Catalyseurs Sulfures (Ni)MoW Massiques Et Supportés, Préparés À Partir D'hétéropolyacides Mixtes de Keggin H4SiMonW12-nO40, Pour L'hydrotraitement Des Coupes Lourdes PDF Download
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Author: Aleksandr Kokliukhin
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Refiners have to face the strengthening of environmental requirements for the sulfur content in fuels together the use of heavier crude oil for producing market fuels using hydrotreatment catalytic processes. One of the approaches to improve catalytic activity is the development of bulk and supported ternary NiMoW sulfide catalysts following the recent introduction of industrial mixed bulk NiMoW catalysts NEBULA and Celestia. Previously, for supported alumina catalysts, the use of mixed precursors, H4SiMo1W11O40 and H4SiMo3W9O40 Keggin heteropyacids, has shown a better positive effect on the formation of a highly active mixed MoWS phase than the use of two corresponding monometallic H4SiMo12O40 and H4SiMo12O40 precursors. In this study, a new protocol for the synthesis of mixed Keggin-type H4SiMonW12-nO40 precursors with n = 6 and 9 has been developed. The new compounds were characterized by IR and Raman spectroscopy, as well as single-crystal XRD. Bulk and supported hydrotreating catalysts based on the whole series of H4SiMonW12-nO40 HPAs were synthesized. The influence of the atomic Mo/(Mo+W) ratio on the composition and structure of the active phase and its effect on the catalytic activity of unpromoted alumina supported catalysts in model hydrotreating reactions (hydrodesulfurization of dibenzothiophene and hydrogenation of naphthalene) were studied in detail. It was found that for an atomic Mo/(Mo+W) ratio equal to 0.25 and 0.5, the structure of the active phase under gas-phase sulfidation conditions is a core-shell structure, according to HAADF. A further increase in the molybdenum content up to 0.75 leads to disordering of the active phase structure, which has a negative effect on the catalytic activity. In contrast, for the catalysts obtained from a mixture of monometallic H4SiMo12O40 and H4SiMo12O40 HPAs, the active phase consisted mainly of monometallic MoS2 and WS2 crystallites, regardless of the atomic Mo/(Mo+W) ratio, as a result of which the catalysts showed lower activity compared to the samples prepared from mixed HPAs.The study of the influence of atomic Mo/(Mo+W) ratio for Ni-promoted systems, under the liquid-phase sulfidation in order to be as close as possible to industrial conditions, is also reported. It was shown that the introduction of Ni does not prevent the formation of a mixed MoWS active phase, which was confirmed by HAADF and EXAFS. Moreover, testing in the presence of a nitrogen-containing component made it possible to further study the inhibition on catalytic reactions. It was found that tungsten-rich NiMoW/Al2O3 catalysts are more resistant to the action of nitrogen-containing compounds indicating that the choice of the catalyst composition should be adapted to the composition of the processed feedstock.The use of acid (HF) etching of the alumina support made it possible to obtain from sulfided MonW12-n/Al2O3 samples bulk MoWS catalysts with an active phase concentration of more than 90%. ToF-SIMS and EXAFS showed that the mixed MoWS2 phase is present both in the catalysts synthesized from the mixed HPAs and in the samples obtained from the mixture of two HPAs. However, the concentration of mixed sulfides in the first case is much higher, due to the fact that mixed crystallites have already been formed, whereas in the case of a mixture of two HPAs, a mixed phase is formed as a result of the sintering of particles during re-sulfidation. The high concentration of mixed sulfides made it possible to provide a higher activity of catalysts in model reactions.Replacing alumina with mesostructured silica made it possible to increase the activity of unpromoted MoW catalysts. At the same time, similar values of the degree of sulfidation and dispersion, as well as the results of catalytic tests, seem to indicate that the formation of mixed MoWS2 phase does not occur on this type of supports, which requires additional research to be confirmed.
