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Ivan V Kozhevnikov - One of the best experts on this subject based on the ideXlab platform.

  • Deoxygenation of Ethers and Esters over Bifunctional Pt–Heteropoly Acid Catalyst in the Gas Phase
    2016
    Co-Authors: Khadijah Alharbi, Walaa Alharbi, Elena F Kozhevnikova, Ivan V Kozhevnikov
    Abstract:

    Deoxygenation and decomposition of ethers and esters, including anisole, diisopropyl ether (DPE), and ethyl propanoate (EP), was investigated using bifunctional metal–acid catalysis at a gas–solid Interface in the presence and absence of hydrogen. The bifunctional catalysts studied comprised Pt, Ru, Ni, and Cu as the metal components and Cs2.5H0.5PW12O40 (CsPW), an acidic Cs salt of Keggin-type heteropoly acid (HPA) H3PW12O40, as the acid component, with the main focus on Pt–CsPW catalyst. It was found that bifunctional metal–acid catalysis in the presence of H2 is more efficient for ether and ester deoxygenation than the corresponding monofunctional metal and acid catalysis and that metal- and acid-catalyzed pathways play different roles in these reactions. With Pt-CsPW, hydrodeoxygenation of anisole, a model for the deoxygenation of lignin, occurred with 100% yield of cyclohexane under very mild conditions (60–100 °C and 1 bar of H2). This catalyst had the highest activity in anisole deoxygenation for a gas-phase catalyst system reported so far. The catalyst activity decreased in the order of metals: Pt ≫ Ru > Ni > Cu. For HPA-catalyzed DPE and EP decomposition, relationships between the turnover reaction rate (turnover frequency) and the HPA acid strength were found, which can be used to predict the activity of acid catalysts in these reactions

  • dehydration of methanol to dimethyl ether over heteropoly acid catalysts the relationship between reaction rate and catalyst acid strength
    ACS Catalysis, 2015
    Co-Authors: Walaa Alharbi, Elena F Kozhevnikova, Ivan V Kozhevnikov
    Abstract:

    Dehydration of methanol to dimethyl ether (DME) was studied at a gas/solid Interface over a wide range of bulk and supported Bronsted acid catalysts based on tungsten Keggin heteropoly acids (HPA) and compared with the reaction over HZSM-5 zeolites (Si/Al = 10–120). Turnover rates for these catalysts were measured under zero-order reaction conditions. The HPA catalysts were demonstrated to have much higher catalytic activities than the HZSM-5 zeolites. A good correlation between the turnover rates and catalyst acid strengths, represented by the initial enthalpies of ammonia adsorption, was established. This correlation holds for the HPA and HZSM-5 catalysts studied, which indicates that the methanol-to-DME dehydration with both HPA and HZSM-5 catalysts occurs via the same (or similar) mechanism and the turnover rate of methanol dehydration for both catalysts is primarily determined by the strength of catalyst acid sites, regardless of the catalyst pore geometry.

  • dehydration of ethanol over heteropoly acid catalysts in the gas phase
    Journal of Catalysis, 2014
    Co-Authors: Walaa Alharbi, Elena F Kozhevnikova, Esther Brown, Ivan V Kozhevnikov
    Abstract:

