Oxidative dehydrogenation of ethane and propane : How far from commercial implementation?

Supported V2O5/Ce1–xTixO2 (3, 5, and 7 wt % V; x = 0, 0.1, 0.3, 0.5, 1) and bare supports have been tested in the selective catalytic reduction (SCR) of NO by NH3 at different gas hourly space velocities (GHSVs) and were comprehensively characterized using XRD, pseudo in situ XPS, and UV–vis DRS as well as EPR and DRIFTS in in situ and operando mode. The best V/Ce1–xTixO2 (x = 0.3, 0.5) catalysts showed almost 100% NO conversion and N2 selectivity already at 190 °C with a GHSV value of 70000 h–1, which belongs to the best performances observed so far in low-temperature NH3-SCR of NO. The corresponding bare supports still converted around 80% to N2 under the same conditions. On bare supports, SCR proceeds via a Langmuir–Hinshelwood mechanism comprising the reaction of adsorbed surface nitrates with adsorbed NH3. On V/Ce1–xTixO2, nitrate formation is not possible, and an Eley–Rideal mechanism is working in which gaseous NO reacts with adsorbed NH3 and NH4+. Lewis and Bronsted acid sites, though adsorption o...

Efficient VOx/Ce1–xTixO2 Catalysts for Low-Temperature NH3-SCR: Reaction Mechanism and Active Sites Assessed by in Situ/Operando Spectroscopy

Comparative study of propane dehydrogenation over V-, Cr-, and Pt-based catalysts: Time on-stream behavior and origins of deactivation

The ordered hexagonal mesoporous pure silica SBA-15 has been used as a support for preparing highly dispersed V-containing catalysts. VOx/SBA-15 samples with different V loading (1.26–5.54 wt.%) have been prepared by impregnation with an aqueous solution of NH4VO3, characterized by N2 adsorption, UV-Vis spectroscopy, and H2-TPR and then evaluated for the partial oxidation of methane to formaldehyde with oxygen. For vanadium coverages below the theoretical monolayer capacity (corresponding to ca. 4 wt.% V) the SBA-15 surface was predominantly covered by monomeric and low oligomeric vanadium oxide species, while at higher vanadium coverages agglomerated vanadium entities and even some small amounts of microcrystalline V2O5 were also formed. The conversion of methane (at constant temperature and GHSV) passed a maximum at a vanadium loading of 3.85 wt.%, while the maximum of activity typically occurs at lower V contents (1–2 wt.%) in amorphous vanadia-silica catalysts. This feature can be related with the much higher surface area of the mesoporous support, which allows the monolayer capacity to be reached at higher loading than in amorphous silica. The influence of the main reaction parameters (temperature, GHSV, CH4:O2 ratio) on the productivity of formaldehyde was studied. A maximum space–time yield (STY) of formaldehyde of about 2.4 kg kg−1 h−1 was obtained in this work for the most active VOx/SBA-15 catalyst (3.85 wt.% V) at 618 °C, GHSV=417,000 l (N) kg−1 h−1, and CH4:O2 molar ratio of 8:1. This value of STYHCHO is significantly higher than the maximum STY (ca. 1.3 kg kg−1 h−1) reported for VOx/SiO2, and comparable to that recently reported for VOx/MCM-41 (ca. 2.2 kg kg−1 h−1), thus confirming the promising use of high surface area mesoporous supports for the POM reaction on vanadia based catalysts.

Catalytic performance of mesoporous VOx/SBA-15 catalysts for the partial oxidation of methane to formaldehyde

V-containing materials have been proposed as active and selective catalysts in the selective oxidative transformation of C2–C4 alkanes to the corresponding olefins, oxygenates and nitriles. Although vanadium ions are generally assumed as the active sites in the oxidative activation of short chain alkanes, the coordination, the oxidation state and the environment of V atoms strongly influence both the catalytic activity and the nature of the reaction products. A comparative study on the catalytic behaviour of V-containing catalysts, i.e. metal vanadates, supported vanadium oxides, V-containing microporous/mesoporous materials and multicomponent bulk Mo–V–Te(Sb)–Nb mixed metal oxides, on the alkane oxidation is presented. The influence of the structure (including the V-coordination and V-environment) and the physico-chemical properties (especially redox and acid–base characteristics) of the catalysts on their behaviour in the selective oxidation of paraffins and alkenes is discussed.

The selective oxidative activation of light alkanes. From supported vanadia to multicomponent bulk V-containing catalysts

The Structure of Active Sites in Me–V–O Catalysts (Me = Mg, Zn, Pb) and Its Influence on the Catalytic Performance in the Oxidative Dehydrogenation (ODH) of Propane

VOx species supported on mesoporous Al2O3, SBA-15 and MCM-48 materials have been studied by simultaneous in situ-EPR/UV-vis/on line-GC measurements and tested as catalysts for the ODH of propane. Highest propene yields can be obtained with catalysts of very high surface area in which active V sites have a mean valence state close to +4, are highly dispersed and preferably tetrahedrally coordinated by oxygen. Coke deposits formed at high reaction temperature and propane concentrations do not deactivate the catalysts but enhance the propene selectivity by covering acidic sites of the support.

Highly dispersed VOx species on mesoporous supports: Promising catalysts for the oxidative dehydrogenation (ODH) of propane

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The Structure of Active Sites in Me–V–O Catalysts (Me = Mg, Zn, Pb) and Its Influence on the Catalytic Performance in the Oxidative Dehydrogenation (ODH) of Propane

Highly dispersed VOx species on mesoporous supports: Promising catalysts for the oxidative dehydrogenation (ODH) of propane