RESUMEN
Ferrierites and their delaminated (ITQ-6) and silica intercalated (ITQ-36) forms, with the intended molar Si/Al ratios of zeolite layers of 30 and 50, were synthesized and tested as catalysts of methanol to dimethyl ether (DME) as well as ethanol to diethyl ether (DEE) and ethylene dehydration. It was shown that increased content of acid sites, especially of Brønsted type, resulted in more active catalysts of alcohol dehydration. Brønsted acid sites dominate in ferrierites and their delaminated forms (ITQ-6). Contribution of the Lewis type of acid sites increased in silica pillared ferrierites (ITQ-36) possibly by deposition of aluminium species on the surface of amorphous silica. Conversion of methanol to DME was not limited by internal diffusion of reactants in narrow pores of ferrierite. Such limitation was observed for synthesis of larger DEE molecules over ferrierites. The ITQ-6 catalysts with the opened interlayer structure presented better efficiency in ethanol to DEE conversion due to overcoming these diffusional restrictions. Moreover, selectivity to DEE over ITQ-6 was higher than in the presence of three-dimensional ferrierite.
RESUMEN
In this paper, we describe the role of anatase and rutile crystal phases on diphenyl sulphide (Ph2S) catalytic and photocatalytic oxidation. The highly selective and efficient synthesis of diphenyl sulfoxide (Ph2SO) and diphenyl sulfone (Ph2SO2) at titanium dioxide was demonstrated. Ph2S oxidation in the presence of hydrogen peroxide at anatase-TiO2 can take place both as a catalytic and photocatalytic reaction, while at rutile-TiO2 only photocatalytic oxidation is possible. The reaction at anatase leads mainly to Ph2SO2, whereas, in the presence of rutile a complete conversion to Ph2SO is achieved after only 15 min (nearly 100% selectivity). Studies on the mechanistic details revealed a dual role of H2O2. It acts as a substrate in the reaction catalysed only by anatase, but it also plays a key role in alternative photocatalytic oxidation pathways. The presented study shows the applicability of photocatalysis in efficient and selective sulfoxide and sulfone production.
RESUMEN
Titanium-silicon ferrierites with different Si/Ti ratios and their delaminated forms were modified with copper by ion-exchange. The obtained samples were characterized with respect to their chemical composition (ICP-OES), structure (XRD), texture (N2 sorption), morphology (SEM), form and aggregation of titanium and copper species (UV-vis-DRS), reducibility of deposited copper species (H2-TPR) and surface acidity (NH3-TPD). The porous structure of the zeolitic samples strongly influenced the form and aggregation of deposited copper species. In the case of the three dimensional microporous structure of ferrierites (Ti-FER), copper was deposited mainly in the form of aggregated copper oxide species, in contrast to the open micro- and mesoporous structure of delaminated ferrierites (Ti-ITQ-6), where mainly copper in the form of monomeric cations was identified. It was shown that monomeric copper cations are more catalytically active in NO to NO2 oxidation than aggregated copper oxide species and, therefore, for the low-temperature conversion of nitrogen oxides the fast SCR reaction pathway is more effective for delaminated ferrierites modified with copper (Cu-Ti-ITQ-6) than for microporous three dimensional ferrierite catalysts (Cu-Ti-FER).
RESUMEN
Ferrierites and their delaminated forms (ITQ-6), containing aluminum or titanium in the zeolite framework, were synthetized and modified with copper by an ion-exchange method. The obtained samples were characterized with respect to their chemical composition (ICP-OES), structure (XRD, UV-Vis DRS), textural parameters (N2-sorption), surface acidity (NH3-TPD), form and reducibility of deposited copper species (UV-Vis DRS and H2-TPR). Ferrierites and delaminated ITQ-6 zeolites modified with copper were studied as catalysts for the selective catalytic oxidation of ammonia to dinitrogen (NH3-SCO). It was shown that aggregated copper oxide species, which were preferentially formed on Ti-zeolites, were catalytically active in direct low-temperature ammonia oxidation to NO, while copper introduced into Al-zeolites was present mainly in the form of monomeric copper cations catalytically active in selective reduction of NO by ammonia to dinitrogen. It was postulated that ammonia oxidation in the presence of the studied catalysts proceeds according to the internal-selective catalytic reduction mechanism (i-SCR) and therefore the suitable ratio between aggregated copper oxide species and monomeric copper cations is necessary to obtain active and selective catalysts for the NH3-SCO process. Cu/Al-ITQ-6 presented the best catalytic properties possibly due to the most optimal ratio of these copper species.
