Reduction of NO by CO on Cu/ZrO(2)/Al(2)O(3) catalysts: Characterization and catalytic activities

ZrO(2), gamma-Al(2)O(3) and ZrO(2)/gamma-Al(2)O(3)-supported copper catalysts have been prepared, each with three different copper loads (1, 2 and 5 wt%), by the impregnation method. The catalysts were characterized by nitrogen adsorption (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR) with H(2), Raman spectroscopy and electronic paramagnetic resonance (EPR). The reduction of NO by CO was studied in a fixed-bed reactor packed with these catalysts and fed with a mixture of 1% CO and 1% NO in helium. The catalyst with 5 wt% copper supported on the ZrO(2)/gamma-Al(2)O(3) matrix achieved 80% reduction of NO. Approximately the same rate of conversion was obtained on the catalyst with 2 wt% copper on ZrO(2). Characterization of these catalysts indicated that the active copper species for the reduction of NO are those in direct contact with the oxygen vacancies found in ZrO(2). (C) 2009 Published by Elsevier Ltd.

Influence of support on catalytic behavior of nickel catalysts in the steam reforming of ethanol for hydrogen production

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

EFFECTS OF ADDING LANTHANUM TO Ni/ZrO2 CATALYSTS ON ETHANOL STEAM REFORMING

EFFECTS OF ADDING LANTHANUM TO Ni/ZrO2 CATALYSTS ON ETHANOL STEAM REFORMING. The catalytic performance of Ni/ZrO2 catalysts loaded with different lanthanum content for steam reforming of ethanol was investigated. Catalysts were characterized by BET surface area, X-ray diffraction, UV-vis spectroscopy, temperature programmed reduction, and X-ray absorption fine structure techniques. Results showed that lanthanum addition led to an increase in the degree of reduction of both NiO and nickel surface species interacting; with the support, due to the higher dispersion effect. The best catalytic performance at 450 degrees C was found for the Ni/2LZ catalyst, which exhibited an effluent gaseous mixture with the highest H-2 yield.

Structural changes and dynamic behaviour of vanadium oxide-based catalysts for gas-phase selective oxidations

