In situ spectroscopic investigations of MoOx/Fe2O3 catalysts for the selective oxidation of methanol

Brookes, Catherine; Bowker, Michael; Gibson, Emma K.; Gianolio, Diego; Mohammed, Khaled M. H.; Parry, Stephen; Rogers, Scott M.; Silverwood, Ian P.; Wells, Peter P.

doi:10.1039/c5cy01175b

Cited by 24 publications

(24 citation statements)

References 43 publications

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“…In highlighting the use of model MoOx/Fe2O3 catalysts to gain knowledge into the possible surface terminations in bulk FeMo systems, the work of Brookes et al [35] next exploited in situ characterization, specifically to address the reaction mechanisms occurring with methanol. Although widely valued for its efficacy in the reaction, there is a surprising lack of knowledge regarding the catalyst surface layer in Fe2(MoO4)3, and more importantly how it reacts with the incoming methanol reactant under high pressure conditions.…”

Section: Initial Investigations Into the Mechanism And Reaction Site mentioning

confidence: 99%

“…Due to the difficulty in probing the active site under oxidative conditions, an alternative approach has been advocated amongst the group of Brookes et al [35], exploiting their core-shell structures of Mo on Fe2O3 under MeOH/He. Reacting anaerobically enforced a reduction of the surface, which could be analogous to the structural changes occurring momentarily under reaction with MeOH under aerobic conditions.…”

Section: In Situ Investigations Under Meoh/he To Provide Insights Intmentioning

confidence: 99%

“…It could be that Mo (IV) exists temporarily, agreeing with the initial mechanisms of Bowker et al, however, it has not been possible to isolate this species under normal oxidative reaction conditions. Attempts have been made by our group to explore the nature of Mo during the oxidative reaction with methanol [35]. In situ isothermal reaction studies were performed under transmission mode XAFS coupled with mass spectrometry analysis, whilst maintaining the temperature at 250˝C.…”

Section: Initial Investigations Into the Mechanism And Reaction Site mentioning

confidence: 99%

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Catalysts for the Selective Oxidation of Methanol

2016

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Abstract:In industry, one of the main catalysts typically employed for the selective oxidation of methanol to formaldehyde is a multi-component oxide containing both bulk Fe 2 (MoO 4 ) 3 and excess MoO 3 . It is thought that the excess MoO 3 primarily acts to replace any molybdenum lost through sublimation at elevated temperatures, therefore preventing the formation of an unselective Fe 2 O 3 phase. With both oxide phases present however, debate has arisen regarding the active component of the catalyst. Work here highlights how catalyst surfaces are significantly different from bulk structures, a difference crucial for catalyst performance. Specifically, Mo has been isolated at the surface as the active surface species. This leaves the role of the Fe in the catalyst enigmatic, with many theories postulated for its requirement. It has been suggested that the supporting Fe molybdate phase enables lattice oxygen transfer to the surface, to help prevent the selectivity loss which would occur in the resulting oxygen deficit environment. To assess this phenomenon in further detail, anaerobic reaction with methanol has been adopted to evaluate the performance of the catalyst under reducing conditions.

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Section: Initial Investigations Into the Mechanism And Reaction Site mentioning

confidence: 99%

Section: In Situ Investigations Under Meoh/he To Provide Insights Intmentioning

confidence: 99%

Section: Initial Investigations Into the Mechanism And Reaction Site mentioning

confidence: 99%

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Catalysts for the Selective Oxidation of Methanol

2016

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“…In contrast, there is no significant change in the rising edge of the Mo K-edge and, therefore, cannot be used to describe the changes in oxidation state. However, as the concentration of Mo increases, there is a decrease in intensity of the preedge feature indicative of Mo(VI) and usually associated with tetrahedralization but also present in *distorted) octahedral geometries [54,55]. It is therefore suggested that Mo initially populates the surface where it is easily oxidised to Mo(IV) and then infiltrates the bulk at higher concentrations where it adopts Mo(IV), protected from oxidation.…”

