Stability of Iron-Molybdate Catalysts for Selective Oxidation of Methanol to Formaldehyde: Influence of Preparation Method

Efficient aqueous molybdenum removal using commercial Douglas fir biochar and its iron oxide hybrids

Molybdenum (Mo) is a naturally-occurring trace element in drinking water. Most commonly, molybdate anions (MoO₄^2-) are in well water and breast milk. In addition, it is used in medical image testing. Recently, the EPA classified Mo as a potential contaminant, as exposure can lead to health effects such as gout, hyperuricemia, and even lung cancer. We have assessed the sorptive removal of aqueous molybdate using Douglas fir biochar (DFBC) and a hybrid DFBC/Fe₃O₄ composite containing chemically-coprecipitated iron oxide (Fe₃O₄). Adsorption was studied at various: pH values, equilibrium times (5 min-24 h), initial Mo concentrations (2.5-1000 mg/L), and temperatures (5, 25, and 40 °C) using batch sorption and fixed-bed column equilibrium methods. Langmuir capacities for DFBC and DFBC/Fe₃O₄ (at pH 3, 2 hrs equilibrium) were within 459.3-487.9 mg/g and 288-572 mg/g, respectively. These adsorbents and their Mo-laden counterparts were characterized by elemental analysis, BET, PZC, SEM, TEM, EDS, XRD, and XPS. MoO₄^2- adsorption on DFBC is thought to be governed primarily via electrostatic attraction. Adsorption by DFBC/Fe₃O₄ is primarily governed by chemisorption onto magnetite surface hydroxyl groups, while electrostatics prevail in the DFBC-exposed phase. Stoichiometric precipitation of iron molybdates triggered by iron dissolution was also considered. The data suggest that DFBC and DFBC/Fe₃O₄ are promising candidates for molybdate sorption.

Modifier Effect in Silica-Supported FePO4 and Fe-Mo-O Catalysts for Propylene Glycol Oxidation

Currently, catalytic processing of biorenewable raw materials into valuable products attracts more and more attention. In the present work, silica-supported FePO₄ and Fe-Mo-O catalysts are prepared, their phase composition, and catalytic properties are studied in the process of selective oxidation of propylene glycol into valuable mono- and bicarbonyl compounds, namely, hydroxyacetone and methylglyoxal. A comparative analysis of the main routes of propylene glycol adsorption with its subsequent oxidative conversion into carbonyl products is carried out. The DFT calculations show that in the presence of adsorbed oxygen atom, the introduction of the phosphate moiety to the Fe-containing site strengthens the alcohol adsorption on the catalyst surface with the formation of the 1,2-propanedioxy (–OCH(CH₃)CH₂O–) intermediate at the active site. The introduction of the molybdenum moiety to the Fe-containing site in the presence of the adsorbed oxygen atom is also energetically favorable, however, the interaction energy is found by 100 kJ/mol higher compared to the case with phosphate moiety that leads to an increase in the propylene glycol conversion while maintaining high selectivity towards C₃ products. The catalytic properties of the synthesized iron-containing catalysts are experimentally compared with those of Ag/SiO₂ sample. The synthesized FePO₄/SiO₂ and Fe-Mo-O/SiO₂ catalysts are not inferior to the silver-containing catalyst and provide ~70% selectivity towards C₃ products, while the main part of propylene glycol is converted into methylglyoxal in contrast to the Ag/SiO₂ catalyst featuring the selective transformation of only the secondary C-OH group in the substrate molecule under the studied conditions with the formation of hydroxyacetone. Thus, supported Fe-Mo-O/SiO₂ catalysts are promising for the selective oxidation of polyatomic alcohols under low-temperature conditions.

