TPD/TPR and quantum chemical study of methanol interaction with H3+n PV n Mo12-n O40 heteropolyacids

Serwicka, Ewa M.; Brocławik, Ewa; Brückman, K.; Haber, J.

doi:10.1007/bf00768177

Cited by 10 publications

(9 citation statements)

References 8 publications

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“…In contrast, the model of chemical reactions based on the calculations of the molecular orbitals of the catalyst and reactant suggested in [35,36] represents only an assumption that cannot be directly confirmed by experiment.…”

Section: Numerical Simulation Of the Absorption Spectra Of Hpa Intensmentioning

confidence: 97%

Influence of dehydration effects on the optical spectra of H4PVMo11O40 in the visible and near infrared range: intra- and intercenter optical transitions in the V–Mo cluster

Klokishner

Melsheimer

Ahmad

et al. 2002

Spectrochimica Acta Part A: Molecular and Biomolecular Spectros

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Section: Numerical Simulation Of the Absorption Spectra Of Hpa Intensmentioning

confidence: 97%

Influence of dehydration effects on the optical spectra of H4PVMo11O40 in the visible and near infrared range: intra- and intercenter optical transitions in the V–Mo cluster

Klokishner

Melsheimer

Ahmad

et al. 2002

Spectrochimica Acta Part A: Molecular and Biomolecular Spectros

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“…This is mainly due to the difference in the acidic character and synergism of oxo‐vanadium which greatly favors dehydration and hydrogenation reactions. The vanadium substitution in HPAs enhances nucleophilic reactivity of bridging oxygen atoms in Keggin anion, consequently favoring dehydration pathway …”

Section: Resultsmentioning

confidence: 99%

Catalytic Conversion of Biomass into Hydrocarbons over Noble‐Metal‐Free VO‐Substituted Potassium Salt of Phosphotungstic Acid

et al. 2017

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Bio-fuels emerge as a promising candidate for a sustainable and cheap energy source that can replace diminishing fossil fuels. Among various methods used for the production of biofuel, catalytic hydrodeoxygenation (HDO) is one of the most efficient route due to high conversion efficiency, easy handling and flexibility of using raw biomass. In this context, we present the use of noble-metal-free oxo-vanadium-substituted potassium salt of phosphotungstic acid as a catalyst for HDO of pine sawdust into hydrocarbons and valuable chemicals with a high carbon yield (73.5%) and excellent conversion efficiency (86.2%). The high Brønsted acidity of phosphotungstic acid greatly favors deoxygenation reactions of lignocellulosic com-ponents. Moreover, the synergistic effect between kegginanion, potassium and vanadium entities supports fast multielectron redox transformations and much improves thermal stability. The cellulosic components are selectively converted into pentanes and hexanes. The lignin fraction of biomass is converted into phenolic compounds. It is worth mentioning that raw biomass is directly utilized as obtained without pretreatment, separation and hydrolysis processes in comparison with the existing approaches, thus saving tremendous amount of energy and reducing the cost for large scale production.[a] Dr.

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“…Similar stability was confirmed for other compositions of Keggin structures; it is consistent with the strong interaction between pyridine rings and protons in Keggin structures detected by temperature-programmed desorption in this study, and from infrared spectra and thermal desorption data in previous studies. [8,9] These stable organic-inorganic composites represent a novel class of materials that have significant implications for selectivity control in bifunctional redox-acid catalysis. Pyridine has been used to measure the number of available acid sites in fresh samples (not during catalytic reactions), [8][9][10] but we have found no previous studies describing the intentional use of organic bases as selectivity modifiers for these types of materials.…”

Section: Methodsmentioning

confidence: 99%

“…[8,9] These stable organic-inorganic composites represent a novel class of materials that have significant implications for selectivity control in bifunctional redox-acid catalysis. Pyridine has been used to measure the number of available acid sites in fresh samples (not during catalytic reactions), [8][9][10] but we have found no previous studies describing the intentional use of organic bases as selectivity modifiers for these types of materials. Pyridine-KU complexes have been previously synthesized in efforts to form secondary Keggin structures, for which subsequent removal of pyridine during thermal treatments and before reaction may lead to specific pore morphologies or reduced addenda atoms.…”