Selective oxidation is one of the simplest functionalization methods and essentially all monomers used in manufacturing artificial fibers and plastics are obtained by catalytic oxidation processes. Formally, oxidation is considered as an increase in the oxidation number of the carbon atoms, then reactions such as dehydrogenation, ammoxidation, cyclization or chlorination are all oxidation reactions. In this field, most of processes for the synthesis of important chemicals used vanadium oxide-based catalysts. These catalytic systems are used either in the form of multicomponent mixed oxides and oxysalts, e.g., in the oxidation of n-butane (V/P/O) and of benzene (supported V/Mo/O) to maleic anhydride, or in the form of supported metal oxide, e.g., in the manufacture of phthalic anhydride by o-xylene oxidation, of sulphuric acid by oxidation of SO2, in the reduction of NOx with ammonia and in the ammoxidation of alkyl aromatics. In addition, supported vanadia catalysts have also been investigated for the oxidative dehydrogenation of alkanes to olefins , oxidation of pentane to maleic anhydride and the selective oxidation of methanol to formaldehyde or methyl formate [1]. During my PhD I focused my work on two gas phase selective oxidation reactions. The work was done at the Department of Industrial Chemistry and Materials (University of Bologna) in collaboration with Polynt SpA. Polynt is a leader company in the development, production and marketing of catalysts for gas-phase oxidation. In particular, I studied the catalytic system for n-butane oxidation to maleic anhydride (fluid bed technology) and for o-xylene oxidation to phthalic anhydride. Both reactions are catalyzed by systems based on vanadium, but catalysts are completely different. Part A is dedicated to the study of V/P/O catalyst for n-butane selective oxidation, while in the Part B the results of an investigation on TiO2-supported V2O5, catalyst for o-xylene oxidation are showed. In Part A, a general introduction about the importance of maleic anhydride, its uses, the industrial processes and the catalytic system are reported. The reaction is the only industrial direct oxidation of paraffins to a chemical intermediate. It is produced by n-butane oxidation either using fixed bed and fluid bed technology; in both cases the catalyst is the vanadyl pyrophosphate (VPP). Notwithstanding the good performances, the yield value didn’t exceed 60% and the system is continuously studied to improve activity and selectivity. The main open problem is the understanding of the real active phase working under reaction conditions. Several articles deal with the role of different crystalline and/or amorphous vanadium/phosphorous (VPO) compounds. In all cases, bulk VPP is assumed to constitute the core of the active phase, while two different hypotheses have been formulated concerning the catalytic surface. In one case the development of surface amorphous layers that play a direct role in the reaction is described, in the second case specific planes of crystalline VPP are assumed to contribute to the reaction pattern, and the redox process occurs reversibly between VPP and VOPO4. Both hypotheses are supported also by in-situ characterization techniques, but the experiments were performed with different catalysts and probably under slightly different working conditions. Due to complexity of the system, these differences could be the cause of the contradictions present in literature. Supposing that a key role could be played by P/V ratio, I prepared, characterized and tested two samples with different P/V ratio. Transformation occurring on catalytic surfaces under different conditions of temperature and gas-phase composition were studied by means of in-situ Raman spectroscopy, trying to investigate the changes that VPP undergoes during reaction. The goal is to understand which kind of compound constituting the catalyst surface is the most active and selective for butane oxidation reaction, and also which features the catalyst should possess to ensure the development of this surface (e.g. catalyst composition). On the basis of results from this study, it could be possible to project a new catalyst more active and selective with respect to the present ones. In fact, the second topic investigated is the possibility to reproduce the surface active layer of VPP onto a support. In general, supportation is a way to improve mechanical features of the catalysts and to overcome problems such as possible development of local hot spot temperatures, which could cause a decrease of selectivity at high conversion, and high costs of catalyst. In literature it is possible to find different works dealing with the development of supported catalysts, but in general intrinsic characteristics of VPP are worsened due to the chemical interaction between active phase and support. Moreover all these works deal with the supportation of VPP; on the contrary, my work is an attempt to build-up a V/P/O active layer on the surface of a zirconia support by thermal treatment of a precursor obtained by impregnation of a V5+ salt and of H3PO4. In-situ Raman analysis during the thermal treatment, as well as reactivity tests are used to investigate the parameters that may influence the generation of the active phase. Part B is devoted to the study of o-xylene oxidation of phthalic anhydride; industrially, the reaction is carried out in gas-phase using as catalysts a supported system formed by V2O5 on TiO2. The V/Ti/O system is quite complex; different vanadium species could be present on the titania surface, as a function of the vanadium content and of the titania surface area: (i) V species which is chemically bound to the support via oxo bridges (isolated V in octahedral or tetrahedral coordination, depending on the hydration degree), (ii) a polymeric species spread over titania, and (iii) bulk vanadium oxide, either amorphous or crystalline. The different species could have different catalytic properties therefore changing the relative amount of V species can be a way to optimize the catalytic performances of the system. For this reason, samples containing increasing amount of vanadium were prepared and tested in the oxidation of o-xylene, with the aim of find a correlations between V/Ti/O catalytic activity and the amount of the different vanadium species. The second part deals with the role of a gas-phase promoter. Catalytic surface can change under working conditions; the high temperatures and a different gas-phase composition could have an effect also on the formation of different V species. Furthermore, in the industrial practice, the vanadium oxide-based catalysts need the addition of gas-phase promoters in the feed stream, that although do not have a direct role in the reaction stoichiometry, when present leads to considerable improvement of catalytic performance. Starting point of my investigation is the possibility that steam, a component always present in oxidation reactions environment, could cause changes in the nature of catalytic surface under reaction conditions. For this reason, the dynamic phenomena occurring at the surface of a 7wt% V2O5 on TiO2 catalyst in the presence of steam is investigated by means of Raman spectroscopy. Moreover a correlation between the amount of the different vanadium species and catalytic performances have been searched. Finally, the role of dopants has been studied. The industrial V/Ti/O system contains several dopants; the nature and the relative amount of promoters may vary depending on catalyst supplier and on the technology employed for the process, either a single-bed or a multi-layer catalytic fixed-bed. Promoters have a quite remarkable effect on both activity and selectivity to phthalic anhydride. Their role is crucial, and the proper control of the relative amount of each component is fundamental for the process performance. Furthermore, it can not be excluded that the same promoter may play different role depending on reaction conditions (T, composition of gas phase..). The reaction network of phthalic anhydride formation is very complex and includes several parallel and consecutive reactions; for this reason a proper understanding of the role of each dopant cannot be separated from the analysis of the reaction scheme. One of the most important promoters at industrial level, which is always present in the catalytic formulations is Cs. It is known that Cs plays an important role on selectivity to phthalic anhydride, but the reasons of this phenomenon are not really clear. Therefore the effect of Cs on the reaction scheme has been investigated at two different temperature with the aim of evidencing in which step of the reaction network this promoter plays its role.

