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Alexis T Bell - One of the best experts on this subject based on the ideXlab platform.
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mechanism and kinetics of propane Dehydrogenation and cracking over ga h mfi prepared via vapor phase exchange of h mfi with gacl3
Journal of the American Chemical Society, 2019Co-Authors: Neelay M Phadke, Erum Mansoor, Matthieu Bondil, Martin Headgordon, Alexis T BellAbstract:In this study, the mechanism and kinetics of C3H8 Dehydrogenation and cracking are examined over Ga/H-MFI catalysts prepared via vapor-phase exchange of H-MFI with GaCl3. The present study demonstrates that [GaH]2+ cations are the active centers for C3H8 Dehydrogenation and cracking, independent of the Ga/Al ratio. For identical reaction conditions, [GaH]2+ cations in Ga/H-MFI exhibit a turnover frequency for C3H8 Dehydrogenation that is 2 orders of magnitude higher and for C3H8 cracking, that is 1 order of magnitude higher than the corresponding turnover frequencies over H-MFI. C3H8 Dehydrogenation and cracking exhibit first-order kinetics with respect to C3H8 over H-MFI, but both reactions exhibit first-order kinetics over Ga/H-MFI only at very low C3H8 partial pressures and zero-order kinetics at higher C3H8 partial pressures. H2 inhibits both reactions over Ga/H-MFI. It is also found that the ratio of the rate of Dehydrogenation to the rate of cracking over Ga/H-MFI is independent of C3H8 and H2 parti...
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novel pt mg in al o catalysts for ethane and propane Dehydrogenation
Journal of Catalysis, 2011Co-Authors: Georges Siddiqi, William Collins Vining, Alexis T BellAbstract:Catalysts for the Dehydrogenation of light alkanes were prepared by dispersing Pt on the surface of a calcined hydrotalcite-like support containing indium, Mg(In)(Al)O. Upon reduction in H2 at temperatures above 673 K, bimetallic particles of PtIn are observed by TEM, which have an average diameter of 1 nm. Analysis of Pt LIII-edge extended X-ray absorption fine structure (EXAFS) data shows that the In content of the bimetallic particles increases with increasing bulk In/Pt ratio and reduction temperature. Pt LIII-edge X-ray absorption near edge structure (XANES) indicates that an increasing donation of electronic charge from In to Pt occurs with increasing In content in the PtIn particles. The activity and selectivity of the Pt/Mg(In)(Al)O catalysts for ethane and propane Dehydrogenation reactions are strongly dependent on the bulk In/Pt ratio. For both reactants, maximum activity was achieved for a bulk In/Pt ratio of 0.48, and at this In/Pt ratio, the selectivity to alkene was nearly 100%. Coke deposition was observed after catalyst use for either ethane or propane Dehydrogenation, and it was observed that the alloying of Pt with In greatly reduced the amount of coke deposited. Characterization of the deposit by Raman spectroscopy indicates that the coke is present as highly disordered graphite particles <30 nm in diameter. While the amount of coke deposited during ethane and propane Dehydrogenation are comparable, the effects on activity are dependent on reactant composition. Coke deposition had no effect on ethane Dehydrogenation activity, but caused a loss in propane Dehydrogenation activity. This difference is attributed to the greater ease with which coke produced on the surface of PtIn nanoparticles migrates to the support during ethane Dehydrogenation versus propane Dehydrogenation.
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catalyst performance of novel pt mg ga al o catalysts for alkane Dehydrogenation
Journal of Catalysis, 2010Co-Authors: Georges Siddiqi, Vladimir Galvita, Alexis T BellAbstract:The Dehydrogenation of ethane and propane using a Pt catalyst supported on a novel Mg(Ga)(Al)O mixed oxide support was investigated. Catalyst performance is strongly dependent on Ga content in the support, a peak in activity for both ethane and propane Dehydrogenation occurs at Ga/Pt = 1.4–5.4, and selectivity is a monotonic function of Ga/Pt, reaching nearly 100% at Ga/Pt = 5.4. The addition of hydrogen to the feed resulted in a peak in activity with respect to H2/alkane. The increase in Dehydrogenation rate with H2 addition is attributed to H-atom-assisted Dehydrogenation of alkyl species formed upon dissociative adsorption of the reactant alkane. Beyond the peak in activity with H2 addition, a further increase in H2 feed concentration contribute to alkene hydrogenation, thereby reducing the net rate of Dehydrogenation. Hydrogen addition to the feed, however, had relatively little effect on alkene selectivity, which remained near 100%. The presence of Ga also suppressed coke formation. Interestingly, less coke was formed during propane Dehydrogenation than ethane Dehydrogenation, and no correlation was found between coke formation and catalyst deactivation. Thus, the extent of deactivation was lower for ethane than propane Dehydrogenation, whereas the amount of coke deposited was higher in the former case. Since the amount of carbon deposited as coke is higher than the amount of exposed Pt, it is concluded that most of the coke resides on the support, and that only a small amount resides on the Pt particles. The higher level of deactivation seen during propane versus ethane Dehydrogenation is attributed to a higher coverage of Pt by coke precursors derived from propane than ethane.
