Michael S. Scurrell

Thoughts on the use of gold-based catalysts in environmental protection catalysis

Gold catalysts can exhibit a very high low-temperature activity for the oxidation of carbon monoxide and can be selective in the presence of hydrogen. This paper aims to discuss the prospects for gold-based catalysts to operate in autocatalyst exhaust treatment systems by reviewing very recent results which suggest that the long-sought-after high thermal stabilization of nanogold particles may be within reach. It discusses the CO oxidation reaction at high temperature together with reflections on hydrocarbon total oxidation and the reduction of nitric oxide by carbon monoxide and hydrocarbons. The practical means to achieve high-temperature stability are discussed together with options for enhancing the catalytic activity of gold, based on the extensive amount of work which has now been recorded for low-temperature operations. The potential for thrifting gold is also discussed together with a rough assessment of economic factors which appear to make gold a more attractive metal for this application than the established platinum group elements.

Carbon Surface Modifications by Plasma for Catalyst Support and Electrode Materials Applications

Plasma has been introduced in recent years as a promising method for modification of carbon materials in comparing with traditional wet chemical method, thanks to reduced energy combustion, shortened synthesis duration and undestroyed bulk structure. In this review, we present the modification of carbons on surface chemistry and the recent progress in the applications of these modified carbons in catalyst supports and electrode materials. Plasma methods show promise as a means of enhancing surface properties without destroying the bulk structure of the carbon. Interaction can occur with oxygen, nitrogen and halogens and the chemical modification at the surface can often lead to the provision of sites that can be used to anchor small (nano) particles of metals and active components. This in turn can lead to enhanced catalytic behavior, including electrocatalysis. Hydrophilic/hydrophobic properties can also be tuned via this approach, Carbons modified in this way have also shown promise as high performance electrode materials and pseudocapacitors. The review also mentions challenges and opportunities for further modification of carbons by plasma treatment and for broadening their applications.

Microwave treatment: a facile method for the solid state modification of potassium-promoted iron on silica Fischer–Tropsch catalysts

Potassium-promoted (0–1.5 wt%) iron–silica catalysts for Fischer–Tropsch synthesis (FTS) have been modified using microwave radiation. Radiation produced few or no modifications in the bulk properties, but surface and catalytic behaviour were markedly changed in K promoted 10 wt% of Fe/SiO2 (10Fe/SiO2) catalysts. The effect of potassium on CO adsorption was relatively insignificant in untreated catalysts, but was large in microwave-modified catalysts. Radiation induced an increase in CH4 formation in CO + H2 temperature programmed surface reactions. Microwave treatment promoted CH4 formation from graphitic carbon in these catalysts, while decreasing CH4 formation from α- and β-carbon species, and overall favoured strong CO adsorption onto the catalyst surface. Microwave effects were catalyst particle size and treatment duration-dependent. At low alkali concentration, microwaved samples showed improved ethene selectivities, higher alpha values and lower methane and light alkene selectivities. When 0.7 wt% K was added to the 10Fe/SiO2 catalyst, the α value increased from 0.59 to 0.66 after treatment of the sample with microwave radiation in the solid state.

Effect of Fe on the activity of Au/FeOx-TiO2 catalysts for CO oxidation

A thorough characterisation of Au/TiO2 and Au/FeOx-TiO2 catalysts was conducted in order to get a better understanding of the effect of Fe on the Au/TiO2 catalysts and link it to differences observed in their activities for CO oxidation. Several techniques including HRTEM, temperature-programmed reduction (TPR), UV-Vis and temperature-programmed desorption (TPD) of isopropyl amine, CO and CO2 were used to characterise the catalysts. Au/FeOx-TiO2 (300xa0°C), which was found to be the most active catalyst for CO oxidation, had the highest number of Brønsted acid sites, although its concentration of Lewis acid sites was similar to all other tested catalyst systems. X-ray photoelectron spectroscopy (XPS) revealed that the Fe species on the Au/FeOx-TiO2 catalyst is Fe2+ with a very small amount of Fe3+. Fe2+ is comprised of both FeO and Fe3O4 species, and according to TPR, the ratio (FeO/Fe3O4) between these two species increases with increasing calcination temperature. The presence of Fe on the Au/TiO2 catalyst seems to stabilise the Au nanoparticles from agglomeration. The activation energy of desorption (Ed) of CO from Au/FeOx-TiO2 (300xa0°C) was 82.7xa0kJ/mol, whilst on Au/TiO2, the Ed for CO was 108.8xa0kJ/mol. On both catalysts, the Ed for CO2 was ca. 99xa0kJ/mol.

