Oxygen Sites at Molybdena and Vanadia Surfaces: Energetics of the Re-Oxidation Process

[img]PDF - Authorized users only
Language: English
2027Kb
Title:Oxygen Sites at Molybdena and Vanadia Surfaces: Energetics of the Re-Oxidation Process
Creators:
Tokarz-Sobieraj, Renata
Grybos, Robert
Witko, Małgorzata
Hermann, Klaus
Journal or Publication Title:
Collection of Czechoslovak Chemical Communications, 69, 1, pp. 121-140
Uncontrolled Keywords:Oxidations, Active sites, Heterogeneous catalysis, Molybdenum and vanadium oxides, Reaction mechanism, Surface re-oxidation, DFT calculations

Abstract

In oxidation reactions proceeding in accordance with the Mars-van Krevelen mechanism lattice oxygen plays the role of an oxidizing agent. Surface vacancies created by incorporation of lattice oxygen into reacting molecules are filled in a subsequent step by gaseous oxygen or, if not enough oxygen is present in the reaction environment, by oxygen diffusion from the bulk. During this process, a very active, electrophilic surface oxygen species may be formed. In effect, total combustion takes place decreasing the selectivity for partial oxidation products. The thermodynamic aspect of this effect (neglecting reaction barriers) is demonstrated for molybdenum trioxide and vanadium pentoxide. On the catalytically most interesting surfaces, MoO<sub>3</sub>(010) and V<sub>2</sub>O<sub>5</sub>(010), three structurally different types of oxygen sites are present which exhibit different properties with respect to vacancy creation and annihilation. Re-oxidation of the catalyst by gaseous oxygen leads to oxygen molecules adsorbed in vacancies, preferably in an orientation parallel to the surface. Adsorption of the oxygen molecule in the vacancy leads to its activation followed by easy release of a neutral oxygen atom, which can be identified as the electrophilic species responsible for total combustion. <p>

Title:Oxygen Sites at Molybdena and Vanadia Surfaces: Energetics of the Re-Oxidation Process
Creators:
Tokarz-Sobieraj, Renata
Grybos, Robert
Witko, Małgorzata
Hermann, Klaus
Uncontrolled Keywords:Oxidations, Active sites, Heterogeneous catalysis, Molybdenum and vanadium oxides, Reaction mechanism, Surface re-oxidation, DFT calculations
Divisions:Life and Chemical Sciences > Institute of Organic Chemistry and Biochemistry > Collection of Czechoslovak Chemical Communications
Journal or Publication Title:Collection of Czechoslovak Chemical Communications
Volume:69
Number:1
Page Range:pp. 121-140
ISSN:0010-0765
E-ISSN:1212-6950
Publisher:Institute of Organic Chemistry and Biochemistry
Related URLs:
URLURL Type
http://dx.doi.org/10.1135/cccc20040121UNSPECIFIED
ID Code:2200
Item Type:Article
Deposited On:06 Feb 2009 17:16
Last Modified:06 Feb 2009 16:16

Citation

Tokarz-Sobieraj, Renata; Grybos, Robert; Witko, Małgorzata; Hermann, Klaus (2004) Oxygen Sites at Molybdena and Vanadia Surfaces: Energetics of the Re-Oxidation Process. Collection of Czechoslovak Chemical Communications, 69 (1). pp. 121-140. ISSN 0010-0765

Repository Staff Only: item control page