There is increased recognition by the world’s scientific, industrial, and political communities that the concentrations of greenhouse gases in the earth’s
atmosphere, particularly CO_2, are increasing. For
example, recent studies of Antarctic ice cores to
depths of over 3600 m, spanning over 420 000 years,
indicate an 80 ppm increase in atmospheric CO_2 in
the past 200 years (with most of this increase
occurring in the past 50 years) compared to the
previous 80 ppm increase that required 10 000 years.2
The 160 nation Framework Convention for Climate
Change (FCCC) in Kyoto focused world attention on
possible links between CO2 and future climate change
and active discussion of these issues continues.3 In
the United States, the PCAST report4 “Federal
Energy Research and Development for the Challenges
of the Twenty First Century” focused attention
on the growing worldwide demand for energy and the
need to move away from current fossil fuel utilization.
According to the U.S. DOE Energy Information
Administration,5 carbon emission from the transportation
(air, ground, sea), industrial (heavy manufacturing,
agriculture, construction, mining, chemicals,
petroleum), buildings (internal heating, cooling, lighting),
and electrical (power generation) sectors of the
World economy amounted to ca. 1823 million metric
tons (MMT) in 1990, with an estimated increase to
2466 MMT in 2008-2012 (Table 1).

Catalysis Research of Relevance to Carbon Management: Progress, Challenges, and Opportunities

https://dspace.library.uu.nl/bitstream/handle/1874/26040/Catal.Today-Weckhuysen-2003.pdf?sequence=1

Chemistry, spectroscopy and the role of supported vanadium oxides in heterogeneous catalysis

Supported vanadium oxide catalysts, containing surface vanadia species on oxide supports, are extensively employed as catalysts for many hydrocarbon oxidation reactions. This paper discusses the current fundamental information available about the structure and reactivity of surface vanadia species on oxide supports: monolayer surface coverage, stability of the surface vanadia monolayer, oxidation state of the surface vanadia species, molecular structures of the surface vanadia species (as a function of environment and catalyst composition), acidity of the surface vanadia species and reactivity of the surface vanadia species. Comparison of the molecular structure and reactivity information provides new fundamental insights into the catalytic properties of surface vanadia species during hydrocarbon oxidation reactions: (1) the role of terminal VO, bridging VOV and bridging VO-support bonds, (2) the number of surface vanadia sites required, (3) the influence of metal oxide additives, (4) the influence of surface acidic and basic sites, (5) the influence of preparation methods and (6) the influence of the specific oxide support phase. The unique physical and chemical characteristics of supported vanadia catalysts, compared to other supported metal oxide catalysts, for hydrocarbon oxidation reactions are also discussed.

/pdf/structure-and-reactivity-of-surface-vanadium-oxide-species-2t480mfj4r.pdf

Structure and reactivity of surface vanadium oxide species on oxide supports

This paper summarizes the main data appeared in the last years on the oxidative dehydrogenation (ODH) of short chain alkanes on supported vanadium oxide catalysts. The acid-base character of metal oxide support influences the dispersion of vanadium on the surface of the support, as well as the nature of the vanadium species. The reducibility and structure of surface vanadium oxide species and the acid-base character of catalysts, in addition to their catalytic properties in the ODH of C2–C4 alkanes, strongly depend on the metal oxide used as support and the vanadium loading. In this way, it appears that tetrahedral V5+-species are active and selective sites in the ODH of C2–C4 alkanes. The effect of the coordination number and aggregation state of surface vanadium oxide species, and the presence of acid/base sites on the catalytic behavior of supported vanadium oxide catalysts are discussed. It is concluded that these are important factors that must be considered to develop selective catalysts in ODH reactions.

Oxidative dyhydrogenation of short chain alkanes on supported vanadium oxide catalysts

This review summarizes published data on catalytic performances of different vanadium-containing oxides, including unsupported and supported V2O5, vanadates, solid solutions and mixed phases, in the oxidative dehydrogenation of C2–C5 alkanes. The analysis of the structure-activity relationships shows that various species characterized by a different reactivity exist on the surface of these catalysts. There are some indications that tetrahedral vanadium species are the most favourable for alkane oxidehydrogenation. Its intrinsic activity seems to be largely dependent on the structure of the nearest surrounding and, therefore, can be modified by changing the nature and number of the neighbouring ions. Although the reaction mechanism is generally accepted to be through the redox cycle between V5+ and V4+, opposite relationships between catalyst activity/selectivity and reducibility have been established, even for the same catalytic systems. No clear interpretation regarding the mode of alkane activation can be derived from a survey of the literature. This and some other aspects of the reaction mechanism need further studies at a molecular level.

Oxidative dehydrogenation of lower alkanes on vanadium oxide-based catalysts. The present state of the art and outlooks

Selectivity Patterns in Alkane Oxidation over Mg3(VO4)2-MgO, Mg2V2O7, and (VO)2P2O7

Selective Oxidation of Pentane over Al2O3- and SiO2-Supported Vanadia Catalysts

The catalytic oxidation of ethane, propane, 2-methylpropane, butane, pentane, and cyclohexane has been studied over Mg3(VO4)2-MgO, Mg2V2O7, and (VO)2P2O7. These reactions produced a wide range of products ranging from alkenes, dienes, anhydrides, acids, and carbon oxides. Broadly speaking, the major products were dehydrogenation products over Mg3(VO4)2, combustion products over Mg2V2O7, and oxygen-containing organic products over (VO)2P2O7, although there are exceptions to this broad generalization. From the product selectivities, the moles of oxygen consumed per mole of alkane reacted could be calculated. These were the average oxygen stoichiometries for the reactions. They had values of about unity for ethane oxidation over VPO, about two when oxidative dehydrogenation was the predominant reaction, and about four for the other reactions studied. The selectivity patterns in terms of the formation of dehydrogenation products versus oxygen-containing products including carbon oxides were explained by assuming that there existed a selectivity-determining step, which could be the reaction of the surface alkyl species or the adsorbed alkene before its desorption. The formation of oxygen-containing products would be facilitated if the surface alkyl or adsorbed alkene could interact with the vanadium ions in two adjacent VOx units such that it could easily react with the reactive oxygen in the V-O-V bridge. The results of ethane oxidation, however, could not be explained simply by this model, and other factors needed to be considered.

P.M. Michalakos

Papers

Selectivity Patterns in Alkane Oxidation over Mg3(VO4)2-MgO, Mg2V2O7, and (VO)2P2O7

Selective Oxidation of Pentane over Al2O3- and SiO2-Supported Vanadia Catalysts

Selectivity Patterns in Alkane Oxidation Over Mg3(VO4)2-MgO, Mg2V2O7, and (VO)2P2O7.