Initiator-free hydrocarbon oxidation using supported gold nanoparticlec

In the catalytic oxidation of cycloalkenes and linear internal alkenes using oxygen radical initiators are not required if the stabilisers are removed prior to reaction.</p

Deactivation studies of a carbon supported AuPt nanoparticulate catalyst in the liquid-phase aerobic oxidation of 1,2-propanediol

The aerobic oxidation of 1,2-propanediol in alkaline aqueous solvent over bimetallic AuPt/C catalysts has been studied and catalyst reusability has been assessed. A systematic decrease of catalytic conversion was observed after each reuse of the catalyst. In order to understand the causes of deactivation, the catalyst samples were characterised by N2 adsorption, temperature-programmed oxidation (TPO) and pulsed-field gradient nuclear magnetic resonance (PFG-NMR) diffusion measurements. The results revealed that the catalyst surface area and pore volume decrease significantly after each reuse of the catalyst. The intra-particle diffusion is characterised by two distinct diffusion regimes, a fast regime with self-diffusivities of 10−9–10−11 m2 s−1 and a slow diffusion regime, with values of self-diffusivities on the order of 10−11–10−13 m2 s−1. Self-diffusivity in the fast regime is assigned to diffusion within the mesoporous space of the catalyst. Self-diffusivity in the slow diffusion region is assigned to diffusion within the microporous space and decreases after each reuse of the catalyst in a trend similar to that of pore volume, suggesting that changes in catalyst porosity and pore structure affect molecular mobility within the micropores. TPO studies of these systems showed a different distribution of oxidation products in the reused catalyst samples compared to the fresh catalyst, which suggests changes of the combustion mechanism. Altogether, the results reveal that catalyst deactivation is caused by deposition and build-up of heavy molecular species on the catalyst surface, which reduce the catalyst porosity by pore blockage and narrowing of channels, which in turn affects the diffusion rate within the micropores

Understanding the Solvent Effect on the Catalytic Oxidation of 1,4-Butanediol in Methanol over Au/TiO2 Catalyst: NMR Diffusion and Relaxation Studies

The solvent effect on the catalytic oxidation of 1,4-butanediol over gold nanoparticles supported on titania (Au/TiO2) has been assessed and a detrimental effect on the reaction rate upon water addition to the initial methanol solvent was observed (see figure). NMR diffusion and relaxation studies revealed that water addition leads to a significant decrease of the diffusion coefficient and adsorption strength of the reactant over the catalyst surface, which in turn affects the reaction rate of the process

Nanoporous aluminosilicate mediated synthesis of 2- and 2,2-substituted 2,3-dihydroquinazolin-4(1H)-ones

Nanoporous silicate materials, made by an operationally simple evaporation-induced self-assembly (EISA) approach, efficiently catalyze the formation of 2-substituted 2,3-dihydroquinazolin-4(1H)-ones from aldehydes and dimethyl acetals. This methodology can be extended to encompass the reaction of ketones and ketals to provide facile access to 2,2-disubstituted and spiro dihydroquinazolin-4(1H)-ones in high yields and short reaction times

Supercritical antisolvent precipitation of TiO2 with tailored anatase/rutile composition for applications in redox catalysis and Ppotocatalysis

TiO2 with tailored anatase/rutile composition has been prepared from the supercritical antisolvent (SAS) precipitation of a range of titanium alkoxides. The calcination of the SAS TiO2 was monitored by in situ powder X-ray diffraction to determine the optimal calcination conditions for the formation of a mixed anatse/rutile phase TiO2. The SAS precipitated material calcined at 450 °C produced a predominantly anatase support while calcination at 750 °C resulted in a 90 wt% anatase and 10 wt% rutile TiO2. 5 wt% AuPd was added to the SAS TiO2 using an impregnation technique, with exceptional dispersion of the metals being observed by transmission electron microscopy. Mean metal particle sizes were determined to be below 1 nm for both anatase and anatase/rutile SAS TiO2 materials. These catalysts were found to be highly active for the selective oxidation of benzyl alcohol and the direct synthesis of hydrogen peroxide. In addition the anatase/rutile SAS TiO2 was found to have comparable activity to commercial anatase/rutile mixed phase TiO2 for the photocatalytic splitting of water for hydrogen production

Predictors of outcome in fungal keratitis

PURPOSE: To analyse predictors of clinical outcome in fungal keratitis. METHODS: Data was collected during a prospective, randomized, controlled, double-masked clinical trial of treatment for fungal keratitis. Clinical features at presentation and demographics were collected at the enrolment visit for all patients. Pre-specified clinical outcomes included 3-month visual acuity and infiltrate/scar size, time to re-epithelialization, and corneal perforation. A separate multivariable model with each outcome as the dependent variable included all predictor variables. RESULTS: Predictors for worse 3-month visual acuity include older age (P=0.024), worse presentation visual acuity (P<0.001), larger infiltrate size at presentation (P<0.001), and pigmented ulcer (P=0.030). Larger infiltrate size at presentation was a significant predictor of worse 3-month infiltrate/scar size (P<0.001). Larger epithelial defect size was a significant predictor of perforation (P=0.0013). Predictors of longer time to re-epithelialization include infiltrate size at presentation (P<0.001) and older age (P=0.025). CONCLUSION: Ulcer severity at presentation is highly predictive of worse outcomes. Presentation of clinical characteristics such as baseline acuity and infiltrate scar can provide important information to clinicians about prognosis, and may help guide management and treatment decisions. Prevention of corneal ulcer remains important, as it is difficult to change the course of the ulcer once it has begun