Catalytic activity of gold-perovskite catalysts in the oxidation of carbon monoxide

AbstractPerovskites (ABO3 structures), which can be manipulated by partial substitution, are reported to be active supports for CO oxidation, but only at high temperatures, with no activity being shown for temperatures below 200xa0°C. In this study, these perovskites were investigated at low temperatures (below 100xa0°C) with improved activity found upon gold deposition. The presence of gold nanoparticles therefore significantly enhanced the catalytic activity, while the support itself was suspected to be involved in the reaction mechanism. A series of perovskites of the type ABO3 (LaMnO3, LaFeO3, LaCoO3, and LaCuO3) were prepared using the citrate method, while the gold was deposited on them using the deposition-precipitation method. The supports were calcined at different temperatures for optimization. With the support calcined at 800xa0°C, the best catalyst was 1xa0wt% Au supported on LaFeO3. Calcium-doping of this system showed decreased surface area, poorer crystallinity, and a drop in catalytic activity relative to the Au-LaFeO3. In addition, Au-LaFeO3 showed online stability over 21xa0h. Calcining the support improved the incorporation of gold nanoparticles into the perovskite lattice, resulting in superior catalytic activity. Nevertheless, at higher calcination temperatures, the catalytic activity of Au-CaTiO3 was depressed while that of Au-LaFeO3 was enhanced. XPS revealed that in the active catalysts, both cationic and metallic gold coexisted, while in the inactive catalysts, the gold existed predominantly either as cationic or metallic gold.n Graphical abstractGold-perovskites offer activity as high as that reported for other systems, notably gold-titania catalysts for CO oxidation

Cold plasmas in the modification of catalysts

Abstract Heterogeneous catalysts play an important role in the chemical industry and are also of critical importance in the general well-being of society in the 21st century. Increasing demands are being placed on catalyst performance in a number of areas such as activity, selectivity, longevity, and cost. Conventional approaches to improving catalytic performance are becoming exhausted, and novel ways of generating the increased performance are being sought. The utilization of cold plasmas has opened great opportunities for modification of catalysts, thanks to their room-temperature operations with reduced energy combustion, shortened duration, and undestroyed bulk structure. In this review, we present an assessment of the modification of catalysts by cold plasmas, with emphasis on particle sizes, dispersion of nanoparticles, distribution of elements, electronic properties, acid-base properties, surface functional groups, and metal-support interaction. Moreover, challenges and perspectives are also presented for the further modification of catalysts by cold plasmas and broadening their practical applications.

Enhanced photocatalytic hydrogen formation over Fe-loaded TiO2 and g-C3N4 composites from mixed glycerol and water by solar irradiation