    Abstract Dehydration of ethanol was studied at a gas–solid Interface over a wide range of solid Bronsted acid catalysts based on Keggin-type heteropoly acids (HPAs) in a continuous flow fixed-bed reactor in the temperature range of 90–220 °C focussing on the formation of diethyl ether (DEE). The catalysts included H 3 PW 12 O 40 (HPW) and H 4 SiW 12 O 40 (HSiW) supported on SiO 2 , TiO 2 , Nb 2 O 5 and ZrO 2 with sub-monolayer HPA coverage, as well as bulk acidic Cs salts of HPW (Cs 2.5 H 0.5 PW 12 O 40 and Cs 2.25 H 0.75 PW 12 O 40 ) and the corresponding core–shell materials with the same total composition (15%HPW/Cs 3 PW 12 O 40 and 25%HPW/Cs 3 PW 12 O 40 , respectively) comprising HPW supported on the neutral salt Cs 3 PW 12 O 40 . The ethanol-to-DEE reaction was found to be zero order in ethanol in the range of 1.5–10 kPa ethanol partial pressure. The acid strength of catalysts was characterised by ammonia adsorption microcalorimetry. A fairly good correlation between the catalyst activity (turnover frequency) and the catalyst acid strength (initial enthalpy of ammonia adsorption) was established, which demonstrates that Bronsted acid sites play important role in ethanol-to-DEE dehydration over HPA catalysts. The acid strength and the catalytic activity of core–shell catalysts HPW/Cs 3 PW 12 O 40 did not exceed those of the corresponding bulk Cs salts of HPW with the same total composition, which contradicts the literature claims of the superiority of the core–shell HPA catalysts.

  • solid acid catalysts based on h3pw12o40 heteropoly acid acid and catalytic properties at a gas solid Interface
    Journal of Catalysis, 2010
    Co-Authors: Ali Alsalme, Elena F Kozhevnikova, Paul V Wiper, Yaroslav Z Khimyak, Ivan V Kozhevnikov
    Abstract:

    Abstract Solid acid catalysts prepared by supporting 15 wt%H 3 PW 12 O 40 heteropoly acid (HPA) on TiO 2 , ZrO 2 and Nb 2 O 5 with a sub-monolayer HPA coverage were characterised at a gas–solid Interface, regarding their acid properties and chemical structure of HPA on the catalyst surface and compared to “standard” HPA catalysts such as bulk and silica-supported H 3 PW 12 O 40 and Cs 2.5 H 0.5 PW 12 O 40 . In contrast to the parent acid, H 3 PW 12 O 40 , possessing strong Bronsted acid sites, the catalysts supported on TiO 2 , ZrO 2 and Nb 2 O 5 have both Bronsted and Lewis acid sites, with the latter mainly originating from the oxide support. The strength of acid sites in these catalysts is weaker than that in H 3 PW 12 O 40 and Cs 2.5 H 0.5 PW 12 O 40 . The catalytic activity (turnover frequency) in gas-phase isopropanol dehydration decreases in the order: H 3 PW 12 O 40  > Cs 2.5 H 0.5 PW 12 O 40  > 15%H 3 PW 12 O 40 /SiO 2  > 15%H 3 PW 12 O 40 /TiO 2  > 15%H 3 PW 12 O 40 /Nb 2 O 5  > 15%H 3 PW 12 O 40 /ZrO 2 , which is in line with the acid strength as determined by NH 3 adsorption calorimetry. Ammonia adsorption calorimetry, 31 P{ 1 H} MAS NMR and FTIR indicate increasing interaction between support and HPA in the following order of supports: SiO 2 2 2 O 5 2 .

Elena F Kozhevnikova - One of the best experts on this subject based on the ideXlab platform.

  • Deoxygenation of Ethers and Esters over Bifunctional Pt–Heteropoly Acid Catalyst in the Gas Phase
    2016
    Co-Authors: Khadijah Alharbi, Walaa Alharbi, Elena F Kozhevnikova, Ivan V Kozhevnikov
    Abstract:

