Heterogeneously Catalyzed Continuous-Flow Hydrogenation Using Segmented Flow in Capillary Columns

Segmented flow in standard GC capillary columns, with a heterogeneous Pd catalyst on the walls, gave rapid information about catalytic processes in them. The residence time and conversion was monitored visually, greatly simplifying bench-scale optimization. Examples show the benefits of the elimination of pore diffusion and axial dispersion. Further, we demonstrated how to quickly identify deactivating species in multistep synthesis without intermediate workup

Tail gas catalyzed N2O decomposition over Fe-beta zeolite. On the promoting role of framework connected AlO6 sites in the vicinity of Fe by controlled dealumination during exchange

A novel route to prepare highly active and stable N2O decomposition catalysts is presented, based on Fe-exchanged beta zeolite. The procedure consists of liquid phase Fe(III) exchange at low pH. By varying the pH systematically from 3.5 to 0, using nitric acid during each Fe(III)-exchange procedure, the degree of dealumination was controlled, verified by ICP and NMR. Dealumination changes the presence of neighbouring octahedral Al sites of the Fe sites, improving the performance for this reaction. The so-obtained catalysts exhibit a remarkable enhancement in activity, for an optimal pH of 1. Further optimization by increasing the Fe content is possible. The optimal formulation showed good conversion levels, comparable to a benchmark Fe-ferrierite catalyst. The catalyst stability under tail gas conditions containing NO, O2 and H2O was excellent, without any appreciable activity decay during 70 h time on stream. Based on characterisation and data analysis from ICP, single pulse excitation NMR, MQ MAS NMR, N2 physisorption, TPR(H2) analysis and apparent activation energies, the improved catalytic performance is attributed to an increased concentration of active sites. Temperature programmed reduction experiments reveal significant changes in the Fe(III) reducibility pattern with the presence of two reduction peaks; tentatively attributed to the interaction of the Fe-oxo species with electron withdrawing extraframework AlO6 species, causing a delayed reduction. A low-temperature peak is attributed to Fe-species exchanged on zeolitic AlO4 sites, which are partially charged by the presence of the neighbouring extraframework AlO6 sites. Improved mass transport phenomena due to acid leaching is ruled out. The increased activity is rationalized by an active site model, whose concentration increases by selectively washing out the distorted extraframework AlO6 species under acidic (optimal) conditions, liberating active Fe species

The influence of NO x on soot oxidation rate: molten salt versus platinum

Abstract A systematic study was carried out to assess the influence of simulated diesel exhaust on the activity of molten salt, Cs 2 SO 4 ·V 2 O 5 , supported on ceramic foam and Pt/␥-alumina catalysts in the oxidation of diesel soot. Gas compositions containing O 2 , NO x , CO, C 3 H 6 , and SO 2 were used. The activity of molten salt catalyst, an active catalyst for the oxidation of soot with O 2 , is slightly affected by the gas component due to NO 2 already present in NO x . In contrast, the presence of NO x , significantly increases the soot oxidation rate with platinum catalyst. These changes were due to the catalytic oxidation of NO to NO 2 with platinum, followed by soot oxidation with NO 2 . Three configurations are compared, viz. a fixed bed containing a physical mixture of Pt catalyst and soot, Pt catalyst upstream of a fixed bed containing soot, and Pt catalyst upstream of soot loaded on ceramic foam supported molten salt. The reaction cycle of oxidation of NO, followed by soot oxidation with the NO 2 produced, was observed only in a physical mixture of platinum catalyst and soot

Gas phase stabiliser-free production of hydrogen peroxide using supported gold-palladium catalysts

Hydrogen peroxide synthesis from hydrogen and oxygen in the gas phase is postulated to be a key reaction step in the gas phase epoxidation of propene using gold–titanium silicate catalysts. During this process H2O2 is consumed in a secondary step to oxidise an organic molecule so is typically not observed as a reaction product. We demonstrate that using AuPd nanoparticles, which are known to have high H2O2 synthesis rates in the liquid phase, it is possible to not only oxidise organic molecules in the gas phase but to detect H2O2 for the first time as a reaction product in both a fixed bed reactor and a pulsed Temporal Analysis of Products (TAP) reactor without stabilisers present in the gas feed. This observation opens up possibility of synthesising H2O2 directly using a gas phase reaction

The direct synthesis of hydrogen peroxide using a combination of a hydrophobic solvent and water

The direct synthesis of hydrogen peroxide (H2O2) has been studied using a solvent system comprising a hydrophobic alcohol (decan-1-ol) and water. It is demonstrated that, with the optimum combination of solvent and catalyst the contribution of H2O2 degradation pathways can be minimised to achieve industrially acceptable H2O2 concentrations under moderate conditions. This is achieved through the use of a catalyst that is retained by the organic component and the extraction of synthesised H2O2 into the aqueous phase, consequently limiting contact between the synthesised H2O2, catalyst and reactant gases, resulting in an improved selectivity towards H2O2. Investigation of the reaction parameters provides an insight into the proposed solvent system, and optimised conditions to produce H2O2 from molecular H2 and O2 have been identified. Through this optimisation H2O2 concentrations up to 1.9 wt% have been achieved via sequential gas replacement experiments