typically ca. 10 h) with the conversion reaching a high of 67% equilibrium conversion for Cs:Fe = 0.5 and 1. The highest rate of decomposition observed was attributed to the balance between increasing the concentration of Cs without blocking the active site. Analysis of H2-TPR and XPS measurements indicated that Cs acts as an electronic promoter. Previously, Cs has been shown to act as a promoter for Ru, where Cs alters the electron density of the active site, thereby facilitating the recombination of N2 which is considered the rate determining step. In addition, XRD and N2 adsorption measurements suggest that with higher Cs loadings deactivation of the catalytic activity is due to a layer of CsOH that forms on the surface and blocks active sites

Using real particulate matter to evaluate combustion catalysts for direct regeneration of diesel soot filters

The particulate produced by internal combustion engines has a complex composition that includes a large proportion of porous soot within which condensed and adsorbed organic molecules are trapped. However, many studies of the catalytic combustion of particulate are based on the assumption that commercially produced carbon can be used as a reliable mimic of engine soot. Here we show that soot removed from a diesel particulate filter is rich in the polyaromatic molecules that are the precursors of the solid particulate. Through a combination of solvent extraction and evolved gas analysis, we have been able to track the release and transformation of these molecules in the absence and presence of combustion catalysts. Our results reveal that, although the rate of combustion of the elemental carbon in diesel soot is higher than that of graphite, deep oxidation of the polyaromatic molecules is a more demanding reaction. An active and stable Ag–K catalyst lowers the combustion temperature for elemental carbon by >200 °C, but has little effect on the condensed polyaromatic molecules. The addition of a secondary catalyst component, with aromatic-oxidation functionality is required to target these molecules. Although the combined catalyst would not enable a completely passive regeneration system for diesel passenger cars, it would improve the efficiency of existing active systems by reducing the amount of fuel-injection required for trap regeneration

The surface of iron molybdate catalysts used for the selective oxidation of methanol

The oxidation of methanol to formaldehyde is a major chemical process carried out catalytically and iron molybdate is one of the major catalysts for this process. In this paper we explore the nature of the active and selective surfaces of iron molybdate catalysts and show that the effective catalysts comprise molybdenum rich surfaces. We conclude that it is therefore important to maximise the surface area of these active catalysts and to this end we have studied catalysts made using a new physical grinding method with oxalic acid. For super-stoichiometric materials (Fe:Mo = 1:2.2) the reaction data show that physical mixing produces effective catalysts, possibly offering an improvement over the conventional co-precipitation method

Effect of the preparation method of LaSrCoFeOx perovskites on the activity of N2O decomposition

N2O remains a major greenhouse gas and contributor to global warming, therefore developing a catalyst that can decompose N2O at low temperatures is of global importance. We have investigated the use of LaSrCoFeOx perovskites for N2O decomposition and the effect of surface area, A and B site elements, Co–O bond strength, redox capabilities and oxygen mobility have been studied. It was found that by using a citric acid preparation method, perovskites with strong redox capabilities and weak Co–O bonds can be formed at relatively low calcination temperatures (550 °C) resulting in highly active catalysts. The enhanced activity is related to the presence of highly mobile oxygen species. Oxygen recombination on the catalyst surface is understood to be a prominent rate limiting step for N2O decomposition. Here the reduced strength of Co–O bonds and mobile lattice oxygen species suggest that the surface oxygen species have enhanced mobility, aiding recombination, and subsequent regeneration of the active sites. La0.75Sr0.25Co0.81Fe0.19Ox prepared by citric acid method converted 50% of the N2O in the feed (T50) at 448 °C

Lowering the operating temperature of perovskite catalysts for N2O decomposition through control of preparation methods

