Oxidative dehydrogenation of ethane on diluted or promoted nickel oxide catalysts: Influence of the promoter/diluter

Abstract

Ti-and Nb-containing NiO catalysts have been synthesized by two different preparation methods: i) by precipitation (Me-Ni-O oxides, Me= Nb or Ti), in order to prepare promoted NiO catalysts; and ii) by wet impregnation on TiO2 or NbOx supports, in order to prepare diluted/supported NiO catalysts. The catalysts have been also characterized and tested in the oxidative dehydrogenation of ethane. The catalytic performance of Ti-and Nb-promoted catalysts strongly depends on the composition, although in both cases the optimal one is found at similar Ti or Nb loadings (ca. 90 wt% NiO), showing similar ethylene selectivity in the ODH of ethane (ca. 90% at 10-20% ethane conversion). However, in the case of diluted catalysts, the catalytic behavior of Ti-and Nb-containing catalysts is drastically different. Then, over NiO diluted TiO2 catalyst, the highest selectivity to ethylene (ca. 90% selectivity) is achieved at NiO loading of 20 wt.%. However, over Nb2O5-diluted NiO catalyst, selectivity to ethylene was lower than 70%. A discussion on the characteristics of selective catalysts is done.In this case, the best catalysts must present a low concentration of free NiO and TiO2 or Nb2O5 phases, maximizing the Ni-O-Ti or Ni-O-Nb interaction. Interestingly, this takes place at different NiO loading depending on the preparation method and the nature of promoted/diluter. The low selectivity to ethylene achieved by NiO diluted with Nb2O5 has been related to the low interaction of NiO with the surface of Nb2O5, which hinders the elimination of unselective electrophilic O species.

Understanding structure-activity relationships in highly active La promoted Ni catalysts for CO2 methanation

“…S4 and Table 2). This behavior is due to the merging of the main peak and the satellite I (Sat I), assigned to defects such as Ni 3+ species [61,62],…”

“…2b). These O 1s signals can be deconvoluted into two contributions, giving information about the nucleophilic and electrophilic character of the oxygen species [62,67]. The contribution due to nucleophilic lattice oxygen (i.e.…”

Enhanced NiO Dispersion on a High Surface Area Pillared Heterostructure Covered by Niobium Leads to Optimal Behaviour in the Oxidative Dehydrogenation of Ethane

“…[12][13] NiO system can be considered a paradigmatic example of a host structure in which surface redox properties can be modulated to favour selective pathways in partial oxidation reactions. [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] For example, unmodified NiO acts as a poor catalyst in the ODH of ethane, as it tends to transform ethane mainly into carbon dioxide, showing a low ability for ethylene formation. However, if doped/promoted with a suitable transition metal, [13][14][15][16][17][18][19][20][21][22] or diluted/supported on an appropriate metal oxide, [23][24][25][26] the formation of carbon dioxide can be minimized, thus reaching high selectivity to ethylene.…”

“…Despite this, support/diluted-or dopant/promoter-induced effects, which provoke such a selectivity shift towards ethylene formation, are still unclear. For instance, a decrease in the electrical conductivity, [27,28] the reduction of NiO crystallite size, [29,30] generation of defects, [25,30] , or the elimination of non-selective oxygen species [25,31] have been claimed as common effects that increase ethylene selectivity in the ODH of ethane, for both promoted and supported/diluted NiO catalysts.…”

“…90 %), as suggested previously. [12][13][14][15][16][17][18] On the other hand, supported NiO/Nb2O5 catalysts do not exceed a 60-65 % selectivity to ethylene, [31] due to an ineffective active phase-support interaction. Accordingly, in the present work we have evaluated the possibility to prepare a supported NiO catalyst, with the presence of dispersed niobium species on the support, in order to selectively transform ethane into ethylene by ODH.…”