Selectivity control in Pt-catalyzed cinnamaldehyde hydrogenation

Chemoselectivity is a cornerstone of catalysis, permitting the targeted modification of specific functional groups within complex starting materials. Here we elucidate key structural and electronic factors controlling the liquid phase hydrogenation of cinnamaldehyde and related benzylic aldehydes over Pt nanoparticles. Mechanistic insight from kinetic mapping reveals cinnamaldehyde hydrogenation is structure-insensitive over metallic platinum, proceeding with a common Turnover Frequency independent of precursor, particle size or support architecture. In contrast, selectivity to the desired cinnamyl alcohol product is highly structure sensitive, with large nanoparticles and high hydrogen pressures favoring C=O over C=C hydrogenation, attributed to molecular surface crowding and suppression of sterically-demanding adsorption modes. In situ vibrational spectroscopies highlight the role of support polarity in enhancing C=O hydrogenation (through cinnamaldehyde reorientation), a general phenomenon extending to alkyl-substituted benzaldehydes. Tuning nanoparticle size and support polarity affords a flexible means to control the chemoselective hydrogenation of aromatic aldehydes.

Solid biofuel production by mechanical pre-treatment of brewers' spent grain

The brewing industry produces large amounts of by-products and wastes like brewers' spent grain (BSG). In Germany, each year approximately 2.1 million tonnes of BSG are generated. During the last years conventional routes of BSG utilization face a remarkable change, such as the decline in the demand as animal feed. Due to its high content of organic matter energetic utilization may create an additional economic value for breweries. Furthermore, in the recent past breweries tend to shift their energy supply towards more sustainable concepts. Although, a decent number of research projects were carried out already, still no mature strategy is available. However, one possible solution can be the mechanical pretreatment of BSG. This step allows optimized energy utilization by the fractionation of BSG. Due to the transfer of digestible components, such as protein, to the liquid phase, the solid phase will largely consist of combustible components. That represents an opportunity to produce a solid biofuel with lower fuelnitrogen content compared to only thermal dried BSG. Therefore, two main purposes for the mechanical pre-treatment were determined, (1) to reduce the moisture content to at least 60 % (w/w) and (2) to diminish the protein content of the solid phase by 30 %. Moreover, the combustion trials should demonstrate whether stable processes and flue gas emissions within the legal limits in Germany are feasible. The results of the mechanical pre-treatment trials showed that a decrease of the moisture and protein content has been achieved. With regard to the combustion trials inconsistent outcomes were found. On the one hand a stable combustion was realized. On the other hand the legal emission levels of NOx (500 mgm -3) and dust (50 mgm-3) could not be kept during all trials. The further research steps will focus on the optimization of the air/fuel ratio by reducing the primary and secondary air conditions. Copyright © 2014,AIDIC Servizi S.r.l.

Highly selective hydrogenation of furfural over supported Pt nanoparticles under mild conditions

The selective liquid phase hydrogenation of furfural to furfuryl alcohol over Pt nanoparticles supported on SiO2, ZnO, γ-Al2O3, CeO2 is reported under extremely mild conditions. Ambient hydrogen pressure, and temperatures as low as 50 °C are shown sufficient to drive furfural hydrogenation with high conversion and >99% selectivity to furfuryl alcohol. Strong support and solvent dependencies are observed, with methanol and n-butanol proving excellent solvents for promoting high furfuryl alcohol yields over uniformly dispersed 4 nm Pt nanoparticles over MgO, CeO2 and γ-Al2O3. In contrast, non-polar solvents conferred poor furfural conversion, while ethanol favored acetal by-product formation. Furfural selective hydrogenation can be tuned through controlling the oxide support, reaction solvent and temperature.

Self-assembled SnO2 micro- and nanosphere-based gas sensor thick films from an alkoxide-derived high purity aqueous colloid precursor

Tin oxide is considered to be one of the most promising semiconductor oxide materials for use as a gas sensor. However, a simple route for the controllable build-up of nanostructured, sufficiently pure and hierarchical SnO2 structures for gas sensor applications is still a challenge. In the current work, an aqueous SnO2 nanoparticulate precursor sol, which is free of organic contaminants and sorbed ions and is fully stable over time, was prepared in a highly reproducible manner from an alkoxide Sn(OR)4 just by mixing it with a large excess of pure neutral water. The precursor is formed as a separate liquid phase. The structure and purity of the precursor is revealed using XRD, SAXS, EXAFS, HRTEM imaging, FTIR, and XRF analysis. An unconventional approach for the estimation of the particle size based on the quantification of the Sn-Sn contacts in the structure was developed using EXAFS spectroscopy and verified using HRTEM. To construct sensors with a hierarchical 3D structure, we employed an unusual emulsification technique not involving any additives or surfactants, using simply the extraction of the liquid phase, water, with the help of dry butanol under ambient conditions. The originally generated crystalline but yet highly reactive nanoparticles form relatively uniform spheres through self-assembly and solidify instantly. The spheres floating in butanol were left to deposit on the surface of quartz plates bearing sputtered gold electrodes, producing ready-for-use gas sensors in the form of ca. 50 μm thick sphere-based-films. The films were dried for 24 h and calcined at 300°C in air before use. The gas sensitivity of the structures was tested in the temperature range of 150-400°C. The materials showed a very quickly emerging and reversible (20-30 times) increase in electrical conductivity as a response to exposure to air containing 100 ppm of H2 or CO and short (10 s) recovery times when the gas flow was stopped.

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.

Effects of solid poly (ethylene glycols) addition to the solutions of aniline or N,N-dimethylaniline with water:experimental measurements and modelling

In this work, the liquid-liquid and solid-liquid phase behaviour of ten aqueous pseudo-binary and three binary systems containing polyethylene glycol (PEG) 2050, polyethylene glycol 35000, aniline, N,N-dimethylaniline and water, in the temperature range 298.15-350.15 K and at ambient pressure of 0.1 MPa, was studied. The obtained temperature-composition phase diagrams showed that the only functional co-solvent was PEG2050 for aniline in water, while PEG35000 even showed a clear anti-solvent effect in the N,N-dimethylaniline aqueous system. The experimental solid-liquid equilibria (SLE) data have been correlated by the non-random two-liquid (NRTL) model, and the correlation results are in accordance with the experimental results.