    Deoxygenation and decomposition of ethers and esters, including anisole, diisopropyl ether (DPE), and ethyl propanoate (EP), was investigated using bifunctional metal–acid catalysis at a gas–solid Interface in the presence and absence of hydrogen. The bifunctional catalysts studied comprised Pt, Ru, Ni, and Cu as the metal components and Cs2.5H0.5PW12O40 (CsPW), an acidic Cs salt of Keggin-type heteropoly acid (HPA) H3PW12O40, as the acid component, with the main focus on Pt–CsPW catalyst. It was found that bifunctional metal–acid catalysis in the presence of H2 is more efficient for ether and ester deoxygenation than the corresponding monofunctional metal and acid catalysis and that metal- and acid-catalyzed pathways play different roles in these reactions. With Pt-CsPW, hydrodeoxygenation of anisole, a model for the deoxygenation of lignin, occurred with 100% yield of cyclohexane under very mild conditions (60–100 °C and 1 bar of H2). This catalyst had the highest activity in anisole deoxygenation for a gas-phase catalyst system reported so far. The catalyst activity decreased in the order of metals: Pt ≫ Ru > Ni > Cu. For HPA-catalyzed DPE and EP decomposition, relationships between the turnover reaction rate (turnover frequency) and the HPA acid strength were found, which can be used to predict the activity of acid catalysts in these reactions

  • dehydration of methanol to dimethyl ether over heteropoly acid catalysts the relationship between reaction rate and catalyst acid strength
    ACS Catalysis, 2015
    Co-Authors: Walaa Alharbi, Elena F Kozhevnikova, Ivan V Kozhevnikov
    Abstract:

    Dehydration of methanol to dimethyl ether (DME) was studied at a gas/solid Interface over a wide range of bulk and supported Bronsted acid catalysts based on tungsten Keggin heteropoly acids (HPA) and compared with the reaction over HZSM-5 zeolites (Si/Al = 10–120). Turnover rates for these catalysts were measured under zero-order reaction conditions. The HPA catalysts were demonstrated to have much higher catalytic activities than the HZSM-5 zeolites. A good correlation between the turnover rates and catalyst acid strengths, represented by the initial enthalpies of ammonia adsorption, was established. This correlation holds for the HPA and HZSM-5 catalysts studied, which indicates that the methanol-to-DME dehydration with both HPA and HZSM-5 catalysts occurs via the same (or similar) mechanism and the turnover rate of methanol dehydration for both catalysts is primarily determined by the strength of catalyst acid sites, regardless of the catalyst pore geometry.

  • dehydration of ethanol over heteropoly acid catalysts in the gas phase
    Journal of Catalysis, 2014
    Co-Authors: Walaa Alharbi, Elena F Kozhevnikova, Esther Brown, Ivan V Kozhevnikov
    Abstract:

    Abstract Dehydration of ethanol was studied at a gas–solid Interface over a wide range of solid Bronsted acid catalysts based on Keggin-type heteropoly acids (HPAs) in a continuous flow fixed-bed reactor in the temperature range of 90–220 °C focussing on the formation of diethyl ether (DEE). The catalysts included H 3 PW 12 O 40 (HPW) and H 4 SiW 12 O 40 (HSiW) supported on SiO 2 , TiO 2 , Nb 2 O 5 and ZrO 2 with sub-monolayer HPA coverage, as well as bulk acidic Cs salts of HPW (Cs 2.5 H 0.5 PW 12 O 40 and Cs 2.25 H 0.75 PW 12 O 40 ) and the corresponding core–shell materials with the same total composition (15%HPW/Cs 3 PW 12 O 40 and 25%HPW/Cs 3 PW 12 O 40 , respectively) comprising HPW supported on the neutral salt Cs 3 PW 12 O 40 . The ethanol-to-DEE reaction was found to be zero order in ethanol in the range of 1.5–10 kPa ethanol partial pressure. The acid strength of catalysts was characterised by ammonia adsorption microcalorimetry. A fairly good correlation between the catalyst activity (turnover frequency) and the catalyst acid strength (initial enthalpy of ammonia adsorption) was established, which demonstrates that Bronsted acid sites play important role in ethanol-to-DEE dehydration over HPA catalysts. The acid strength and the catalytic activity of core–shell catalysts HPW/Cs 3 PW 12 O 40 did not exceed those of the corresponding bulk Cs salts of HPW with the same total composition, which contradicts the literature claims of the superiority of the core–shell HPA catalysts.