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kinetic isotopic effects in oxidative Dehydrogenation of propane on vanadium oxide catalysts
Journal of Catalysis, 2000Co-Authors: Alexis T Bell, Enrique Iglesia, Kaidong ChenAbstract:Abstract Kinetic isotopic effects (KIEs) for oxidative Dehydrogenation of propane were measured on 10 wt% V 2 O 5 /ZrO 2 . Normal KIEs were obtained using CH 3 CH 2 CH 3 and CD 3 CD 2 CD 3 as reactants for primary Dehydrogenation (2.8) and combustion (1.9) of propane and for secondary combustion of propene (2.6), suggesting that in all cases C–H bond dissociation is a kinetically relevant step. CH 3 CH 2 CH 3 and CH 3 CD 2 CH 3 reactants led to normal KIEs for Dehydrogenation (2.7) and combustion (1.8) of propane, but to a very small KIE (1.1) for propene combustion. These results show that the methylene C–H bond is activated in the rate-determining steps for propane Dehydrogenation and combustion reactions. The rate-determining step in secondary propene combustion involves the allylic C–H bond. In each reaction, the weakest C–H bond in the reactant is cleaved in the initial C–H bond activation step. The measured propane oxidative Dehydrogenation KIEs are in agreement with theoretical estimates using a sequence of elementary steps, reaction rate expression, and transition state theory. The much smaller KIE for propane oxidative Dehydrogenation (2.8) than the maximum KIE (6) expected for propane thermal Dehydrogenation indicates the participation of lattice oxygen. The different KIE values for propane primary Dehydrogenation and combustion suggest that these two reactions involve different lattice oxygen sites.
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Synthesis of Butyronitrile via Ammonolysis of Butylalcohol and Dehydrogenation of Butylamine over Mo2N
Journal of Catalysis, 1993Co-Authors: H. Abe, Alexis T BellAbstract:Investigations were carried out of the synthesis of butyronitrile via the ammonolysis of butylalcohol and the Dehydrogenation of butylamine over Mo[sub 2]N. At 573 K butyronitrile is produced with virtually 100% yielded by both reactions. The ammonolysis of butylalcohol proceeds via Dehydrogenation of the butylalcohol to form butyraldehyde, which then reacts with ammonia to produce butylimine. Butyronitrile is formed by butylimine Dehydrogenation. The formation of butyronitrile from butylamine occurs via the stepwise Dehydrogenation of the amine. The presence of ammonia in the gas phase suppresses the hydrogenolysis of either butylalcohol or butylamine. 11 refs., 8 figs., 2 tabs.
Umit B Demirci - One of the best experts on this subject based on the ideXlab platform.
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key study on the potential of hydrazine bisborane for solid and liquid state chemical hydrogen storage
Inorganic Chemistry, 2015Co-Authors: Sergii Pylypko, Eddy Petit, Marc Cretin, Philippe Miele, Fabrice Salles, Umit B DemirciAbstract:Hydrazine bisborane N2H4(BH3)2 (HBB; 16.8 wt %) recently re-emerged as a potential hydrogen storage material. However, such potential is controversial: HBB was seen as a hazardous compound up to 2010, but now it would be suitable for hydrogen storage. In this context, we focused on fundamentals of HBB because they are missing in the literature and should help to shed light on its effective potential while taking into consideration any risk. Experimental/computational methods were used to get a complete characterization data sheet, including, e.g., XRD, NMR, FTIR, Raman, TGA, and DSC. From the reported results and discussion, it is concluded that HBB has potential in the field of chemical hydrogen storage given that both thermolytic and hydrolytic Dehydrogenations were analyzed. In solid-state chemical hydrogen storage, it cannot be used in the pristine state (risk of explosion during Dehydrogenation) but can be used for the synthesis of derivatives with improved Dehydrogenation properties. In liquid-state...
