Gabriele Centi

Nanocarbons for the Development of Advanced Catalysts

Dang Sheng Su,*,†,‡ Siglinda Perathoner, and Gabriele Centi* †Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Science, 72 Wenhua Road, Shenyang 110006, China ‡Department of Inorganic Chemistry, Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany Dipartimento di Ingegneria Elettronica, Chimica ed Ingegneria Industriale, University of Messina and INSTM/CASPE (Laboratory of Catalysis for Sustainable Production and Energy), Viale Ferdinando Stagno, D’Alcontres 31, 98166 Messina, Italy

Catalysis for CO2 conversion: a key technology for rapid introduction of renewable energy in the value chain of chemical industries

Replacement of part of the fossil fuel consumption by renewable energy, in particular in the chemical industry, is a central strategy for resource and energy efficiency. This perspective will show that CO2 is the key molecule to proceed effectively in this direction. The routes, opportunities and barriers in increasing the share of renewable energy by using CO2 reaction and their impact on the chemical and energy value chains are discussed after introducing the general aspects of this topic evidencing the tight integration between the CO2 use and renewable energy insertion in the value chain of the process industry. The focus of this perspective article is on the catalytic aspects of the chemistries involved, with an analysis of the state-of-the-art, perspectives and targets to be developed. The reactions discussed are the production of short-chain olefins (ethylene, propylene) from CO2, and the conversion of carbon dioxide to syngas, formic acid, methanol and dimethyl ether, hydrocarbons via Fischer–Tropsch synthesis and methane. The relevance of availability, cost and environmental footprints of H2 production routes using renewable energies is addressed. The final part discusses the possible scenario for CO2 as an intermediary for the incorporation of renewable energy in the process industry, with a concise roadmap for catalysis needs and barriers to reach this goal.

Nature of active species in copper-based catalysts and their chemistry of transformation of nitrogen oxides

Abstract Copper-based catalysts are active in a wide range reactions of transformation of nitrogen oxides and represent an useful model system to better understand the fundamental aspects of the chemistry and mechanism of reaction of catalytic transformation of these pollutants. After an introduction on the reactivity of copper-based catalysts (supported and unsupported copper oxide, Cu-zeolites, cuprates and other copper compounds) in various reactions of conversion of nitrogen oxides, four main sub-topics are discussed in detail: (i) nature of copper species, (ii) chemisorption and surface transformations of NO, (iii) relationship between copper species and activity in the conversion of nitrogen oxides and (iv) mechanism of reduction of nitrogen oxides to N 2 . Five reactions of transformation of nitrogen oxides are discussed in detail: (i) decomposition of NO, (ii) reduction of NO with ammonia in the presence or not of oxygen, (iii) reduction of NO with hydrocarbons in the presence of oxygen, (iv) reduction of NO with CO and (v) decomposition of N 2 O. The mechanism of reduction of nitrite and N 2 O by copper enzymes is also discussed, with a view to provide some useful insights on the chemistry of transformation. In this review particular attention is directed towards controversial points in the literature, underestimated questions, and hypothesis and theories which do not allow interpretation of all sets of experimental data. Discussion is also focused on the presence of multiple and competitive pathways of transformation, the relative roles of which depend on reaction conditions.

Next-Generation Biofuels: Survey of Emerging Technologies and Sustainability Issues

Next-generation biofuels, such as cellulosic bioethanol, biomethane from waste, synthetic biofuels obtained via gasification of biomass, biohydrogen, and others, are currently at the center of the attention of technologists and policy makers in search of the more sustainable biofuel of tomorrow. To set realistic targets for future biofuel options, it is important to assess their sustainability according to technical, economical, and environmental measures. With this aim, the review presents a comprehensive overview of the chemistry basis and of the technology related aspects of next generation biofuel production, as well as it addresses related economic issues and environmental implications. Opportunities and limits are discussed in terms of technical applicability of existing and emerging technology options to bio-waste feedstock, and further development forecasts are made based on the existing social-economic and market situation, feedstock potentials, and other global aspects. As the latter ones are concerned, the emphasis is placed on the opportunities and challenges of developing countries in adoption of this new industry.

Towards Solar Fuels from Water and CO2

Solar fuels from water and CO2 are a topic of current large scientific and industrial interest. Research advances on bioroutes, concentrated solar thermal and low-temperature conversion using semiconductors and a photoelectrocatalytic (PEC) approach, are critically discussed and compared in an attempt to define challenges and current limits and to identify the priorities on which focus research and development (R&D). The need to produce fuels that are easy to transport and store, which can be integrated into the existing energy infrastructure, is emphasized. The role of solar fuels produced from CO2 in comparison with solar H2 is analyzed. Solar fuels are complementary to solar to electrical energy conversion, but they still need intensified R&D before possible commercialization.