Section: Physical Characterizationmentioning

confidence: 99%

Mixed molybdenum and vanadium oxide nanoparticles with excellent high-power performance as Li-ion battery negative electrodes

Bauer

Ashton

Brett

et al. 2019

Electrochimica Acta

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a b s t r a c tSeveral nano-sized mixed molybdenum/vanadium oxide monoclinic solid solutions were synthesised using a continuous hydrothermal flow process and studied with a wide range of physical characterization techniques including X-ray photoelectron spectroscopy, X-ray diffraction, transmission electron microscopy and X-ray absorption spectroscopy. The nanomaterials were tested as anodes for Li-ion batteries in the potential range 0.05e3.00 V vs. Li/Li þ . Samples with nominal formulas of Mo 0.5 V 0.5 O 2 and Mo 0.33 V 0.67 O 2 showed excellent performance, especially at high current rates, due to their highly pseudocapacitive charge storage mechanism. At a specific current of 10 A g À1 , Mo 0.5 V 0.5 O 2 and Mo 0.33 V 0.67 O 2 showed specific capacities of ca. 200 and 170 mAh g À1 , respectively. Mo 0.5 V 0.5 O 2 also showed good cyclability, with a specific capacity of 480 mAh g À1 after 150 cycles at a specific current of 0.5 A g À1 . For cyclic voltammetries conducted at high scan rates, pseudocapacitive charge storage contributed more than 90% to the total charge storage for both samples. The scalability of the synthesis technique and excellent electrochemical performance at high power, make these materials promising as negative electrode active materials for Li-ion batteries.

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“…While there are many examples of designed model catalysts that have been studied and compared with ex situ characterisation [4,74,75], relatively few have been coupled with operando studies. An excellent example of the latter is the work by Bowker and co-workers who designed core-shell MoO x / Fe 2 O 3 catalysts, where single surface monolayers of MoO x , proposed as the active species in conventional Fe 2 (MoO 4 ) 3 , could be studied by XAS without the Mo K edge data being swamped by spectator bulk molybdenum species predominant in Fe 2 (MoO 4 ) 3 catalysts [76,77]. A combination of well-designed operando and transient characterisation experiment coupled with catalyst design is a powerful tool for studying active sites in heterogeneous catalysts.…”

Section: Reactive Materialsmentioning

confidence: 99%

A Perspective on Counting Catalytic Active Sites and Rates of Reaction Using X-Ray Spectroscopy

Kondrat

Bokhoven

2018

Top Catal

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Identification of active sites and phases in heterogeneous catalysts and the understanding of the reaction mechanism remain highly challenging. In most catalysts, the existence of a multitude of surface species, which are dynamic in relation to reaction conditions, presents a challenge of distinguishing those that are involved in the catalytic cycle from those which are spectators. The emergence of the field of single-site catalysts potentially eliminates these issues, although it can be argued that these systems remain dynamic and that multiple speciation, each a candidate for the active site, often remains a consideration. A perspective on how X-ray spectroscopy and characterization tools in general, can be used to correlate the number of active sites and the rate of their formation, in single-site and redox catalyst systems, is presented. The importance of observing proportionality between spectra features and the reaction rate, to differentiate between active sites and spectator species is discussed. Performing characterisation under catalyticly relevant conditions on structures that are demonstrably representative of actual catalysts is essential.

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In situ spectroscopic investigations of MoO_x/Fe₂O₃ catalysts for the selective oxidation of methanol

Abstract: Methoxy adsorbed on MoOx/Fe2O3 surfaces.

Cited by 24 publications

References 43 publications

Catalysts for the Selective Oxidation of Methanol

Catalysts for the Selective Oxidation of Methanol

Mixed molybdenum and vanadium oxide nanoparticles with excellent high-power performance as Li-ion battery negative electrodes

A Perspective on Counting Catalytic Active Sites and Rates of Reaction Using X-Ray Spectroscopy

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