Discovering catalysts that can decompose N2O at low temperatures represents a major challenge in modern catalysis. The effect of preparative route on N2O-decomposition activity has been examined for a PrBaCoO3 perovskite catalyst. Initially, a citric acid preparation was utilised where the A site ratio was altered in order to increase phase purity. Comparable compositions were then prepared by an oxalic acid precipitation method and by a supercritical anti-solvent technique to produce perovskites with a higher surface area (> 30 m2g-1). By altering the A site ratios it was possible to reduce the temperature required to produce a pure phase perovskite whilst maintaining a higher-surface area. The use of the different preparation methods resulted in perovskites with varying properties, as determined by N2 adsorption, XPS and O2-TPD. This work confirms the importance of lattice oxygen species that have high oxygen mobility for enhanced decomposition of N2O, as oxygen recombination is considered the rate-limiting step. Here, the formation of molecular oxygen is limited by surface adsorbed O species being within a distance at which oxygen recombination is possible. The most active PrBaCo-based catalyst did not have the highest percentage of lattice oxygen as shown by XPS, however, the catalytic activity could be correlated to the mobile oxygen species and high surface area. The PrBaCo-based catalyst prepared by supercritical anti-solvent converted 50 % of the N2O present in the feed (T50) at 410 °C, which represents a significant improvement over reported catalytic performance measured under similar conditions

Investigating periodic table interpolation for the rational design of nanoalloy catalysts for green hydrogen production from ammonia decomposition

Developing highly active catalysts for the decomposition of ammonia to produce hydrogen is an important goal in the context of renewable energy. Allied with this is a need for identification strategies to efficiently design novel catalysts integral to ensuring rapid progress in this research field. We investigated the efficacy of N–binding energy and periodic table interpolation to predict active bimetallic nanoparticle catalysts. Supported iron-platinum and iron-palladium were identified and experimentally shown to be more active than their monometallic analogues. Atomic resolution electron microscopy indicated that the most active catalyst (5 wt% Fe80Pt20/γ-Al2O3) was principally formed of alloyed nanoparticles. It restructured during testing, yet no activity loss was noted at 20 h time-on-line. While these findings show that periodic table interpolation may be a viable tool for identifying active combinations of metals, the activity of the catalysts in the current work were not able to outperform the Ru/Al2O3 benchmark. Further catalyst optimization or refinement of reaction descriptors may facilitate the development of catalysts with higher intrinsic activity than the current state-of-the-art catalysts

What is the point of on-board fuel reforming?

On-board autothermal reforming, which had been intended for mobile fuel cell applications, has evolved into exhaust gas reforming—a technology that could make it more difficult for the internal combustion engine to be displaced. Among the technical barriers that prevented implementation of fuel cell drivetrains based on autothermal reforming was the integration of several chemical processes into an energy- and space-efficient system with a high degree of heat management. By contrast, an exhaust gas reformer bears much more resemblance to the passive catalytic converters used for exhaust-gas after treatment, except that it is located in a recirculation loop close to the engine. When the reactions are predominantly endothermic, the reformer recovers waste heat and generates reformate with a higher fuel heating value than that of the fuel it consumes. The reformate does not need any further treatment, but can be fed directly to the engine, where it will have an additional impact on fuel economy by acting as a gas-phase combustion promoter. On-board reforming also increases the number of potential after treatment options, some of which are substantially improved by the addition of hydrogen

Final analysis: Catalysis "after the goldrush"

Cardiff University, UK, has recently been awarded European Union (EU) funding for a new programme entitled “After the Goldrush” (1). This programme aims to explore the implications of discoveries made over the last 25 years of intensive research into catalysis by gold and so accelerate the discovery and development of other catalytic materials such as those based on platinum group metals (pgms), which may hold the key to solving many of the pressing challenges facing us now and in the future

Final analysis: Catalysis "after the goldrush"

Cardiff University, UK, has recently been awarded European Union (EU) funding for a new programme entitled “After the Goldrush” (1). This programme aims to explore the implications of discoveries made over the last 25 years of intensive research into catalysis by gold and so accelerate the discovery and development of other catalytic materials such as those based on platinum group metals (pgms), which may hold the key to solving many of the pressing challenges facing us now and in the future