Vanadyl Pyrophosphate - A Critical Overview

Abstract A critical overview of the recent literature data on the reaction mechanism and nature of the active sites, on the bulk vs. surface properties, on the kinetic aspects of butane oxidation and on the alternative uses of vanadyl pyrophosphate for other oxidation reactions is presented. Some important aspects that require further investigation in order to obtain a better understanding of the reaction mechanism and dynamics on a molecular scale, develop a general approach to catalysts for the selective alkane oxyfunctionalization and achieve further improvments in VPO catalyst performances in n-butane and n-pentane selective oxidation are discussed.

Nature and mechanism of formation of vanadyl pyrophosphate: Active phase in n-butane selective oxidation

The preparation of vanadium-phosphorus catalysts from V2O5/H3PO4/benzyl- and isobutyl alcohols leads to the formation of VOHPO4 · 12H2O with the organic alcohols trapped between the layers of the phosphate structure, which provoke disorder in the plane of layer stacking. During the successive calcination, a pseudomorphic (VO)2P2O7 forms with corresponding disorder in the plane of layer stacking. Disorder in this plane influences: (i) the catalytic activity in n-butane selective oxidation, and (ii) the redox properties of the catalyst, both modifying the rate of vanadium(IV) oxidation to V(V) and the reducibility of the catalyst in a flow of 1% n-butane/air. It is suggested that during calcination the alcohol induces the formation of local structural deformations which are responsible for the increase of activity in n-butane, but not in 1-butene, selective oxidation of the catalysts prepared in an organic solvent as compared with those prepared by precipitation in an aqueous solvent.

Nature of active layer in vanadium oxide supported on titanium oxide and control of its reactivity in the selective oxidation and ammoxidation of alkylaromatics

Abstract Vanadium oxide supported over titanium oxide is an important example of a transition-metal-oxide ‘monolayer’ catalyst with practical relevance for various industrial applications. After a brief introduction on the concept of monolayer oxide catalysts, this review examines three main topics: (i) the nature of vanadium oxide species over the titanium oxide surface, (ii) their reactivity and structure/activity-selectivity relationships and (iii) modification of the surface properties during the catalytic reactions of o -xylene oxidation and alkylaromatic ammoxidation. An analysis of selected literature data leads to the following main conclusions: (i) the support promotes the formation of an amorphous, hydrated active layer of titanium oxide which may extend up to 3–5 layers; (ii) the reactivity of titanium oxide in this form is enhanced with respect to crystalline vanadium oxide, but the selectivity properties which are a function of the oxidation state of vanadium ion and of the modifications occurring during the catalytic reaction are not significantly different; (iii) in the presence of ammonia, the characteristics of the catalyst surface must be tuned to limit the side reaction of NH 3 combustion. The optimal catalyst composition for ammoxidation reactions is thus different from that for oxidation catalysts. Simultaneous O and N insertion requires instead an intermediate catalyst composition between those optimal for oxidation and ammoxidation of alkylaromatics.

Environmental catalysis: trends and outlook

Abstract Environmental catalysis has continuously grown in importance over the last 2 decades not only in terms of the worldwide catalyst market, but also as a driver of advances in the whole area of catalysis. The development of innovative “environmental” catalysts is also the crucial factor towards the objective of developing a new sustainable industrial chemistry. In the last decade, considerable expansion of the traditional area of environmental catalysis (mainly NOx removal from stationary and mobile sources, and VOC conversion) has also occurred. New areas include: (i) catalytic technologies for liquid or solid waste reduction or purification; (ii) use of catalysts in energy-efficient catalytic technologies and processes; (iii) reduction of the environmental impact in the use or disposal of catalysts; (iv) new eco-compatible refinery, chemical or non-chemical catalytic processes; (v) catalysis for greenhouse gas control; (vi) use of catalysts for user-friendly technologies and reduction of indoor pollution; (vii) catalytic processes for sustainable chemistry; (viii) reduction of the environmental impact of transport. Therefore, a significant change has occurred in the last decade in the areas of interest regarding environmental catalysts and in the modality of approaching the research. This review, based on but not limited to the workshop “Environmental Catalysis: A Step Forward” (Maiori, Italy, May 2001), introduces the proceedings of this workshop reported in this issue of Catalysis Today and has the objective of providing an overview to the topic and setting the basis for a step forward in environmental catalysis research.

SUPPORTED PALLADIUM CATALYSTS IN ENVIRONMENTAL CATALYTIC TECHNOLOGIES FOR GASEOUS EMISSIONS

Palladium is the active component in several catalytic formulations for environmental technologies, due to its superior performances in the conversion of some hydrocarbons (for example, methane) and halocarbons, and the thermal stability and low volatility of Pd species. The properties and reactivity of Pd-based catalysts in the conversion of methane catalytic combustion for gas turbine applications, reduction of greenhouse gas (methane, N2O) emissions, hydrodehalogenation and oxidative destruction of halocarbons and their applications in the elimination of other pollutants from gaseous emissions are reviewed, with emphasis on the structure-activity relationships, reaction mechanism and sensitivity to poisoning.