Fe-doped TiO2 with various levels of Fe (0.5, 1, 2, 3, and 5u2009wt. %) was made via impregnation, and the Fe-doped TiO2 catalysts were modified with g-C3N4. These materials were studied using FE-SEM, Uv-DRS, TEM, Raman, FT-IR, and XPS techniques. The results show that the fine dispersed Fe3+ and g-C3N4 expanded the photoresponse of titania into the visible region on the introduction of ferric ions and fine dispersion of g-C3N4 on TiO2. The hydrogen formation rate from solar light-induced photocatalysis can be greatly increased by coupling g-C3N4 with the above Fe-doped TiO2, and the 1u2009wt. % Fe-modified TiO2 with the g-C3N4 composite has high photoactivity and shows excellent photostability for hydrogen production by solar irradiation. The stable hydrogen evolution of 1u2009wt. % Fe-doped TiO2 with g-C3N4 is some 17 times higher than that found with unmodified TiO2. The results show that the photogenerated electrons of g-C3N4 can directionally migrate to Fe-doped TiO2 due to intimate interfacial contacts and synergism operating between Fe-doped TiO2 and g-C3N4 where photogenerated electrons and holes are efficiently spatially separated. This separation retards the charge recombination rate and improves photoactivity.Fe-doped TiO2 with various levels of Fe (0.5, 1, 2, 3, and 5u2009wt. %) was made via impregnation, and the Fe-doped TiO2 catalysts were modified with g-C3N4. These materials were studied using FE-SEM, Uv-DRS, TEM, Raman, FT-IR, and XPS techniques. The results show that the fine dispersed Fe3+ and g-C3N4 expanded the photoresponse of titania into the visible region on the introduction of ferric ions and fine dispersion of g-C3N4 on TiO2. The hydrogen formation rate from solar light-induced photocatalysis can be greatly increased by coupling g-C3N4 with the above Fe-doped TiO2, and the 1u2009wt. % Fe-modified TiO2 with the g-C3N4 composite has high photoactivity and shows excellent photostability for hydrogen production by solar irradiation. The stable hydrogen evolution of 1u2009wt. % Fe-doped TiO2 with g-C3N4 is some 17 times higher than that found with unmodified TiO2. The results show that the photogenerated electrons of g-C3N4 can directionally migrate to Fe-doped TiO2 due to intimate interfacial contacts and syne...

Selective CO Methanation Over Ru Supported on Carbon Spheres: The Effect of Carbon Functionalization on the Reverse Water Gas Shift Reaction

Mesoporous carbon spheres (CSs-H) were hydrothermally synthesised using sugar as carbon source. The as-synthesized CSs-H was microporous but after thermal treatment at 900xa0°C for 4xa0h it became mesoporous (surface area of 463xa0m2xa0g−1). Further treatment of the annealed CSs-H with HNO3 gave a functionalized CSs-H with a high defect content in the carbon matrix which resulted in an increase in surface area (509xa0m2xa0g−1). The functionalized and un-functionalized CSs-H were used to support nano Ru particles for CO, CO2 and selective CO methanation reactions. The Ru supported catalysts were prepared using both impregnation and microwave polyol synthesis methods. It was evident from the reduction studies that the functional groups on the surface of the CSs-H influenced the reduction of the RuO2 to Ru. The catalyst with smaller and well dispersed RuO2 particles (du2009=u20092.7xa0nm) (prepared by the microwave polyol technique) gave a high activity in both CO and selective CO methanation studies. The larger Ru particles observed on the un-functionalized CSs-H showed poor activity for CO and selective CO methanation reactions and also did not promote the reverse water gas shift reaction.Graphical Abstract

The Conversion of Methanol into Higher Hydrocarbons Catalyzed by Gold

Gold/zinc oxide catalysts prepared by coprecipitation and containing gold particles of approximately 6u2005nm in diameter are active in the conversion of methanol to higher hydrocarbons under mild conditions. Conversions exceed 97u2009% under the selected experimental conditions at reaction temperatures of 350u2009°C, with a turnover number of 0.02u2005s−1. Both alkanes and alkenes up to C6 are formed, with a selectivity of approximately 44u2009%C hydrocarbons and 56u2009%C dimethyl ether. The addition of zeolite‐Y in composite catalysts modifies the product spectrum slightly. Ethene and propene dominate the alkenes formed above 450u2009°C if a 1:1 HY:Au/ZnO composite is used; the dominant alkane under these conditions is methane. At 475u2009°C only three hydrocarbons are present with selectivities of 13 (methane), 39 (ethene), and 48u2009% (propene). The carbon−carbon bond formation was not seen in earlier work when syngas (CO plus H2) was converted with the same Au/ZnO catalyst at high pressure to form mixtures of alcohols and hydrocarbons. This suggests that the formation of higher hydrocarbons from methanol is inhibited in the presence of CO and/or H2, probably due to competitive CO adsorption on the gold surface.