Ni Catalysts Supported Over TiO2, SiO2 and ZrO2 for the Steam Reforming of Glycerol

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Ni Catalysts Supported Over TiO2, SiO2 and ZrO2 for the Steam Reforming of Glycerol

Ni-based catalysts supported on TiO2, ZrO2 and SiO2 (in the form of mesoporous Santa Barbara Amorphous 15 (SBA-15) and amorphous dense nanoparticles), were employed in the steam reforming of glycerol. Each sample was prepared by liquid phase synthesis of the support followed by impregnation with the active phase and calcination at 8008C or by direct synthesis through flame pyrolysis. Many techniques have been used to assess the physical chemical properties of both the fresh and spent catalysts, such as atomic absorption, N2 adsorption/desorption, XRD, SEM, TEM, temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), Micro-Raman and FTIR spectroscopy. The samples showed different textural, structural and morphological properties,as well as different reducibility and thermal resistance depending on the preparation method and support. Some of these properties were tightly bound to catalyst performance, in terms of H2 productivity and stability towards coking and sintering. A key parameter was the metal\u2013support interaction, which strongly depended on the preparation procedure. In particular, the stronger the interaction, the more stable the metallic Ni clusters, which in turn lead to a higher catalytic activity and stability. Surface acidity was also taken into account, in which the nature of the acid sites was differentiated (silanols, titanols or Lewis acid sites). The characterisation of the spent catalysts also allowed us to interpret the deactivation process. The formation of multi-walled nanotubes was observed for every sample, though it was only in some cases that this led to severe deactivatio

Effect of the support on Ni catalytic performance in glycerol steam reforming

In the last years, the use of hydrogen as new energy vector has been widely encouraged, because it is clean and carbon-free [1]. Nevertheless, an effective solution of environmental problems such as the greenhouse effect and the global warming, as well as the decrease of the dependence on fossil fuels, requires the use of renewable sources. In this context glycerol, the main by-product in biodiesel production, has emerged as a promising source of hydrogen, because of its high hydrogen content and renewability, safeness and non toxicity [2]. Several catalysts have been proposed for glycerol steam reforming. In this work we report the catalytic performances of Ni-based catalysts at two different reaction temperatures. Moreover, the effect of the support (i. e. TiO2, SBA-15 and ZrO2) on the selectivity to hydrogen was studied. TiO2 and ZrO2 were synthesized by a conventional precipitation method [3], whereas SBA15 was prepared through a template synthesis [4]. Catalysts were prepared by incipient wetness impregnation of the supports with an aqueous solution of the Ni precursor in order to obtain a 10 wt% Ni loading and they were finally calcined. The physico-chemical properties of the catalysts were determined by nitrogen physisorption analysis (BET), temperature programmed reduction (TPR) and high resolution transmission electron microscopy (HR-TEM). The activity tests were carried out in a fixed bed tubular quartz reactor at atmospheric pressure at two different temperatures (500°C and 650°C), after reduction of the samples in H2 flow for 1 hour at either 500 or 700°C respectively. A water/glycerol solution was fed (10 wt% solution of glycerol in water) at the constant flow rate of 0.06 mL/min. Data were collected up to 20 hours on each sample. The Ni/TiO2 sample exhibits negligible activity at 650°C because of the collapse of the support. Concerning Ni/SBA-15, our results indicate the insufficient hydrothermal resistance of the support, which leads to the progressive deactivation of the catalyst. However this support is able to stabilize the active phase in a rather efficient way, thus preventing Ni sintering. Ni/ZrO2 exhibits the best performances: a stable glycerol conversion of ~72% and a hydrogen yield of ~65% were obtained. This is due to the almost full preservation of the structure of the zirconia support even after 20 h in the SR conditions; moreover, also the dispersion of the Ni active phase remainedunchanged. The different behaviour of the three catalysts can be then ascribed (i) to the chemical, thermal and mechanical resistance of the support in the reaction conditions and (ii) to the intensity of the interactions between the support and the active phase, which affects in particular the stability of the Ni nanoparticles. Our results highlight the importance of the nature of the support, which plays a key role in designing the catalytic performance

