Influences of cation and anion substitutions on oxidative coupling of methane over hydroxyapatite catalysts

Abstract

Lead substituted hydroxyapatite (Pb-HAP) has been an active catalyst for oxidative coupling of methane (OCM) reactions. CO 3 2substituted HAP (HAP-CO 3) has showed enhanced oxide ion conductivity than bare HAP in high temperature solid oxide fuel cells. Substitutions for both cations and anions in HAP structure (Pb-HAP-CO 3) are promising to integrate the catalytic property of Pb-HAP and oxide ion conductive property of HAP-CO 3 into one apatite-based ceramic material that can be manufactured into membrane reactors for possessing CH 4 activation and O 2 permeation capabilities for efficient OCM reactions. In this work, the effects of substitutions for both cation (Pb 2+) and anion (CO 3 2-) in HAP structure on OCM reactions were studied. The composition and physicochemical properties of HAP catalysts were changed by the cation and anion substitutions, respectively, and as consequences, they influenced the catalytic performances of HAP structure in OCM reactions. The selectivity to C 2 (ethylene and ethane) products increased in the order of HAP-CO 3 < HAP < Pb-HAP-CO 3 < Pb-HAP, while Pb-HAP-CO 3 showed the best stability and comparable C 2 yield (under optimized reaction conditions) to Pb-HAP catalyst. Under different reaction temperature and/or CH 4 /O 2 ratio in the OCM reactions, the CH 4 conversion and C 2 or CO x (CO and CO 2) selectivity showed a strong dependence on the composition of HAP-based catalysts. The present study forms a basis for understanding of the correlations between the composition, structure, and catalytic performance of HAP and other apatite structured catalysts, which are potential membrane materials for OCM reactions in membrane reactors.

Glycerol valorization to lactic acid catalyzed by hydroxyapatite‐supported palladium particles

“…also were utilized to interpret the structural properties of the Pd/HAP catalysts. The detection of the vibration modes of the PO 4 3− groups in the HAP structure, namely the sharp and well‐defined peaks at ν1 (960–961 cm −1 ), ν2 (430–450 cm −1 ), ν3 (1035–1048 cm −1 and 1070–1075 cm −1 ) and ν4 (587–604 cm −1 ) confirms the apatite structure in all of the Pd/HAP catalysts …”

“…The detection of the vibration modes of the PO 4 3− groups in the HAP structure, namely the sharp and well-defined peaks at 1 (960-961 cm −1 ), 2 (430-450 cm −1 ), 3 (1035-1048 cm −1 and 1070-1075 cm −1 ) and 4 (587-604 cm −1 ) confirms the apatite structure in all of the Pd/HAP catalysts. 39,40 Fresh Pd 3 /HAP exhibits vibrational modes in the 645-651 cm −1 region, which is the main Raman mode of palladium oxide (PdO). However, this characteristic peak is absent in those catalysts with lower Pd loading.…”

Catalytic consequences of cation and anion substitutions on rate and mechanism of oxidative coupling of methane over hydroxyapatite catalysts

“…The synthesis of HAP-based catalysts was carried out by a co-precipitation method, as described in our previous work [36]. In the synthesis of bare mm radius hemispherical analyzer and eight channeltron detection system coupled with monochromatic Al radiation.…”

Preparation and characterization of Pt nanoparticles supported on a Fe‐doped hydroxyapatite‐activated Vulcan XC72 composite material

“…In the last few years, there has been a growing interest in hydroxyapatite (HAp), which is the major component in human hard tissue and has been applied to bones and synthesis of bioceramics . In addition, such as Ag, Ni, and Cu supported on HAp have been widely used as novel catalysts . Its structure is very good flexibility and high ion‐exchange capacity if the charge balance is maintained .…”