Molybdenum oxide based partial oxidation catalyst

Abstract

The activation of a Mo9V3W1.2Ox catalyst was investigated in the partial oxidation of acrolein as function of reaction temperature and atmosphere. The activity and selectivity to acrylic acid considerably increased during activation in the acrolein oxidation reaction comparable to the recently reported activation after thermal pretreatment in inert gas. The activation during the catalytic acrolein oxidation, however, proceeds at about 200 K lower temperatures as compared to the inert gas pretreatment. The initial nanocrystalline catalyst structure changed during operation in the acrolein oxidation, as shown by X-ray diffraction (XRD), scanning electron microscopy (SEM), transition electron microscopy and energy dispersive X-ray (EDX) analysis. A (MoVW)5O14-type mixed oxide was found to be the main crystalline phase in the active and selective catalysts. Hence, this (MoVW)5O14 phase crystallizes already during catalysis at the low acrolein oxidation reaction temperatures. The evolution of the catalytic performance is directly related to this low temperature formation of the (MoVW)5O14 phase. It is suggested that this (MoVW)5O14 phase has to be present in a detected, specific ordering state which is vital for optimum selective oxidation properties. In addition, other minority phases were identified by transmission electron microscopy (TEM) in the operating catalyst. The so-called bundle-type, and a new corona-type texture was detected, which show ordering in only one or two dimensions, respectively. These disordered structures are also relevant candidates for active catalyst phases as they are detected during the activation period of the MoVW mixed oxide.

Active Sites for Propane Oxidation: Some Generic Considerations

“…Silica or alumina are thus no optimal supports for partial oxidation catalysts but molybdenum oxide (in the form of the M1 phase) or other reducible mixed oxides with a stable geometric structure [65][66][67][68][69][70][71][72] are suitable choices for reactions involving both C-H activation and oxygen transfer. The in situ analytical results described above and the concept of site isolation preclude, however, the view that a reactive dimer ''antenna site'' may be connected to the bulk of the M1 phase acting as collective electron storage unit.…”

The structural genesis of a complex (MoVW)5O14 oxide during thermal treatments and its redox behavior at elevated temperatures

“…An assignment of chemical and structural specifics to catalytic properties is based upon sterical interpretation rather than on experimental results of physical and chemical characterization [7]. Recently, Mo-V-W mixed oxides consisting of (MoVW) 5 O 14 as the major phase have been studied in the selective oxidation of various substrates including methanol, propylene and acrolein [8][9][10]. In contrast to wellcrystallized Mo 5 O 14 oxide, which shows poor activity in the oxidation of acrolein, an amorphous material equally composed but pretreated under different conditions exhibits much increased activity.…”

“…In contrast to wellcrystallized Mo 5 O 14 oxide, which shows poor activity in the oxidation of acrolein, an amorphous material equally composed but pretreated under different conditions exhibits much increased activity. The latter catalyst undergoes further activation in the course of reaction that is accompanied by an increasing crystallization into the Mo 5 O 15 -type structure [10]. This material remains of considerable stability once operated under steady state conditions.…”

Molybdenum oxide based partial oxidation catalyst

“…It was shown that the actual working catalyst contained a (MoVW) 5 O 14 -type phase as its major component, which either could be preformed by high temperature anneal in inert gas [12], or which directly crystallized during the activation in the catalytic partial oxidation reaction of acrolein [13]. The catalytic performance developed with time on stream parallel to the crystallization of this (MoVW) 5 O 14 -type oxide [13]. Accordingly, this (MoVW) 5 O 14 phase was suggested to play an outstanding role for the partial oxidation of acrolein.…”