David Chadwick

Adsorption of carbon dioxide on graphene oxide supported layered double oxides

AbstractnAdsorption of CO2 on layered double oxides supported on graphene oxide has been studied under dry and wet conditions. In the first exposure to the adsorptive gas, the isotherms obtained for supported and unsupported materials are shown to fit to the Freundlich model indicating the existence of heterogeneous adsorption sites. After multiple temperature-swing cycles, the adsorption capacity decreased and the data is better described by the Langmuir model. The presence of graphene oxide is shown to reduce the loss of adsorption capacity, and helps to maintain the heterogeneity of the basic sites on the adsorbents. The use of wet gas mixtures was found to have a positive effect on the CO2 adsorption capacity of the graphene oxide hybrids. The presence of residual sodium on the materials resulted in a Freundlich isotherm with increased adsorption capacity.

MFI Acid Catalysts with Different Crystal Sizes and Porosity for the Conversion of Furanic Compounds in Alcohol Media

Solid acid catalysts possessing MFI topology and different crystal sizes and porosities were explored for the conversion of carbohydrate‐biomass‐derived α‐angelica lactone and 5‐(hydroxymethyl)furfural, in 1‐butanol at T=120–170u2009°C, to give levulinate esters and furanic ethers. Micro/mesoporous microcrystalline catalysts were prepared by post‐synthesis base/acid treatments of ZSM‐5 zeolite; the influence of the desilication (base) conditions on the material properties was investigated. A nanocrystalline ZSM‐5 sample was synthesised by using hydrothermal, dynamic conditions and used as a reference material. A comparison of the catalytic performances of materials featuring different morphological, textural, and acid properties highlights a complex interplay between the acid and textural properties. The best‐performing catalyst (MZS0.6) was obtained by post‐synthesis‐treatment; fairly good catalytic stability was confirmed by catalyst recycling, contact tests, and characterisation of the spent catalyst. MZS0.6 was compared with the macrorecticular ion‐exchange resin Amberlyst‐15, chosen as a benchmark solid acid catalyst, in the two reaction systems.

Au-Pd Bimetallic Nanoparticles Immobilised on Titanate Nanotubes: A Highly Active Catalyst for Selective Oxidation

In this work, a highly active Au‐Pd/Ti‐NT catalyst has been produced by using colloidal synthesis and immobilisation on essentially sodium‐free Ti‐nanotubes (NTs). The new catalyst has markedly superior catalytic activity (turnover frequency>19u2009000u2005h−1) for the selective oxidation of benzyl alcohol compared with similar catalysts reported in the literature, and to Au‐Pd catalysts supported on Ti‐NTs prepared by adsorption, as well as conventional Au‐Pd/TiO2 prepared by impregnation. The superior catalytic activity of the catalyst is shown to be a result of the high metal dispersion on the external surfaces of Ti‐NTs, the narrow particle size distribution and the consistent formation of Au‐Pd mixed alloy nanoparticles in close to a 1:1 weight ratio. In repeated use, the Au‐Pd/Ti‐NT catalyst showed only a modest fall in activity, which is shown by FTIR to be associated mainly with the irreversible adsorption of benzoic acid and benzyl benzoate by the catalyst.

Thermodynamic Analysis of Autothermal Reforming of Oxygenated Hydrocarbons at Thermoneutral Condition for Hydrogen Production

The thermodynamic analysis of autothermal reforming of homologue series consisted of ethanol, ethylene glycol, propylene glycol and glycerol representing oxygenated hydrocarbons were studied. The main investigation was to compare the effect of thermoneutral condition where no external air/oxygen supplied for the reaction to sustain and controlled amount of air/oxygen supplied. It was found that the higher number of oxygen atoms in these homologues molecule, the higher tendency of the reaction to be sustained at the desired temperature, and thus it only requires lesser amount of air for heating. The hydrogen selectivity however depends on the ratio of hydrogen atoms with respect to the oxygen atoms in each molecule. The presence of air however, though providing extra heating to the reactor, is offset by a lower hydrogen production.

Au–Pd NPs immobilised on nanostructured ceria and titania: impact of support morphology on the catalytic activity for selective oxidation

Bimetallic Au–Pd nanoparticles supported on different ceria and titania nanostructures have been prepared by sol-immobilisation, and evaluated in the solvent-less selective oxidation of benzyl alcohol. The catalysts were characterised by TEM, STEM, XRD, XPS, ICP-AES, and nitrogen adsorption–desorption measurements. The activity of the catalysts was found to be strongly related to the morphology, structure and physiochemical properties of the supports. Au–Pd/ceria nanorods exhibited remarkably high catalytic activity (TOF > 35u2006900 h−1), and was found to be considerably more active than Au–Pd/titanate nanotubes, and Au–Pd catalysts supported on conventional ceria and titania nanopowders. The outstanding catalytic performance of Au–Pd/ceria nanorods is attributed to the unique surface chemistry of ceria nanorods, and the ability of catalyst preparation method (i.e. sol-immobilisation) to control the metal particle size and the bimetallic alloy formation. The presence of surface defects and high concentration of oxygen vacancies and Ce3+ in ceria nanorods is likely responsible for the stabilisation of Au–Pd NPs during sol-immobilisation, which led to a very small mean particle size (2.1 nm) corresponding to a dispersion of approximately 52%, and a high surface metal concentration.

Selective Oxidation of Methane to Methanol over ZSM-5 Catalysts in Aqueous Hydrogen Peroxide: Role of Formaldehyde

The selective oxidation of methane in aqueous hydrogen peroxide over ZSM‐5 catalysts with different Si/Al ratios has been investigated. Methyl hydroperoxide was confirmed as the initial product of methane oxidation by a study of product distribution versus reaction time in agreement with previous work. Formaldehyde was identified as an intermediate in the oxidation reaction pathway from MeOOH to formic acid and ultimately CO2. Hydrogen evolution during the oxidation of methane is reported for the first time. Oxidation of the HCHO intermediate to formic acid was demonstrated to be the source of the evolved hydrogen. HCHO appeared to be the source of low levels of soluble polyoxomethylene. Higher productivity of liquid oxygenated products is reported compared to previous work.

Ethanol Steam Reforming over Calcium Doped Ni/Al2O3 Catalyst

Steam reforming of ethanol has been carried out using a commercial catalyst (Hi-FUEL) of calcium doped nickel/alumina catalyst. Hi-FUEL had successfully reformed ethanol into the desired products at relatively high yield and selectivity. The hydrogen yield of 90.5% has been achieved from this catalyst with almost no ethylene detected. Hi-FUEL is also comparable with other calcium doped nickel/alumina catalyst as reported by other researchers.