Catalytic consequences of cation and anion substitutions on rate and mechanism of oxidative coupling of methane over hydroxyapatite catalysts. (1st March 2017)

• Record Type: Journal Article
• Authors: Oh, Su Cheun; Lei, Yu; Chen, Huiyong; Liu, Dongxia
• Is Part Of: Fuel. Volume 191(2017)
• Page Start: 472
• Page End: 485
• Publication Date: 2017-03-01
• Subjects: Hydroxyapatite -- Anion and cation substitution -- Oxidative coupling of methane -- Pb-hydroxyapatite -- Kinetics; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2016.11.106
• Languages: English
• ISSNs: 0016-2361

Abstract

Graphical abstract: Highlights: Pb 2+, F − and both substitutions in hydroxyapatite (HAP) were studied. Both Pb 2+ and F − substitutions in HAP favored C2 H6 formation. Kinetics of primary reactions on Pb-HAP and Pb-HAP-F was analyzed by Eley-Rideal mechanism. Kinetics of primary reactions on HAP and HAP-F was analyzed by Langmuir-Hinshelwood mechanism. Composition-catalytic performance correlations for HAP-based catalysts were established. Abstract: The identity and rate constants of elementary steps in primary reactions of oxidative coupling of methane (OCM) over Pb 2+ and/or F − substituted hydroxyapatite (HAP, Pb-HAP, HAP-F, and Pb-HAP-F) catalysts have been studied. The rigorous kinetics analysis suggests that HAP and HAP-F initiated the reaction between adsorbed methane and O2 following Langmuir-Hinshelwood behavior. The Pb-HAP and Pb-HAP-F, however, enabled the reaction between gaseous methane and adsorbed O2 in the Eley-Rideal mechanism. The F − substitution of OH − weakened both O2 adsorption and CH bond activation, leading to low methane conversion and slightly higher C2 H6 selectivity. The substitution of Ca 2+ by Pb 2+ weakened both methane and oxygen adsorptions, but maintained CH bond activation and raised C2 H6 selectivity. The present analysis explored for the first time the effects of cation and/or anion in HAP on OCM reactions in which the analysis has been detailed and quantified in the nature of the mechanism-based kinetic models.