Study by electrical conductivity measurements of semiconductive and redox properties of M-doped NiO (M = Li, Mg, Al, Ga, Ti, Nb) catalysts for the oxidative dehydrogenation of ethane

Abstract

Pure and M-doped nickel oxides with M = Li, Mg, Al, Ga, Ti, Nb, catalysts for the oxidative dehydrogenation of ethane into ethylene, were characterized by in situ electrical conductivity measurements. Their electrical conductivity was studied as a function of temperature and oxygen partial pressure and was followed with time during sequential exposures to air, an ethane-air mixture (reaction mixture) and pure ethane under conditions similar to those of catalysis. All the materials appeared to be p-type semiconductors under air with positive holes as the main charge carriers and their electrical conductivity decreased in the following order: Li-NiO > NiO > Mg-NiO > Nb-NiO > Ga-NiO > Al-NiO > Ti-NiO. All the catalysts remained p-type semiconductors in the reaction mixture at 400 °C. Correlations between the p-type semiconductivity and the catalytic properties have been evidenced. The reaction mechanism involves surface lattice O(-) species and can be assimilated to a Mars and van Krevelen mechanism.

A study by electrical conductivity measurements of the semiconductive and redox properties of Nb-doped NiO catalysts in correlation with the oxidative dehydrogenation of ethane

“…It can be observed that the activation energy of conduction is significantly lower for all the oxides beyond the Néel temperature. At the same time, for both temperature ranges considered, the E c values were higher for all Nb(x)NiO samples compared to the NiO reference, as already observed for NiO doped with higher valent cations 26,36 and presents only small differences between the Nb(x)NiO systems. pure NiO at this temperature.…”

“…11,12 A useful and highly sensitive technique to characterize the electronic and redox properties of oxidation catalysts is the electrical conductivity measurement, 13 a large number of papers having been dedicated to this subject in the last decade. [14][15][16][17][18][19][20][21][22][23][24][25][26] Numerous previous studies have correlated the electrical conductivity of the oxide materials with their catalytic performance in ODH reactions of ethane into ethylene, 19,[26][27][28] propane into propene, [29][30][31] n-butane into butenes and butadiene 32,33 and isobutane into isobutene. 17,20 NiO is a p-type semiconducting oxide containing an excess of lattice oxygen anions associated with the existence of positive holes as main charge carriers.…”

“…In this case electrons are released in the valence band of the oxide resulting in the decrease of the positive holes concentration and thus in the decrease of the electrical conductivity. We have already studied the electrical and catalytic properties of M-doped NiO (M = Li, Mg, Al, Ga, Nb, Ti) in ethane ODH 26 and were able to explain their catalytic behavior and to elucidate the differences in their catalytic performance based on the differences in the conductivity of the materials when exposed to air, ethane and ethane-air reaction mixture.…”

A self-redox pure-phase M1 MoVNbTeO /CeO2 nanocomposite as a highly active catalyst for oxidative dehydrogenation of ethane

“…Supported catalysts (NiO-based [8,9] and VO x -based [10][11][12] metal oxide catalysts) and unsupported catalysts (NiWO x -based [13], NiNbO x -based [14][15][16][17], NiSnO x -based [18], and MoVO x -based metal mixed oxide catalysts [19,20]) both show high activity in the ODHE reaction at a relatively low temperature (<500°C). Among all the catalytic systems above, a mixed metal oxide catalyst, MoVNbTeO x , is one of the most outstanding catalysts for ODHE [21][22][23][24][25][26][27][28][29][30][31][32].…”

Heterogeneous Partial (amm)Oxidation and Oxidative Dehydrogenation Catalysis on Mixed Metal Oxides

“…This phenomenon was assigned to electron transfer enhancement played by Nb, leading to easier activation of the C-H bond of ethane (see above Section 4.2 & Figure 11 from [67]). Other promoters such as Zr, which acts as a Lewis acid, but also Mg, Li, Ga, Ti, Ta, [96] or alumina have also been proposed for NiO catalyst to increase ethylene yield.…”