Development of innovative catalysts for the hydrodechlorination to fluoroethers

In this work the hydrodechlorination of CF3OCFClCF2Cl to produce unsaturated CF3OCF=CF2 was studied over a series of supported metal catalysts. Currently this molecule is produced from the precursor CF3OCFClCF2Cl by dechlorination with zinc powder. An important cost on the economic and environmental balance is represents by the large amount of ZnCl2 produced and to be disposed of. A new approach, based on gas-phase hydrodechlorination over supported catalysts can lead to a new sustainable process. During the feasibility step of this project, substantially two kind of materials were studied: metals supported over activated carbon and Pd/Cu species supported over MCM-41 mesoporous silica. Observed catalytic performances were strongly dependent on the metal and support used. All carbon-supported Ru, Pd, and bimetallic catalysts are fairly active and yielded the target product CF3OCF=CF2, the higher selectivity being obtained with ruthenium- and palladium-based materials. Nevertheless, Ru-based catalysts showed poor stability and this deactivation may be attributed to the deposition of chlorinated organic species blocking the active sites. On the other hand, palladium-containing catalysts showed high stability. Ru/Pd and Pd/Cu bimetallic catalysts exhibited long-term selectivity and stability, highlighting the possibility for these materials to be employed in the CF3OCF=CF2 production process. During the second part of this thesis, a series of bimetallic meso-structured Pd/Cu MCM-41 catalysts were studies to overcome possible mass transfer limitations. The materials were obtained by different synthesis methods. The incorporation of Pd and Cu during MCM-41 synthesis, did not destroy the typical hexagonal array and ordered pore system of MCM-41. However, the calcination for the removal of the template provoked significant segregation of oxides. The impregnation leads to pore-occlusion and formation of Cu particles and large bimetallic PdCu species. Larger metal particles leads to lower CF3OCFClCF2Cl conversion, while the monometallic particles can decrease the selectivity to CF3OCF=CF2, fostering the dehalogenation to CF3OCH=CF2.