Section: Methodsmentioning

confidence: 99%

Site Titration with Organic Bases During Catalysis: Selectivity Modifier and Structural Probe in Methanol Oxidation on Keggin Clusters

2003

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Catalytic reactions often require several types of sites with distinct functions, and the relative abundance of these sites influences the rate and selectivity of desired reactions. Heteropolyacid clusters with Keggin structures, which contain acid and redox functions, [1,2] have recently emerged as interesting catalysts for organic reactions involving bifunctional pathways.We recently discovered a selective one-step synthesis of dimethoxymethane (CH 3 OCH 2 OCH 3 , DMM, methylal) by oxidation of methanol at low temperatures (453-493 K) on unsupported and SiO 2 -supported H 3+n PV n Mo 12Àn O 40 (n = 0-4) Keggin clusters.[3] The yields and selectivities (based on the absence of dimethyl ether) of DMM resemble those obtained using supported ReO x catalysts, the only catalysts that enable the formation of DMM in substantial yields.[4] Redox and Brønsted acid sites are required for DMM synthesis, and the reaction involves oxidative dehydrogenation of CH 3 OH to formaldehyde (HCHO), acid-catalyzed acetalization of CH 3 OH/HCHO mixtures, and condensation of hemiacetal or methoxymethanol intermediates (formed in acetalization reactions) [5,6] with CH 3 OH to form DMM. Brönsted acidity is required to complete the synthesis of DMM, but reaction rates are predominately controlled by the initial formation of HCHO on redox sites, the density and reactivity of which were varied in our studies by changing the dispersion and V/Mo ratio of the Keggin structures, with consequent changes in the rates of DMM synthesis. These compositional changes led to concurrent changes in the number of acid sites, because of the stoichiometry required to balance the charge. DMM selectivity is decreased by side reactions involving CH 3 OH dehydration. These reactions are catalyzed by strongly acidic protons in H 3+n PV n Mo 12Àn O 40 and lead to the undesired formation of dimethyl ether (DME). The latter product ultimately converts into HCHO and DMM products, and can even re-form CH 3 OH, but forms DMM more slowly than CH 3 OH.[3] Thus, the formation of DME through these side reactions necessitates longer residence times to achieve high yields of DMM from CH 3 OH.We report here the selective titration of protons with organic bases to control the densities of acid sites in Keggin clusters and to measure their dispersion; in both cases we do this during the catalytic reaction, a requirement imposed by the dynamic changes in accessibility that arise from reactions of polar molecules on Keggin clusters. [1,2] In this manner we are able to measure turnover rates (per exposed Keggin unit; KU) and to control the redox and acid properties independently for a given composition of Keggin cluster. This approach has led to unprecedented DMM selectivities (> 80 %) and to a family of stable organic-inorganic composites that provide effective bifunctional catalysts for broad classes of redox-acid bifunctional reactions.The dispersion of Keggin structures was measured by titration of Brønsted acid sites with a sterically hindered pyridine (2,6-di-tert-butylpyri...

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TPD/TPR and quantum chemical study of methanol interaction with H3+n PV n Mo12-n O40 heteropolyacids

Cited by 10 publications

References 8 publications

Influence of dehydration effects on the optical spectra of H4PVMo11O40 in the visible and near infrared range: intra- and intercenter optical transitions in the V–Mo cluster

Influence of dehydration effects on the optical spectra of H4PVMo11O40 in the visible and near infrared range: intra- and intercenter optical transitions in the V–Mo cluster

Catalytic Conversion of Biomass into Hydrocarbons over Noble‐Metal‐Free VO‐Substituted Potassium Salt of Phosphotungstic Acid

Site Titration with Organic Bases During Catalysis: Selectivity Modifier and Structural Probe in Methanol Oxidation on Keggin Clusters

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