  • solid acid catalysts based on h3pw12o40 heteropoly acid acid and catalytic properties at a gas solid Interface
    Journal of Catalysis, 2010
    Co-Authors: Ali Alsalme, Elena F Kozhevnikova, Paul V Wiper, Yaroslav Z Khimyak, Ivan V Kozhevnikov
    Abstract:

    Abstract Solid acid catalysts prepared by supporting 15 wt%H 3 PW 12 O 40 heteropoly acid (HPA) on TiO 2 , ZrO 2 and Nb 2 O 5 with a sub-monolayer HPA coverage were characterised at a gas–solid Interface, regarding their acid properties and chemical structure of HPA on the catalyst surface and compared to “standard” HPA catalysts such as bulk and silica-supported H 3 PW 12 O 40 and Cs 2.5 H 0.5 PW 12 O 40 . In contrast to the parent acid, H 3 PW 12 O 40 , possessing strong Bronsted acid sites, the catalysts supported on TiO 2 , ZrO 2 and Nb 2 O 5 have both Bronsted and Lewis acid sites, with the latter mainly originating from the oxide support. The strength of acid sites in these catalysts is weaker than that in H 3 PW 12 O 40 and Cs 2.5 H 0.5 PW 12 O 40 . The catalytic activity (turnover frequency) in gas-phase isopropanol dehydration decreases in the order: H 3 PW 12 O 40  > Cs 2.5 H 0.5 PW 12 O 40  > 15%H 3 PW 12 O 40 /SiO 2  > 15%H 3 PW 12 O 40 /TiO 2  > 15%H 3 PW 12 O 40 /Nb 2 O 5  > 15%H 3 PW 12 O 40 /ZrO 2 , which is in line with the acid strength as determined by NH 3 adsorption calorimetry. Ammonia adsorption calorimetry, 31 P{ 1 H} MAS NMR and FTIR indicate increasing interaction between support and HPA in the following order of supports: SiO 2 2 2 O 5 2 .

Walaa Alharbi - One of the best experts on this subject based on the ideXlab platform.

  • Deoxygenation of Ethers and Esters over Bifunctional Pt–Heteropoly Acid Catalyst in the Gas Phase
    2016
    Co-Authors: Khadijah Alharbi, Walaa Alharbi, Elena F Kozhevnikova, Ivan V Kozhevnikov
    Abstract:

    Deoxygenation and decomposition of ethers and esters, including anisole, diisopropyl ether (DPE), and ethyl propanoate (EP), was investigated using bifunctional metal–acid catalysis at a gas–solid Interface in the presence and absence of hydrogen. The bifunctional catalysts studied comprised Pt, Ru, Ni, and Cu as the metal components and Cs2.5H0.5PW12O40 (CsPW), an acidic Cs salt of Keggin-type heteropoly acid (HPA) H3PW12O40, as the acid component, with the main focus on Pt–CsPW catalyst. It was found that bifunctional metal–acid catalysis in the presence of H2 is more efficient for ether and ester deoxygenation than the corresponding monofunctional metal and acid catalysis and that metal- and acid-catalyzed pathways play different roles in these reactions. With Pt-CsPW, hydrodeoxygenation of anisole, a model for the deoxygenation of lignin, occurred with 100% yield of cyclohexane under very mild conditions (60–100 °C and 1 bar of H2). This catalyst had the highest activity in anisole deoxygenation for a gas-phase catalyst system reported so far. The catalyst activity decreased in the order of metals: Pt ≫ Ru > Ni > Cu. For HPA-catalyzed DPE and EP decomposition, relationships between the turnover reaction rate (turnover frequency) and the HPA acid strength were found, which can be used to predict the activity of acid catalysts in these reactions

