D. Mucha

Catalytic performance of the dodecatungstophosphoric acid on different supports

Abstract Varying amounts of tungstophosphoric acid (HPW) have been supported on Y-type zeolite and silica using the incipient wetness method. The catalytic activity of the catalysts was studied in the vapor-phase dehydration of ethanol. The reaction was carried out in a conventional flow-type reactor under atmospheric pressure at temperatures changing from 398 to 773xa0K. Unexpectedly, deposition of heteropolyacid on zeolite HY with the loadings decreasing from 46.8 to 0.00016xa0wt.% results in catalysts characterized by the same catalytic activity indicating that the catalytic behaviour is determined by few very active sites, composed of Keggin anions and lacunary Keggin anions located in the supercages opened at the surface, which has a honeycomb structure. Contrary to the series of HPW/Y catalysts, HPW supported on SiO 2 shows decreasing catalytic activity when its concentration lowers, the monolayer being catalytically inactive in acid–base reactions.

Physicochemical and electrochemical properties of the carbon materials containing nitrogen and cobalt derived from acetonitrile and Co–Al layered double hydroxides

Two sets of the carbon materials containing nitrogen and cobalt were prepared by simultaneous carbonization of CH3CN and decomposition of Co–Al layered double hydroxides (LDHs) (of Co/Al atomic ratios equal to 2 or 3) at 600, 700 and 800xa0°C followed by treatment with HCl. The physicochemical features of the samples were characterized by means of XRD, TG, EA, XPS, XRF, FT-IR, SEM, Raman spectroscopy and nitrogen sorption. All of the composites were active in oxygen reduction reaction (ORR) in alkaline medium. Their ORR behaviour was determined by the contribution of structural defects and N-doping in graphitic lattice. The beneficial effect of metallic cobalt encapsulated inside the N-CNTs on the ORR performance was also taken into consideration. The studies showed that the likelihood of the existence of Co–N–C species and their participation in ORR seemed to be suppressed by the formation of CoAl2O4. The samples prepared at 600 and 700xa0°C appeared to be more active in ORR than that obtained at 800xa0°C. The number of electrons involved in ORR (2.89, 2.82 and 2.77) decreased with increasing synthesis temperature for the samples prepared with LDHs of Co/Alu2009=u20092 as a consequence of lowering concentration of nitrogen (3.2, 2.4 and 1.5xa0wt%), in particular diminishing contribution of pyridinic nitrogen, and decreasing exposure of graphitic edges (ID1/IGu2009~u20092.6, 2.0 and 1.0). The ORR performance of the samples prepared with LDHs of Co/Alu2009=u20093 is comparable to that of the corresponding samples prepared with LDHs of Co/Alu2009=u20092.