Flame pyrolysis synthesis of mixed oxides for glycerol steam reforming

Flame spray pyrolysis was used to produce nanosized Ni-based catalysts starting from different mixed oxides. LaNiO3 and CeNiO3 were used as base materials and the formulation was varied by mixing them or incorporating variable amounts of ZrO2 or SrO during the synthesis. The catalysts were tested for the steam reforming of glycerol. One of the key problems for this application is the resistance to deactivation by sintering and coking, which may be increased by (1) improving Ni dispersion through the production of a Ni-La or Ni-Ce mixed oxide precursor, and then reduced; (2) using an oxide as ZrO2, which established a strong interaction with Ni and possesses high thermal resistance; (3) decreasing the surface acidity of ZrO2 through a basic promoter/support, such as La2O3; and (4) adding a promoter/support with very high oxygen mobility such as CeO2. A further key feature is the use of a high temperature synthesis, such as flame spray pyrolysis, to improve the overall thermal resistance of the oxides. These strategies proved effective to obtain active and stable catalysts at least for 20 h on stream with very limited coke formation

Discovering indium as hydrogen production booster for a Cu/SiO2 catalyst in steam reforming of methanol

We report on the use of In as an effective H2 production promoter in a Cu/SiO2 catalyst for the steam reforming of methanol. To date, In promotion has been limited to noble metals because of its tendency to “bury” other metals thus compromising the catalytic activity. Here, we prepared a silica-supported Cu-In catalyst via a urea-assisted co-precipitation method that showed a higher H2 productivity compared to the monometallic catalyst and a remarkable H2/CO2 molar ratio of almost 3 at 220 °C. Through XPS, XRPD and HRTEM-EDX along with H2- and CO-TPR, H2O-TPD, and N2O titrations, supported by computational modeling, we attributed such superior performances to an easier H2O activation due to improved electronic properties of the Cu phase, that is, its lower oxidation state via electron density transfer from the InOx buffer phase as a 1D “necklace” structures crucially mediating the interaction of small Cu nanoparticles (2.6 nm) and silica

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

Photocatalytic degradation of acetone in gas-phase: comparison between nano and micro-sized TiO2

Volatile Organic Compounds (VOCs) are widely used in industrial processes and for domestic activities, so generating water and air pollution. Well-known in-door sources of VOCs include cigarette smoke, building materials, paints, lacquers, glues and cleaning products [1]. In particular, the use of paints in industrial processes is responsible for the widespread utilization of organics solvents, such as acetone. Acetone (CH3COCH3) is a common chemical used extensively in a variety of in-dustrial and domestic applications. Therefore, we chose it as a model contaminant. Photocatalytic oxidation of acetone is based on the following overall reaction: CH3COCH3 + 4O2 \u2192 3CO2 + 3H2O The reaction occurs through radical mechanism car-ried out by hydroxyl radicals, with the formation of sev-eral intermediate products such as formaldehyde, formic acid, methanol and acetaldhehyde [2]. The TiO2 photodegradation of organic compounds has been proposed as an alternative Advanced Oxidation Processes (AOP) for the decontamination of air, since the photocatalytic oxidation of organic compounds in gas phase appears to be a promising process for the re-mediation of polluted air. In this paper the photocatalytic efficiency towards acetone degradation of four commercial samples, two micro-sized and two nano-sized TiO2 powders is com-pared. The purpose of this study is to evaluate the feasi-bility of using micro-sized TiO2 instead of nanometric particles, which results in a greater environmental im-pact and higher production costs if compared to the for-mer on

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

A 72-year-old man was admitted with one blade of a huge pair of shears in his left thorax. His hemodynamics deteriorated due to life-threatening vascular lesions. An urgent thoracotomy revealed several injuries to the intercostal vessels and left apical inferior lung lobe. The blade tip was stuck in the posterior chest wall, 2 cm adjacent to the descending aorta. The blade was removed, the lung was sutured, and the patient made a good recovery

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 “SHB”chiral Pc-L* Cu(I) complexes for continuous flow cyclopropanation reactions with carbon dioxide as a carrier

We have recently reported that copper(I) complexes of the new C1-symmetric pyridine-based 12-membered tetraaza macrocycles, Pyridine Containing Ligands (Pc-L*), are competent catalysts in the asymmetric cyclopropanation. In order to improve our catalytic system Cu(I) complexes based on Pc-L* ligands were heterogeneised on mesoporous ordered and non-ordered silicas (Davisil B, MCM-41, etc.) by the Supported by HydrogenBond (SHB) method. Supported catalysts C were tested in enantioselective cyclopropanation in batch conditions showing good catalytic activities employing ethyl diazoacetate (EDA) as carbene precursor in n-hexane. The silica support has a strong influence on the diastereoselective outcome of the reaction, favoring the formation of the more challenging cis-isomer. Then, C were tested as catalyst for the cyclopropanation reaction under flow conditions focusing our attention on the use of supercritical CO2. Under optimised conditions, the catalyst was stable over at least 10 h of continuous flow, without drop in activity or selectivity

The critical role of intragap states in the energy transfer from gold nanoparticles to TiO2

Cathodoluminescence spectroscopy is profitably exploited to study energy transfer mechanisms in Au and Pt/black TiO2 heterostructures. While Pt nanoparticles absorb light in the UV region, Au nanoparticles absorb light by surface plasmon resonance and interband transitions, both of them occurring in the visible region. The intra-bandgap states (oxygen vacancies) of black TiO2 play a key role in promoting both hot electron transfer and plasmonic resonant energy transfer from Au nanoparticles to the TiO2 semiconductor with a consequent photocatalytic H2 production increase. An innovative criterion is introduced for the design of plasmonic composites with increased efficiency under visible light