Sonochemical synthesis of graphene oxide supported Pt–Pd alloy nanocrystals as efficient electrocatalysts for methanol oxidation

Pt–Pd bimetallic nanoparticles supported on graphene oxide (GO) nanosheets were prepared by a sonochemical reduction method in the presence of polyethylene glycol as a stabilizing agent. The synthetic method allowed for a fine tuning of the particle composition without significant changes in their size and degree of aggregation. Detailed characterization of GO-supported Pt–Pd catalysts was carried out by transmission electron microscopy (TEM), AFM, XPS, and electrochemical techniques. Uniform deposition of Pt–Pd nanoparticles with an average diameter of 3 nm was achieved on graphene nanosheets using a novel dual-frequency sonication approach. GO-supported bimetallic catalyst showed significant electrocatalytic activity for methanol oxidation. The influence of different molar compositions of Pt and Pd (1:1, 2:1, and 3:1) on the methanol oxidation efficiency was also evaluated. Among the different Pt/Pd ratios, the 1:1 ratio material showed the lowest onset potential and generated the highest peak current density. The effect of catalyst loading on carbon paper (working electrode) was also studied. Increasing the catalyst loading beyond a certain amount lowered the catalytic activity due to the aggregation of metal particle-loaded GO nanosheets.

CeO2-promoted Ni/activated carbon catalysts for the water–gas shift (WGS) reaction

The low temperature water–gas shift (WGS) reaction has been studied over carbon-supported nickel catalysts promoted by ceria. To this end, cerium oxide has been dispersed (at different loadings: 10, 20, 30 and 40 wt.%) on the activated carbon surface with the aim of obtaining small ceria particles and a highly available surface area. Furthermore, carbon- and ceria-supported nickel catalysts have also been studied as references. A combination of N2 adsorption analysis, powder X-ray diffraction, temperature-programmed reduction with H2, X-ray photoelectron spectroscopy and TEM analysis were used to characterize the Ni–CeO2 interactions and the CeO2 dispersion over the activated carbon support. Catalysts were tested in the low temperature WGS reaction with two different feed gas mixtures: the idealized one (with only CO and H2O) and a slightly harder one (with CO, CO2, H2, and H2O). The obtained results show that there is a clear effect of the ceria loading on the catalytic activity. In both cases, catalysts with 20 and 10 wt.% CeO2 were the most active materials at low temperature. On the other hand, Ni/C shows a lower activity, this assessing the determinant role of ceria in this reaction. Methane, a product of side reactions, was observed in very low amounts, when CO2 and H2 were included in the WGS feed. Nevertheless, our data indicate that the methanation process is mainly due to CO2, and no CO consumption via methanation takes place at the relevant WGS temperatures. Finally, a stability test was carried out, obtaining CO conversions greater than 40% after 150 h of reaction.

Recent advances in catalysts for methanol synthesis via hydrogenation of CO and CO2

Since the start of last century, methanol synthesis has attracted great interests because of its importance in chemical industries and its potential as an environmentally friendly energy carrier. The catalyst for the methanol synthesis has been a key area of research in order to optimize the reaction process. In the literature, the nature of the active site and the effects of the promoter and support have been extensively investigated. In this updated review, the recent progresses in the catalyst innovation, optimization of the reaction conditions, reaction mechanism, and catalyst performance in methanol synthesis are comprehensively discussed. Key issues of catalyst improvement are highlighted, and areas of priority in R&D are identified in the conclusions.

Role of nanosized zirconia on the properties of Cu/Ga2O3/ZrO2 catalysts for methanol synthesis

The introduction of mesoporous nanosize zirconia to the catalyst for methanol synthesis dedicates the nanosized catalyst and mesoporous duplicated properties. The catalyst bears the larger surface area, larger mesoporous volume and more uniform diameter, more surface metal atoms and oxygen vacancies than the catalyst prepared with the conventional coprecipitation method. The modification of microstructure and electronic effect could result in the change of the reduced chemical state and decrease of reducuction temperature of copper, donating the higher activity and methanol selectivity to the catalyst. The results of methanol synthesis demonstrate that the Cu+ is the optimum active site. Also, the interaction between the copper and zirconia shows the synergistic effect to fulfil the methanol synthesis.

