Scientific Papers in SCI

There are multiple factors that influence the catalyst performance in the reaction of formic acid dehydrogena-tion: the nature of catalyst and/or support, the used solvent and reaction variables such as temperature, time, formic acid concentration, presence/absence of formates and pH of the solution. This work evaluates a series of important parameters like the influence of the pH by itself, the influence of the nature of used alkali agents and the effect of direct formate addition as reactive on hydrogen production via formic acid dehydrogenation over a commercially available catalyst. The catalytic performance appears to depend on the ionic radius of the cations of the used base which reflects consequently on the hydrogen selectivity. The best base to be used must have lower hydrated cationic radii and a starting pH around 4 to achieve important hydrogen selectivity for medium term formic acid conversion.

BACKGROUND: Phenol and its derivatives are considered toxic compounds, even at low concentrations. Their accumulation in water effluents has become a serious problem that could be resolved by using zinc oxide (ZnO)-based photocatalysts.RESULTS: ZnO nanoparticles were synthesized through the precipitation method, using zinc nitrate and sodium carbonate as reagents. The as-synthesized powder was calcined for 4 h at 500 degrees C (2 degrees C min(-1)). X-Ray diffraction analysis confirmed a hexag-onal crystalline phase (wurtzite) with an average crystallite size of 38 nm. The Kubelka-Munk method was used to determine a band gap of 3.27 eV through UV-Vis diffuse reflectance spectrum and a Brunauer-Emmett-Teller (BET) specific area of 12 m(2) g(-1) was obtained from N2 adsorption analysis. The photocatalytic activity of ZnO was evaluated under visible light (300 W) lamp, with 1 mg mL(-1) of photocatalyst and using phenol solutions at different concentrations of 5,10, 25, and 50 ppm; the obtained degradation percentages were 98%, 97%, 94%, and 71%, respectively. Three cycles were performed with the ZnO used in the reactions with phenol at 5 and 50 ppm, decreasing the degraded percentages to 87% and 65%, respectively. The generation of hydroxyl radicals was estimated for the ZnO and ZnO samples after three cycles by means of fluorescence spectroscopy analy-sis. It was observed that the first-used ZnO material generated a significant amount of hydroxyl radicals.CONCLUSION: When compared to ZnO after three cycles of reaction, the amount of generated hydroxyl radicals decreased. It was observed that the higher the amount of phenol, the lower the generation of hydroxyl radicals after reuse; this was probably due to the presence of some adsorbed by-products of the photocatalytic reaction on the surface of ZnO, as the FTIR spectrum of the post-reaction sample showed.

Rhodium-catalysed hydroformylation, effective tool in bulk and fine-chemical synthesis, predominantly uses soluble metal complexes. For that reason, the metal leaching and the catalyst recycling are still the major drawbacks of this process. Single-atom catalysts have emerged as a powerful tool to combine the advantages of both homogeneous and heterogeneous catalysts. Since using an appropriate support material is key to create stable, finely dispersed, single-atom catalysts, here we show that Rh atoms anchored on graphitic carbon nitride are robust catalysts for the hydroformylation reaction of styrene.

The sintering behaviour of a pyrophyllite clay has been investigated. The mineralogical composition by X-ray diffraction (XRD) of this sample was -35 wt.% pyrophyllite, -25 wt.% sericite/illite, -15 wt.% kaolinite and -20 wt.% quartz. The chemical composition was consistent with these results, with a total flux content of 4.18 wt.%. Prismatic bars were prepared by dry pressing using this sample and fired in the range 800-1500 degrees C with 0.5-5 h of soaking times. Sintering diagrams were obtained using the results of linear firing shrinkage, water absorption capacity, bulk density and apparent porosity determined in the ceramic bodies as a function of firing temperatures. It was found a trend of slight variations of bulk density values firing in the range 1000-1150 degrees C, with marked decreases of these values for these bodies fired at 1200 degrees C and 1300 degrees C. The temperature of maximum bulk density was determined as -1200 degrees C and the vitrification temperature was -1300 degrees C where the apparent porosity becomes almost zero. The vitrification process of the pyrophyllite clay sample was investigated using a method previously described in the literature, which considered an Arrhenius approach under isothermal conditions and a first order kinetic. It was determined an activation energy (Ea) of -45 kJ/mol with a linear correlation coefficient of 0.998. The relative rates of vitrification were calculated. It was found that the contribution of vitrification due to the heating was relatively small compared to the vitrification during soaking. Mullite and quartz are forming the ceramic bodies besides a vitreous or glassy phase. The thermally treated pyrophyllite clay showed a dense network of rod-shaped and elongated needle-like crystals, being characteristic features of mullite as a dense felt. The vitrification rate equation, as deduced in this study by first time, can be a useful tool to estimate the optimum firing conditions of the pyrophyllite clays applied as ceramic raw materials.