N-heterocyclic carbene iron complexes catalyze the ring-opening polymerization of lactide

Poly(lactic acid), PLA, which holds great promises as a biodegradable substitute of fossil resource-derived polyolefins, is industrially produced by the ring-opening polymerization of lactide using a potentially harmful tin catalyst....

Direct Electrochemical Reduction of Bicarbonate to Formate Using Tin Catalyst

Nowadays, the self-accelerating increase in global temperatures strengthens the idea that the cutting of CO2 emissions will not be enough to avoid climate change, thus CO2 from the atmosphere must be removed. This gas can be easily trapped by converting it to bicarbonate using hydroxide solutions. However, bicarbonate must be converted into a more valuable product to make this technology profitable. Several studies show great efficiency when reducing bicarbonate solutions saturated with pure CO2 gas to formate. However, those approaches don’t have a real application and our objective was to obtain similar results without pure CO2 saturation. The method consists of electroreduction of the bicarbonate solution using bulk tin (Sn) as catalysts. Tin is a relatively cheap material that, according to previous studies performed in saturated bicarbonate solutions, shows a great selectivity towards formate. The 1H NMR analysis of bicarbonate solutions after electroreduction show that, without pure CO2 gas, the faradic efficiency is around 18% but almost 50% for saturated ones. The formate obtained could be used to power formate/formic acid fuel cells obtaining a battery-like system, with greater energy density than common lithium batteries, but electroreduction efficiency needs to be improved to make them competitive.

Synthesis and properties of Pt/TiN catalyst for low-temperature air purification from carbon monoxide

Catalysts of carbon monoxide oxidation were synthesized by deposition of platinum on titanium nitride (TiN). Two substrates with an average particle size of 18 and 36 nm were obtained by hydrogen reduction of titanium tetrachloride in a stream of microwave plasma of nitrogen. The surface of the catalysts was studied by X-ray photoelectron spectroscopy (XPS). The data obtained by us in the present work indicate the presence of oxynitride as a transition layer between nitride and oxide. It was found that the CO oxidation rate on the 9–15 wt. % Pt loaded TiN catalysts is 120 times higher than that on the platinum black with a specific surface of 30 m2g–1. Increase in the reaction rate of CO oxidation on Pt/TiN catalysts as compared to platinum black can be associated with both an increase in the concentration of CO molecules adsorbed and a decrease in the activation energy of the reaction. Catalysts are promising for use in catalytic air purification systems.

Highly efficient and durable III–V semiconductor-catalyst photocathodes via a transparent protection layer

Integration of crystalline Ni5P4–TiN catalyst-protection layer on buried junction n+p-GaInP2.

Bimetallic iron–tin catalyst for N2 to NH3 and a silyldiazenido model intermediate

A new tin-supported iron complex catalyzes N2 fixation. The role of this heavy main group element in the catalysis is evaluated.

NMR Analysis of Poly(Lactic Acid) via Statistical Models

The physical properties of poly(lactic acid) (PLA) are influenced by its stereoregularity and stereosequence distribution, and its polymer stereochemistry can be effectively studied by NMR spectroscopy. In previously published NMR studies of PLA tacticity, the NMR data were fitted to pair-addition Bernoullian models. In this work, we prepared several PLA samples with a tin catalyst at different L,L-lactide and D,D-lactide ratios. Upon analysis of the tetrad intensities with the pair-addition Bernoullian model, we found substantial deviations between observed and calculated intensities due to the presence of transesterification and racemization during the polymerization processes. We formulated a two-state (pair-addition Bernoullian and single-addition Bernoullian) model, and it gave a better fit to the observed data. The use of the two-state model provides a quantitative measure of the extent of transesterification and racemization, and potentially yields useful information on the polymerization mechanism.

Morphology and composition of silica nanowires synthesized on indium and tin catalysts

Silicon nanowires were synthesized by electron beam plasmaenhanced chemical vapor deposition. The synthesis was carried out using indium and tin catalyst with an average particle size of 100 and 660 nm, respectively, in the temperature range 100-270 °C for indium and 200-335 °C for tin. The minimum (optimum) temperature was found at which an oriented array of microropes was formed. This temperature was 200 °C for indium and 335 °C for tin. In addition, it was found that the formation of individual microropes on the tin catalyst occurred at a temperature lower than the eutectic temperature (232 °C). For indium, this effect was not observed. The silica nanowires synthesized on both catalysts consist of SiOx with x ranging from 1.9 to 2 for all temperatures.