Selective Oxidation of Ethane Over Mo–V–Al–O Oxide Catalysts: Insight to the Factors Affecting the Selectivity of Ethylene and Acetic Acid and Structure-activity Correlation Studies

Abstract

Catalysts of general formula, MoVAlO x were prepared with the initial elemental composition of 1:0.34:0.167 (Mo:V:Al) at a pH value in the range of 1-4. The elemental analysis showed that the final composition of the catalysts is pH dependant. The performance of the catalysts was tested for selective oxidation of ethane to give ethylene and acetic acid. While all of them were active for ethane oxidation with a moderate conversion, the catalyst prepared at pH 2 showed a highest activity with 23% ethane conversion and a combined selectivity of 80.6% to ethylene and acetic acid. The catalyst prepared at pH 4 was least selective to ethylene and acetic acid. Various techniques like powder XRD, SEM, Raman, UV-Vis and EPR were used to characterize the catalysts and to identify the active phases responsible for the selective oxidation of ethane. The powder XRD data showed that the catalysts prepared at pH 1 and 2 contain mainly of MoO 3 and MoV 2 O 8 along with traces of Mo 4 O 11 . The amount of MoO 3 was slightly higher in the catalyst prepared at pH 1. However, the catalyst prepared at pH 3 contains mainly of MoV 2 O 8 with no trace of MoO 3 . The catalyst prepared at pH 4 showed V 2 O 5 as the major phase along with MoVAlO 4 phase. The Raman data corroborated the XRD results. EPR and UV-Vis studies indicated the presence of traces of V 4+ in pH 1 and 2 catalysts and significant amount of Mo 5+ in all the catalysts. Thus, the high activity and selectivity to ethylene and acetic acid are attributed to the presence of MoV 2 O 8 phase and other reduced species like Mo 4 O 11 phase supported on MoO 3 . The presence of V and Mo ions in a partially reduced form seems to play a crucial role in the selective oxidation of ethane.

Thermal treatments of precursors of molybdenum and vanadium oxides and the formed Mo x V y O z phases active in the oxydehydration of glycerol

“…It could be concluded from the combined results of the characterization techniques that the partial removal of oxygen anions from MoV 2 O 8 did not change the crystallographic pattern. Consequently, the MoV 2 O 8 structure seems to be sufficiently flexible to accommodate the anionic vacancies without structural collapse, with fast oxygen transfer and oxygen/vacancy diffusion through the active surface [45,46]. Although the XPS results concerning the vanadium core could be affected by X-ray beam exposure due to ionization effects, the quantification of V 4+ described herein is very similar to that of the reference 27.…”

An efficient robust fluorite CeZrO4−δ oxide catalyst for the eco-benign synthesis of styrene

“…The removal of lattice oxygen is replenished by substituting gaseous molecular oxygen into the lattice which enhances the catalytic activity. 38 Fig. 10 72 hours TOS study of oxidative dehydrogenation of EB to ST over CeZrO 4Àd catalyst (reaction conditions: 550 C, LHSV 3 h À1 with respect to EB, GHSV 2400 h À1 with respect to oxygen, 1 atmosphere pressure, 1 mL catalyst).…”

Local, global, and elementary stoichiometry

“…Sankaranarayanan et al 6 have studied the catalytic oxidation of ethane based on the following set of pictures…”