MultiTRACK and operando Raman-GC study of oxidative dehydrogenation of propane over alumina-supported vanadium oxide catalysts

Abstract

Combined operando Raman-GC and MultiTRACK studies provide new insights into the interaction of propane with a V/alumina catalyst. The Raman-GC analysis showed that the catalyst is essentially in the oxidized state during oxidative dehydrogenation reaction conditions, while stable intermediates and/or carbonaceous deposits are not observed on the catalyst surface. In the absence of oxygen, the catalyst is reduced by propane, and two types of carbonaceous deposits can be observed: one with a more aliphatic character at low temperatures, and one with a graphitic character at higher temperatures, of which the particle size increases as a function of increasing temperature. In agreement with the Raman studies, evidence for carbonaceous deposits was also provided by the MultiTRACK experiments. From CO 2 response profiles of the oxidation of these deposits, it was concluded that increasing temperature of operation and increasing propane/oxygen ratio enhance the amount and stability of the surface carbonaceous species formed. Based on the MultiTRACK studies also the participation of two types of oxygen species in the reaction of propane was evident: a highly reactive super-surface oxygen mainly yielding CO 2 , and a catalytic oxygen, associated with the vanadia phase. In MultiTRACK conditions, the extent of participation of vanadia-associated oxygen increases with reaction temperature and/or the propane/oxygen ratio, enhancing the selectivity of the reaction to propene.

Vanadium Supported on Alumina and/or Zirconia Catalysts for the Selective Transformation of Ethane and Methanol

“…In general, the total H 2 -uptake increases when increasing the V-loading in good agreement with previous results reported by other authors [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. This suggests that all V-atoms are involved in the TPR experiments.…”

“…Al 2 O 3 seem to be one of the most effective support for vanadium in the ODH of ethane [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] as it presents relatively high acidity, which seems to be beneficial in this reaction in contrast with the ODH of propane and n-butane [5][6][7]12]. It seems that the acidity of the support could favor the ethylene desorption from the surface of the catalyst, thus, increasing the selectivity to ethylene [21].…”

“…Supported vanadium oxide catalysts have been considered for many years the most promising catalysts in the ODH of C 2 -C 4 alkanes [4][5][6][7][8][9][10][11][12][13][14], although the nature of the optimal support is different depending on the nature of the alkane fed [5][6][7]14,15]. The catalytic behavior of supported vanadia catalysts can be related to [5][6][7][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]: (i) the nature of V n+ -O species, i.e., coordination, aggregation and oxidation state of V-species; (ii) the redox properties of the catalysts, i.e., the V 5+ /V 4+ ratio in reaction conditions, which are influenced by the presence of promoters and the nature of the metal oxide support; and (iii) the acid-base character of the catalysts (and support), which strongly influences the adsorption of reactants and the desorption of partial oxidation products and finally determines the selectivity to olefins. Depending on the support material and the VOx concentration, supported vanadium oxide can exist as isolated tetrahedral monovanadates, one or two-dimensional polyvanadate domains, or bulk V 2 O 5 crystallites [5][6][7]12,23].…”

Heteroatome steigern die Selektivität der oxidativen Dehydrierung an Nanokohlenstoff

“…Kürzlich konnten wir bereits ¾hnlichkeiten zum Mechanismus der ODH an Vanadiumoxidkatalysatoren aufzeigen. [4,7] Zudem kann es unter ODH-Bedingungen durchaus zur Abscheidung von Kohlenstoff auf der Oberfläche von Metalloxiden kommen, [8] was ein neues Licht auf die katalytische Rolle von Kohlenstoff in der ODH wirft. Ethylbenzol ist bislang das überwiegend verwendete Substrat der kohlenstoffkatalysierten ODH, da die Ausbeute wegen des stabilen konjugierten Elektronensytems des Produkts Styrol hoch ist.…”

Operando XAS and Raman study on the structure of a supported vanadium oxide catalyst during the oxidation of H2S to sulphur

“…More recently, they have been also used in operando conditions in order to clarify the nature of active and selective sites [15][16][17].…”