Energy Level Alignment at the Cobalt Phosphate/Electrolyte Interface: Intrinsic Stability vs Interfacial Chemical Reactions in 5 V Lithium Ion Batteries

The intrinsic stability of the 5 V LiCoPO₄-LiCo₂P₃O₁₀ thin-film (carbon-free) cathode material coated with MoO₃ thin layer is studied using a comprehensive synchrotron electron spectroscopy in situ approach combined with first-principle calculations. The atomic-molecular level study demonstrates fully reversible electronic properties of the cathode after the first electrochemical cycle. The polyanionic oxide is not involved in chemical reactions with the fluoroethylene-containing liquid electrolyte even when charged to 5.1 V vs Li⁺/Li. The high stability of the cathode is explained on the basis of the developed energy level model. In contrast, the chemical composition of the cathode-electrolyte interface evolves continuously by involving MoO₃ in the decomposition reaction with consequent leaching of oxide from the surface. The proposed mechanisms of chemical reactions are attributed to external electrolyte oxidation via charge transfer from the relevant electron level to the MoO₃ valence band state and internal electrolyte oxidation via proton transfer to the solvents. This study provides a deeper insight into the development of both a doping strategy to enhance the electronic conductivity of high-voltage cathode materials and an efficient surface coating against unfavorable interfacial chemical reactions.

A Review and Experimental Revisit of Alternative Catalysts for Selective Oxidation of Methanol to Formaldehyde

The selective oxidation of methanol to formaldehyde is a growing million-dollar industry, and has been commercial for close to a century. The Formox process, which is the largest production process today, utilizes an iron molybdate catalyst, which is highly selective, but has a short lifetime of 6 months due to volatilization of the active molybdenum oxide. Improvements of the process’s lifetime is, thus, desirable. This paper provides an overview of the efforts reported in the scientific literature to find alternative catalysts for the Formox process and critically assess these alternatives for their industrial potential. The catalysts can be grouped into three main categories: Mo containing, V containing, and those not containing Mo or V. Furthermore, selected interesting catalysts were synthesized, tested for their performance in the title reaction, and the results critically compared with previously published results. Lastly, an outlook on the progress for finding new catalytic materials is provided as well as suggestions for the future focus of Formox catalyst research.

Methanol to Formaldehyde: An Overview of Surface Studies and Performance of an Iron Molybdate Catalyst

Formaldehyde is a primary chemical in the manufacturing of various consumer products. It is synthesized via partial oxidation of methanol using a mixed oxide iron molybdate catalyst (Fe2(MoO4)3–MoO3). This is one of the standard energy-efficient processes. The mixed oxide iron molybdate catalyst is an attractive commercial catalyst for converting methanol to formaldehyde. However, a detailed phase analysis of each oxide phase and a complete understanding of the catalyst formulation and deactivation studies is required. It is crucial to correctly formulate each oxide phase and influence the synthesis methods precisely. A better tradeoff between support and catalyst and oxygen revival on the catalyst surface is vital to enhance the catalyst’s selectivity, stability, and lifetime. This review presents recent advances on iron molybdate’s catalytic behaviour for formaldehyde production—a deep recognition of the catalyst and its critical role in the processes are highlighted. Finally, the conclusion and prospects are presented at the end.

Effect of Ce doping on the structure–activity relationship of MoVOx composite metal oxides

Ce-doped MoVOx with disperse rod-shaped exhibits excellent catalytic performance in selective oxidation of benzyl alcohol.

Effect of Mo Dispersion on the Catalytic Properties and Stability of Mo-Fe Catalysts for the Partial Oxidation of Methanol

Mo-Fe catalysts with different Mo dispersions were synthesized with fast (Cat-FS, 600 r·min^-1) or slow stirring speed (Cat-SS, 30 r·min^-1) by the coprecipitation method. Improving the stirring speed strengthened the mixing of the solution and increased the dispersion of particles in the catalyst, which exhibited favorable activity and selectivity. The byproduct (dimethyl ether (DME)) selectivity increased from 2.3% to 2.8% with Cat-SS, while it remained unchanged with Cat-FS in a stability test. The aggregation of particles and thin Mo-enriched surface layer decreased the catalyst surface area and slowed down the reoxidation of reduced active sites with Cat-SS, leaving more oxygen vacancies which promoted the formation of DME by the nonoxidative channel.

Methanol oxidative dehydrogenation and dehydration on carbon nanotubes: active sites and basic reaction kinetics

In situ active site titration, carbonyl group containing model catalysts, and kinetic analysis have been applied to reveal the nature of oxidized carbon nanotubes catalyzed methanol dehydration and oxidative dehydrogenation reactions.