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Key Study on the Potential of Hydrazine Bisborane for Solid- and Liquid-State Chemical Hydrogen Storage
Inorganic Chemistry, 2015Co-Authors: Sergii Pylypko, Eddy Petit, Pascal G. Yot, Marc Cretin, Philippe Miele, Fabrice Salles, Umit B DemirciAbstract:Hydrazine bisborane N2H4(BH3)2 (HBB; 16.8 wt %) recently re-emerged as a potential hydrogen storage material. However, such potential is controversial: HBB was seen as a hazardous compound up to 2010, but now it would be suitable for hydrogen storage. In this context, we focused on fundamentals of HBB because they are missing in the literature and should help to shed light on its effective potential while taking into consideration any risk. Experimental/computational methods were used to get a complete characterization data sheet, including, e.g., XRD, NMR, FTIR, Raman, TGA, and DSC. From the reported results and discussion, it is concluded that HBB has potential in the field of chemical hydrogen storage given that both thermolytic and hydrolytic Dehydrogenations were analyzed. In solid-state chemical hydrogen storage, it cannot be used in the pristine state (risk of explosion during Dehydrogenation) but can be used for the synthesis of derivatives with improved Dehydrogenation properties. In liquid-state chemical hydrogen storage, it can be studied for room-temperature Dehydrogenation, but this requires the development of an active and selective metal-based catalyst. HBB is a thus a candidate for chemical hydrogen storage.
Fahim Karimi - One of the best experts on this subject based on the ideXlab platform.
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in situ formation of tib2 nanoparticles for enhanced Dehydrogenation hydrogenation reaction kinetics of libh4 mgh2 as a reversible solid state hydrogen storage composite system
Journal of Physical Chemistry C, 2018Co-Authors: Fahim Karimi, Maria Victoria Castro Riglos, Antonio Santoru, Armin Hoell, Vikram Singh Raghuwanshi, Chiara Milanese, Nils Bergemann, Claudio Pistidda, Pau Nolis, M D BaroAbstract:To enhance the Dehydrogenation/rehydrogenation kinetic behavior of the LiBH4–MgH2 composite system, TiF4 is used as an additive. The effect of this additive on the hydride composite system has been...
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in situ formation of tib2 nanoparticles for enhanced Dehydrogenation hydrogenation reaction kinetics of libh4 mgh2 as a reversible solid state hydrogen storage composite system
Journal of Physical Chemistry C, 2018Co-Authors: Fahim Karimi, Maria Victoria Castro Riglos, Antonio Santoru, Armin Hoell, Vikram Singh Raghuwanshi, Chiara Milanese, Nils Bergemann, Claudio Pistidda, Pau Nolis, M D BaroAbstract:To enhance the Dehydrogenation/rehydrogenation kinetic behavior of the LiBH4–MgH2 composite system, TiF4 is used as an additive. The effect of this additive on the hydride composite system has been studied by means of laboratory and advanced synchrotron techniques. Investigations on the synthesis and mechanism upon hydrogen interaction show that the addition of TiF4 to the LiBH4–MgH2 composite system during the milling procedure leads to the in situ formation of well-distributed nanosized TiB2 particles. These TiB2 nanoparticles act as nucleation agents for the formation of MgB2 upon Dehydrogenation process of the hydride composite system. The effect of TiB2 nanoparticles is maintained upon cycling.
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structural analysis of calcium reactive hydride composite for solid state hydrogen storage
Journal of Applied Crystallography, 2014Co-Authors: Fahim Karimi, Armin Hoell, Vikram Singh Raghuwanshi, Claudio Pistidda, Thomas Klassen, Martin Dornheim, Klaus P Pranzas, Ulla Vainio, Edmund Welter, A SchreyerAbstract:Owing to a theoretical hydrogen storage capacity of 10.5 wt% H2, Ca(BH4)2+MgH2, the so-called calcium reactive hydride composite (Ca-RHC), has a great potential as a hydrogen storage material. However, its Dehydrogenation temperature (∼623 K) is too high for any mobile applications. By addition of 10 mol% of NbF5 into Ca(BH4)2+MgH2, a decrease of the Dehydrogenation onset temperature by ∼120 K is observed. In order to understand the reasons behind this desorption temperature decrement two sets of samples [Ca(BH4)2+MgH2 and Ca(BH4)2+MgH2+0.1NbF5] in different hydrogenation states, were prepared. The structural investigation of the above mentioned sets of samples by means of volumetric measurements, anomalous small-angle X-ray scattering (ASAXS) and X-ray absorption spectroscopy (XAS) is reported here. The XAS results show that after the milling procedure NbB2 is formed and remains stable upon further de/rehydrogenation cycling. The results of Nb ASAXS point to nanometric spherical NbB2 particles distributed in the hydride matrix, with a mean diameter of ∼10 nm. Results from Ca ASAXS indicate Ca-containing nanostructures in the Ca-RHC+0.1NbF5 samples to be ∼50% finer compared to those without additive. Thus, a higher reaction surface area and shorter diffusion paths for the constituents are concluded to be important contributions to the catalytic effect of an NbF5 additive on the hydrogen sorption kinetics of the Ca(BH4)2+MgH2 composite system.
