Modeling of the molybdenum loss in iron molybdate catalyst pellets for selective oxidation of methanol to formaldehyde

Abstract

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Alkali Earth Metal Molybdates as Catalysts for the Selective Oxidation of Methanol to Formaldehyde—Selectivity, Activity, and Stability

“…From the literature [49,54], it seemed the MoO 3 evaporation from the industrial catalyst pellets (ring shaped cylinders with outer diameter = 4.55 mm, hole diameter = 1.70 mm, and length = 4.00 mm) was a diffusion limited process, as it took much longer time for the excess MoO 3 to disappear from pellets than the sieve fraction used here (150-250 µm), under similar conditions. Additionally, a reactor model indicated that reducing MoO 3 evaporation only for the catalyst layer near the inlet might to a large extent solve the problem of increasing pressure drop [55].…”

Operando XAS/XRD and Raman Spectroscopic Study of Structural Changes of the Iron Molybdate Catalyst during Selective Oxidation of Methanol

“…[15,16] The re-oxidation to Fe 2 (MoO 4 ) 3 was slow and only partly reversible, possibly caused by the lack of excess MoO 3 . [20] Inspection by scanning electron microscopy (SEM) showed that the volatilization of MoO 3 occurred from the outer pellet surface and formed a depletion layer where all MoO 3 had evaporated and a pellet core where the composition is like the fresh catalyst. Our group has studied the deactivation and degradation of a FeMo catalyst at about 400°C, with Mo/Fe = 2.0 for up to 600 h on stream using a catalyst sieve fraction of 150 to 250 μm.…”

Modeling of molybdenum transport and pressure drop increase in fixed bed reactors used for selective oxidation of methanol to formaldehyde using iron molybdate catalysts

“…As mentioned above the volatile Mo-species are observed to deposit in the void space between the catalyst pellets downstream in the reactor [14], [16]- [19]. In our group, we have experimentally studied and modeled the Mo loss from a single iron molybdate/molybdenum oxide pellet under well-defined reaction conditions [21]. It was observed that the Mo loss was strongly dependent on the MeOH concentration corresponding to a reaction order of 1.5, and was inhibited by H 2 O.…”

“…In this work, we present an implementation of our previous single pellet model [21] into a reactor model and show simulation results for the vaporization and downstream deposition of MoO 3 and the development of the pressure drop over time. A study on catalyst modifications to minimize the pressure drop increase is also presented.…”