Platinum–tin/carbon catalysts for ethanol oxidation: Influence of Sn content on the electroactivity and structural characteristics

Carbon-supported Pt–Sn catalysts commonly contain Pt–Sn alloy and/or Pt–Sn bimetallic systems (Sn oxides). Nevertheless, the origin of the promotion effect due to the presence of Sn in the Pt–Sn/C catalyst towards ethanol oxidation in acid media is still under debate and some contradictions. Herein, a series of Ptx–Sny/C catalysts with different atomic ratios are synthesized by a deposition process using formic acid as the reducing agent. Catalysts structure and chemical compositions are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) and their relationship with catalytic behavior towards ethanol electro-oxidation was established. Geometric structural changes are producing by highest Sn content (Pt1–Sn1/C) promoted the interaction of Pt and Sn forming a solid solution of Pt–Sn alloy phase, whereas, the intermediate and lowest Sn content (Pt2–Sn1/C and Pt3–Sn1/C, respectively) promoted the electronic structure modifications of Pt by Sn addition without the formation of a solid solution. The amount of Sn added affects the physical and chemical characteristics of the bimetallic catalysts as well as reducing the amount of Pt in the catalyst composition and maintaining the electrocatalytic activities at the anode. However, the influence of the Sn oxidation state in Pt–Sn/C catalysts surfaces and the alloy formation between Pt and Sn as well as with the atomic ratio on their catalytic activity towards ethanol oxidation appears minimal. Similar methodologies applied for synthesis of Ptx–Sny/C catalysts with a small change show differences with the results obtained, thus highlighting the importance of the conditions of the preparation method.

Cobalt carbonate hydroxide nanowire array on ti mesh: an efficient and robust 3D catalyst for on-demand hydrogen generation from alkaline naBH4 solution.

In this work, for the first time, a cobalt carbonate hydroxide (Co(CO3 )0.5 (OH)⋅0.11 H2 O) nanowire array on Ti mesh (CHNA/Ti) was applied to drive the dehydrogenation of alkaline NaBH4 solution for on-demand hydrogen production. Compared with other nanostructured Co-based catalyst systems, CHNA/Ti can be activated more quickly and separated easily from fuel solutions. This self-supported cobalt salt nanowire array catalyst works as an efficient and robust 3D catalyst for the hydrolysis reaction of NaBH4 with a hydrogen generation rate of 4000 mL min(-1)  gCo (-1) and a low apparent activation energy of 39.78 kJ mol(-1) and offers an attractive system for on-demand hydrogen generation.

CO2 reforming of toluene as model compound of biomass tar on Ni/Palygorskite

Catalytic CO2 reforming of biomass tar on palygorskite-supported nickel catalysts using toluene as a model compound of biomass tar was investigated. The experiments were performed in a bench scale installation a fixed bed reactor. All experiments were carried out at 650, 750, 800 °C and atmospheric pressure. The effect of Ni loading, reaction temperature and concentration of CO2 on H2 yield and carbon deposit was investigated. Ni/Palygorskite (Ni/PG) catalysts with Ni/PG ratios of 0%, 2%, 5% and 8% were tested, the last two show the best performance. H2 yield and carbon deposit diminished with the increase of reaction temperature, Ni loading, and CO2 concentration.

Ultrafast Microwave-Assisted Route to Surfactant-Free Ultrafine Pt Nanoparticles on Graphene: Synergistic Co-reduction Mechanism and High Catalytic Activity

We demonstrate an ultrafast method for the formation of, graphene supported Pt catalysts by the co-reduction of graphene oxide and Pt salt using ethylene glycol under microwave irradiation conditions. Detailed analysis of the mechanism of formation of the hybrids indicates a synergistic co-reduction mechanism whereby the presence of the Pt ions leads to a faster reduction of GO and the presence of the defect sites on the reduced GO serves as anchor points for the heterogeneous nucleation of Pt. The resulting hybrid consists of ultrafine nanoparticles of Pt uniformly distributed on the reduced GO susbtrate. We have shown that the hybrid exhibits good catalytic activity for methanol oxidation and hydrogen conversion reactions. The mechanism is general and applicable for the synthesis of other multifunctional hybrids based on graphene.