“Silica and zirconia supported catalysts for the low-temperature ethanol steam reforming"

Ethanol steam reforming has been investigated in the low temperature range, focusing not only on H2pro-ductivity, but also on catalyst stability, very critical parameters under such conditions. Different supports(SiO2and ZrO2), active phases (Ni, Co, Cu) and reaction temperature (300–500◦C) have been employed.Ni confirmed the best performing active phase to promote ethanol decomposition and reforming alreadyat low reaction temperature. However, stability towards coking remains a key problem. The supportplays a key role from this point of view. Indeed, the stabilization of the active phase in very dispersedform allowed to reach stable catalyst performance with time-on-stream. SiO2, thanks to no Lewis acidityand sufficiently strong metal–support interaction, demonstrated an interesting support for Ni under theselected operating condition

Ni/TiO2 for ethanol steam reforming: which is the best synthetic approach?

The performance of Ni/TiO2 catalysts in ethanol steam reforming (SR) was considered in this study; in particular, the effects of both the methodology of Ni introduction and calcination temperature were deeply investigated. Activity strongly depends on the physico-chemical properties of the catalyst, that greatly change according to the synthetic approach. Introduction Ethanol SR for a cleaner hydrogen production is an attracting topic for researchers and the design of a highly active and selective catalyst is a key point for the fulfilment of this process on industrial scale. Nickel is known to be both active and selective in the SR reactions, but also the support plays an essential role. The aim of this work is the investigation of the effect of the synthetic parameters on the physico-chemical properties of the sample and on its catalytic performance. Experimental TiO2 support was prepared by a conventional precipitation method . Ni (10 wt%) was added to the support by means of incipient wetness impregnation with an aqueous solution of the metallic precursor, either before (NiC) or after (CNi) the calcination of the support. Samples were calcined at 500 \ub0C (NiC500 and CNiC500) or at 800 \ub0C (NiC800). The samples were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), high-resolution transmission electron microscopy (HR-TEM) and N2 physisorption. Activity tests were performed after reduction of the catalysts in H2 flow for 1h at 500 \ub0C for samples calcined at 500 \ub0C, at 800 \ub0C for NiC800. The activity tests were carried out at atmospheric pressure by feeding a 3:1 (mol/mol) H2O:CH3CH2OH mixture at 500 \ub0C. Results and discussion The characterization measurements we carried out reveal marked differences among the samples, in particular for what concerns the interactions between the active phase and the support and, as a consequence, Ni availability to the reaction. XRD pattern on NiC500 before the reduction reveals only nanocrystalline anatase. This suggests that all nickel species have been incorporated in the anatase lattice1, , thus making Ni unavailable for the reaction. In fact, this sample is almost completely inactive in ethanol SR. Ni incorporation in TiO2 is due to Ni impregnation before the calcination of the support. When Ni is added to the calcined support (CNiC500), no incorporation in the anatase lattice is detected. This sample is more active than NiC500 (EtOH conversion: 82%; H2 productivity: 0.21 mol min-1 kgcat-1), but it is not stable. The calcination treatment at high temperature (NiC800) stabilizes the active phase by strengthening the interactions of Ni species with the support (SMSI), with the formation of an ilmenite-type structure (NiTiO3) in which nickel is still reducible to Ni0. The catalytic performance of this catalyst is satisfactory, with an ethanol conversion of 99% and a H2 productivity of 0.84 mol min-1 kgcat-1. Conclusions The ability of the support to increase Ni availability to the reaction and to stabilize the active phase is of primary importance to achieve both high ethanol conversion and H2 productivity. The results indicate that TiO2-supported Ni systems are very sensitive to the synthetic procedure. The best catalytic performances are obtained by calcining at the highest temperature