  • dehydration of methanol to dimethyl ether over heteropoly acid catalysts the relationship between reaction rate and catalyst acid strength
    ACS Catalysis, 2015
    Co-Authors: Walaa Alharbi, Elena F Kozhevnikova, Ivan V Kozhevnikov
    Abstract:

    Dehydration of methanol to dimethyl ether (DME) was studied at a gas/solid Interface over a wide range of bulk and supported Bronsted acid catalysts based on tungsten Keggin heteropoly acids (HPA) and compared with the reaction over HZSM-5 zeolites (Si/Al = 10–120). Turnover rates for these catalysts were measured under zero-order reaction conditions. The HPA catalysts were demonstrated to have much higher catalytic activities than the HZSM-5 zeolites. A good correlation between the turnover rates and catalyst acid strengths, represented by the initial enthalpies of ammonia adsorption, was established. This correlation holds for the HPA and HZSM-5 catalysts studied, which indicates that the methanol-to-DME dehydration with both HPA and HZSM-5 catalysts occurs via the same (or similar) mechanism and the turnover rate of methanol dehydration for both catalysts is primarily determined by the strength of catalyst acid sites, regardless of the catalyst pore geometry.

  • dehydration of ethanol over heteropoly acid catalysts in the gas phase
    Journal of Catalysis, 2014
    Co-Authors: Walaa Alharbi, Elena F Kozhevnikova, Esther Brown, Ivan V Kozhevnikov
    Abstract:

    Abstract Dehydration of ethanol was studied at a gas–solid Interface over a wide range of solid Bronsted acid catalysts based on Keggin-type heteropoly acids (HPAs) in a continuous flow fixed-bed reactor in the temperature range of 90–220 °C focussing on the formation of diethyl ether (DEE). The catalysts included H 3 PW 12 O 40 (HPW) and H 4 SiW 12 O 40 (HSiW) supported on SiO 2 , TiO 2 , Nb 2 O 5 and ZrO 2 with sub-monolayer HPA coverage, as well as bulk acidic Cs salts of HPW (Cs 2.5 H 0.5 PW 12 O 40 and Cs 2.25 H 0.75 PW 12 O 40 ) and the corresponding core–shell materials with the same total composition (15%HPW/Cs 3 PW 12 O 40 and 25%HPW/Cs 3 PW 12 O 40 , respectively) comprising HPW supported on the neutral salt Cs 3 PW 12 O 40 . The ethanol-to-DEE reaction was found to be zero order in ethanol in the range of 1.5–10 kPa ethanol partial pressure. The acid strength of catalysts was characterised by ammonia adsorption microcalorimetry. A fairly good correlation between the catalyst activity (turnover frequency) and the catalyst acid strength (initial enthalpy of ammonia adsorption) was established, which demonstrates that Bronsted acid sites play important role in ethanol-to-DEE dehydration over HPA catalysts. The acid strength and the catalytic activity of core–shell catalysts HPW/Cs 3 PW 12 O 40 did not exceed those of the corresponding bulk Cs salts of HPW with the same total composition, which contradicts the literature claims of the superiority of the core–shell HPA catalysts.

John R. Morris - One of the best experts on this subject based on the ideXlab platform.

  • Correlated Multimodal Approach Reveals Key Details of Nerve-Agent Decomposition by Single-Site Zr-Based Polyoxometalates.
    The Journal of Physical Chemistry Letters, 2019
    Co-Authors: Yiyao Tian, Anna M. Plonka, Amani M. Ebrahim, Robert M. Palomino, Sanjaya D. Senanayake, Alex Balboa, Wesley O. Gordon, Diego Troya, Djamaladdin G. Musaev, John R. Morris
    Abstract:

    Development of technologies for protection against chemical warfare agents (CWAs) is critically important. Recently, polyoxometalates have attracted attention as potential catalysts for nerve-agent decomposition. Improvement of their effectiveness in real operating conditions requires an atomic-level understanding of CWA decomposition at the gas–solid Interface. We investigated decomposition of the nerve agent Sarin and its simulant, dimethyl chlorophosphate (DMCP), by zirconium polytungstate. Using a multimodal approach, we showed that upon DMCP and Sarin exposure the dimeric tungstate undergoes monomerization, making coordinatively unsaturated Zr(IV) centers available, which activate nucleophilic hydrolysis. Further, DMCP is shown to be a good model system of reduced toxicity for studies of CWA deactivation at the gas–solid Interface.