Author: Aleksandr Kokliukhin
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Refiners have to face the strengthening of environmental requirements for the sulfur content in fuels together the use of heavier crude oil for producing market fuels using hydrotreatment catalytic processes. One of the approaches to improve catalytic activity is the development of bulk and supported ternary NiMoW sulfide catalysts following the recent introduction of industrial mixed bulk NiMoW catalysts NEBULA and Celestia. Previously, for supported alumina catalysts, the use of mixed precursors, H4SiMo1W11O40 and H4SiMo3W9O40 Keggin heteropyacids, has shown a better positive effect on the formation of a highly active mixed MoWS phase than the use of two corresponding monometallic H4SiMo12O40 and H4SiMo12O40 precursors. In this study, a new protocol for the synthesis of mixed Keggin-type H4SiMonW12-nO40 precursors with n = 6 and 9 has been developed. The new compounds were characterized by IR and Raman spectroscopy, as well as single-crystal XRD. Bulk and supported hydrotreating catalysts based on the whole series of H4SiMonW12-nO40 HPAs were synthesized. The influence of the atomic Mo/(Mo+W) ratio on the composition and structure of the active phase and its effect on the catalytic activity of unpromoted alumina supported catalysts in model hydrotreating reactions (hydrodesulfurization of dibenzothiophene and hydrogenation of naphthalene) were studied in detail. It was found that for an atomic Mo/(Mo+W) ratio equal to 0.25 and 0.5, the structure of the active phase under gas-phase sulfidation conditions is a core-shell structure, according to HAADF. A further increase in the molybdenum content up to 0.75 leads to disordering of the active phase structure, which has a negative effect on the catalytic activity. In contrast, for the catalysts obtained from a mixture of monometallic H4SiMo12O40 and H4SiMo12O40 HPAs, the active phase consisted mainly of monometallic MoS2 and WS2 crystallites, regardless of the atomic Mo/(Mo+W) ratio, as a result of which the catalysts showed lower activity compared to the samples prepared from mixed HPAs.The study of the influence of atomic Mo/(Mo+W) ratio for Ni-promoted systems, under the liquid-phase sulfidation in order to be as close as possible to industrial conditions, is also reported. It was shown that the introduction of Ni does not prevent the formation of a mixed MoWS active phase, which was confirmed by HAADF and EXAFS. Moreover, testing in the presence of a nitrogen-containing component made it possible to further study the inhibition on catalytic reactions. It was found that tungsten-rich NiMoW/Al2O3 catalysts are more resistant to the action of nitrogen-containing compounds indicating that the choice of the catalyst composition should be adapted to the composition of the processed feedstock.The use of acid (HF) etching of the alumina support made it possible to obtain from sulfided MonW12-n/Al2O3 samples bulk MoWS catalysts with an active phase concentration of more than 90%. ToF-SIMS and EXAFS showed that the mixed MoWS2 phase is present both in the catalysts synthesized from the mixed HPAs and in the samples obtained from the mixture of two HPAs. However, the concentration of mixed sulfides in the first case is much higher, due to the fact that mixed crystallites have already been formed, whereas in the case of a mixture of two HPAs, a mixed phase is formed as a result of the sintering of particles during re-sulfidation. The high concentration of mixed sulfides made it possible to provide a higher activity of catalysts in model reactions.Replacing alumina with mesostructured silica made it possible to increase the activity of unpromoted MoW catalysts. At the same time, similar values of the degree of sulfidation and dispersion, as well as the results of catalytic tests, seem to indicate that the formation of mixed MoWS2 phase does not occur on this type of supports, which requires additional research to be confirmed.
Author: LARS.. FISCHER
Publisher:
ISBN:
Category :
Languages : fr
Pages : 239
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Book Description
DES CATALYSEURS DE SULFURE DE NI, MO ET NIMO, SUPPORTES SUR ALUMINE ET MODIFIES PAR AJOUT DE 0,8% A 17% POIDS F, ONT ETE EVALUES EN HYDROGENATION DE L'ORTHO-XYLENE SOUS 60 BAR DE PRESSION TOTALE ET 1 BAR DE H 2S. UN FORT EFFET PROMOTEUR DU FLUOR SUR L'ACTIVITE HYDROGENANTE A ETE OBSERVE SUR LES CATALYSEURS NI ET NIMO. LES CARACTERISATIONS DES CATALYSEURS TESTES PAR MICROSCOPIE ELECTRONIQUE ET SPECTROSCOPIE DES PHOTOELECTRONS INDUITS PAR RAYONS X ONT MONTRE QUE LES VARIATIONS EN DISPERSION ET DEGRE DE SULFURATION DE LA PHASE ACTIVE NE SONT PAS ASSEZ IMPORTANTES POUR EXPLIQUER L'AUGMENTATION DE L'ACTIVITE HYDROGENANTE. LES CONDITIONS DU TEST D'HYDROGENATION DE L'ORTHO-XYLENE ONT ETE CHOISIES DE MANIERE A PERMETTRE LA DETERMINATION D'EFFETS ELECTRONIQUES SUR DES CATALYSEURS SULFURES DANS DES CONDITIONS TYPIQUES POUR L'HYDROTRAITEMENT. LE RAPPORT CIS/(CI+TRANS) DES PRODUITS 1,2-DIMETHYL-CYCLOHEXANES EST SENSIBLE A L'ETAT ELECTRONIQUE DES SITES ACTIFS. CECI A ETE VERIFIE PAR L'AJOUT DE L'ELECTRODONNEUR NH 3 ET D'AUTRES EXPERIENCES. D'APRES CE TEST, LE FLUOR AUGMENTE LA DENSITE ELECTRONIQUE DES SITES ACTIFS DANS LES CATALYSEURS NI ET NIMO. EN TRACANT L'ACTIVITE HYDROGENANTE EN FONCTION DE LA DENSITE ELECTRONIQUE, UNE COURBE EN VOLCAN EST OBTENUE DANS LE SYSTEME DES CATALYSEURS SUPPORTES A BASE DE MOS 2 (MO ET NIMO), CE QUI SUGGERE L'EXISTENCE D'UNE DENSITE ELECTRONIQUE OPTIMALE. ELLE SERAIT ATTEINTE AVEC L'INTRODUCTION D'ENVIRON 6% POIDS F SUR UN CATALYSEUR NIMO. LA CARACTERISATION PAR SPECTROSCOPIE INFRAROUGE DE LA VIBRATION DE MOLECULES CO ADSORBES A PERMIS DE CONFIRMER L'EFFET ELECTRODONNEUR DU FLUOR. DES ESSAIS DE FLUORATION D'UN CATALYSEUR MASSIQUE ONT PERMIS D'EXCLURE UNE INTERACTION ENTRE LE FLUOR ET LA PHASE ACTIVE EN ABSENCE DU SUPPORT. IL EST PROPOSE QUE LE FLUOR ELECTRODONNEUR SOIT LOCALISE SUR LA SURFACE DE L'ALUMINE ET AGISSE SUR LE NICKEL VIA UNE INTERACTION VAN DER WAALS.