Nanoflowers of PdRu on PEDOT for Electrooxidation of Glycerol and Its Analysis

Poly(3,4-ethylenedioxythiophene) (PEDOT) supported PdRu catalysts with various Pd:Ru atomic ratios are prepared by one step electrodeposition method. The catalysts are characterised by several physico-chemical techniques. The morphology depends on Pd:Ru ratio. The nanoflowers of Pd5Ru catalyst are deposited on PEDOT surface in an alloy form. Cyclic voltammetry experiments indicate that Ru improves the catalytic activity of Pd for glycerol oxidation significantly. However, the oxidation of glycerol is not observed on Ru-PEDOT/C electrode. Amongst all compositions, Pd5Ru nanoflowers on PEDOT exhibit the highest electrocatalytic activity and stability. Cyclic voltammetry and differential pulse voltammetry experiments are performed for the analysis of glycerol. Pd5Ru-PEDOT/C electrode is highly sensitive towards glycerol detection with sensitivity of 99.8 mu A cm(-2) mu M-1 and low detection limit of 0.1 mu M. Thus, electrochemically deposited nanoflowers Pd5Ru on PEDOT are efficient catalysts for direct glycerol oxidation as well as for analysis in alkaline media. (C) 2015 Elsevier Ltd. All rights reserved.

Investigations of group IVA transition metal mediated carbon-carbon bond forming reactions

Zirconocene aldehyde and ketone complexes were synthesized in high yield by treatment of zirconocene acyl complexes with trimethylaluminum or diisobutylaluminum hydride. These complexes, which are activated by dialkylaluminum chloride ligands, inserted unsaturated substrates such as alkynes, allenes, ethylene, nitriles, ketenes, aldehydes, ketones, lactones, and acid chlorides with moderate to high conversion. Insertion of aldehyde substrates yielded zirconocene diolate complexes with up to 20:1 (anti:syn) diastereoselectivity. The zirconocene diolates were hydrolyzed to afford unsymmetrical 1,2-diols in 40-80% isolated yield. Unsymmetrical ketones gave similar insertion yields with little or no diastereoselectivity. A high yielding one-pot method was developed that coupled carbonyl substrates with zirconocene aldehyde complexes that were derived from olefins by hydrozirconation and carbonylation. The zirconocene aldehyde complexes also inserted carbon monoxide and gave acyloins in 50% yield after hydrolysis.

The insertion reaction of aryl epoxides with the trimethylphoshine adduct of titanocene methylidene was examined. The resulting oxytitanacyclopentanes were carbonylated and oxidatively cleaved with dioxygen to afford y-lactones in moderate yields. Due to the instability and difficult isolation of titanocene methylidene trimethylphoshine adducts, a one-pot method involving the addition of catalytic amounts of trimethylphosphine to β,β-dimethyltitanacyclobutane was developed. A series of disubstituted aryl epoxides were examined which gave mixtures of diastereomeric insertion products. Based on these results, as well as earlier Hammett studies and labeling experiments, a biradical transition state intermediate is proposed. The method is limited to aryl substituted epoxide substrates with aliphatic examples showing no insertion reactivity.

The third study involved the use of magnesium chloride supported titanium catalysts for the Lewis acid catalyzed silyl group transfer condensation of enol silanes with aldehydes. The reaction resulted in silylated aldol products with as many as 140 catalytic turnovers before catalyst inactivation. Low diastereoselectivities favoring the anti-isomer were consistent with an open transition state involving a titanium atom bound to the catalyst surface. The catalysts were also used for the aldol group transfer polymerization of t-butyldimethylsilyloxy-1-ethene resulting in polymers with molecular weights of 5000-31,000 and molar mass dispersities of 1.5-2.8. Attempts to polymerize methylmethacrylate using GTP proved unsuccessful with these catalysts.