  • Correlated Multimodal Approach Reveals Key Details of Nerve-Agent Decomposition by Single-Site Zr-Based Polyoxometalates
    2019
    Co-Authors: Yiyao Tian, Anna M. Plonka, Amani M. Ebrahim, Robert M. Palomino, Sanjaya D. Senanayake, Alex Balboa, Wesley O. Gordon, Diego Troya, Djamaladdin G. Musaev, John R. Morris
    Abstract:

    Development of technologies for protection against chemical warfare agents (CWAs) is critically important. Recently, polyoxometalates have attracted attention as potential catalysts for nerve-agent decomposition. Improvement of their effectiveness in real operating conditions requires an atomic-level understanding of CWA decomposition at the gas–solid Interface. We investigated decomposition of the nerve agent Sarin and its simulant, dimethyl chlorophosphate (DMCP), by zirconium polytungstate. Using a multimodal approach, we showed that upon DMCP and Sarin exposure the dimeric tungstate undergoes monomerization, making coordinatively unsaturated Zr­(IV) centers available, which activate nucleophilic hydrolysis. Further, DMCP is shown to be a good model system of reduced toxicity for studies of CWA deactivation at the gas–solid Interface

Felix Sharipov - One of the best experts on this subject based on the ideXlab platform.

  • data on the velocity slip and temperature jump on a gas solid Interface
    Journal of Physical and Chemical Reference Data, 2011
    Co-Authors: Felix Sharipov
    Abstract:

    The present review is dedicated to the velocity slip and temperature jump coefficients applied to modeling of gas flows. Such coefficients are used when a moderate gas rarefaction must be taken into account. In this case, calculations of gas flows can be performed on the basis of continuum mechanics equations applying the velocity slip and temperature jump boundary conditions. Thus, the velocity slip and temperature jump coefficients have the same importance in gas dynamics as the transport coefficients such as viscosity, thermal conductivity, and diffusion coefficients. A critical analysis of theoretical and experimental data on the slip and jump coefficients available in the open literature is presented in an accessible form so that it can be easily understandable for nonspecialists in rarefied gas dynamics. The most reliable results are selected and tabulated. The results cover a single gas with the complete and noncomplete accommodation on a solid surface, gaseous mixtures, and polyatomic gases. Many ...

  • data on the velocity slip and temperature jump on a gas solid Interface
    Journal of Physical and Chemical Reference Data, 2011
    Co-Authors: Felix Sharipov
    Abstract:

    The present review is dedicated to the velocity slip and temperature jump coefficients applied to modeling of gas flows. Such coefficients are used when a moderate gas rarefaction must be taken into account. In this case, calculations of gas flows can be performed on the basis of continuum mechanics equations applying the velocity slip and temperature jump boundary conditions. Thus, the velocity slip and temperature jump coefficients have the same importance in gas dynamics as the transport coefficients such as viscosity, thermal conductivity, and diffusion coefficients. A critical analysis of theoretical and experimental data on the slip and jump coefficients available in the open literature is presented in an accessible form so that it can be easily understandable for nonspecialists in rarefied gas dynamics. The most reliable results are selected and tabulated. The results cover a single gas with the complete and noncomplete accommodation on a solid surface, gaseous mixtures, and polyatomic gases. Many examples of applications of the slip and jump boundary conditions are given. The review will be useful as a reference for mathematicians, physicists, and engineers dealing with flows of moderately rarefied gases.