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nanoconfined 2libh4 mgh2 for reversible hydrogen storages reaction mechanisms kinetics and thermodynamics
International Journal of Hydrogen Energy, 2013Co-Authors: Rapee Gosalawitutke, Fahim Karimi, Chiara Milanese, Thomas K Nielsen, Ivan Saldan, Klaus Pranzas, Torben R Jensen, Amedeo Marini, Thomas Klassen, Martin DornheimAbstract:Abstract Samples of nanoconfined Reactive Hydride Composites in resorcinol–formaldehyde aerogel scaffolds (RF–CAS) are prepared by (i) direct melt infiltration of bulk 2LiBH4–MgH2; and (ii) MgH2 impregnation and LiBH4 melt infiltration. The reaction mechanisms, kinetics and thermodynamics of the systems are concluded. Activation energy (EA) and Dehydrogenation enthalpies of LiBH4 and MgH2 ( Δ H des , MgH 2 + Δ H des , LiBH 4 ) of nanoconfined 2LiBH4–MgH2 are in this work of interest. The hydrogen sorption reactions in both nanoconfined samples are reversible as shown by the recovering of LiBH4 and MgH2 after rehydrogenation. The titration results show the remarkable improvement in desorption kinetics of nanoconfined samples over the bulk material, such as more than 90% of overall hydrogen storage capacity is obtained within 2 h from the nanoconfined samples during the 1st Dehydrogenation, while that of bulk material needs more than 16 h. The activation energy of the composites decreases by 27–170 kJ/mol (ΔEA) due to nanoconfinement. For thermodynamics, ( Δ H des , MgH 2 + Δ H des , LiBH 4 ) calculated from DSC results of the nanoconfined samples are in the range of 41–46 kJ/mol H2.
Zhigang Zak Fang - One of the best experts on this subject based on the ideXlab platform.
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reaction mechanisms in the li3alh6 libh4 and al libh4 systems for reversible hydrogen storage part 2 solid state nmr studies
Journal of Physical Chemistry C, 2011Co-Authors: Young Choi, Hong Yong Sohn, Zhigang Zak Fang, Jun Lu, R C Bowman, Sonjong HwangAbstract:In Part 1, the promising hydrogen storage properties of the combined systems of Li3AlH6/LiBH4 and Al/LiBH4, exhibiting the favorable formation of AlB2 during Dehydrogenation, were presented based on TGA and XRD analyses. The present Part 2 describes the characterization of the intermediate and final products of the Dehydrogenation and rehydrogenation of the above systems by multinuclear solid-state NMR characterization. This work has also verified that the presence of Al resulted in the re-formation of LiBH4 occurring at a much lower temperature and H2 pressure, under which conditions the Dehydrogenation product from LiBH4 alone does not show any degree of rehydrogenation. NMR studies mainly identified various reaction intermediates for LiBH4 Dehydrogenation/rehydrogenation reactions. Unlike the XRD studies, the AlB2 formation, in particular, could not be unambiguously confirmed by NMR. 27Al NMR showed that aluminum was mainly involved in various Li—Al alloy formations. The catalytic role of Al in the LiB...
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hydrogen storage properties of nanosized mgh2 0 1tih2 prepared by ultrahigh energy high pressure milling
Journal of the American Chemical Society, 2009Co-Authors: Jun Lu, Zhigang Zak Fang, Young Joon Choi, H Y Sohn, Ewa RonnebroAbstract:Magnesium hydride (MgH2) is an attractive candidate for solid-state hydrogen storage applications. To improve the kinetics and thermodynamic properties of MgH2 during Dehydrogenation−rehydrogenation cycles, a nanostructured MgH2−0.1TiH2 material system prepared by ultrahigh-energy−high-pressure mechanical milling was investigated. High-resolution transmission electron microscope (TEM) and scanning TEM analysis showed that the grain size of the milled MgH2−0.1TiH2 powder is approximately 5−10 nm with uniform distributions of TiH2 among MgH2 particles. Pressure−composition-temperature (PCT) analysis demonstrated that both the nanosize and the addition of TiH2 contributed to the significant improvement of the kinetics of Dehydrogenation and hydrogenation compared to commercial MgH2. More importantly, PCT cycle analysis demonstrated that the MgH2−0.1TiH2 material system showed excellent cycle stability. The results also showed that the ΔH value for the Dehydrogenation of nanostructured MgH2−0.1TiH2 is signifi...
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hydrogen storage properties of the mg ti h system prepared by high energy high pressure reactive milling
Journal of Power Sources, 2008Co-Authors: Young Choi, H Y Sohn, Zhigang Zak FangAbstract:Abstract Magnesium-based alloys are among the promising materials for hydrogen storage and fuel cell applications due to their high hydrogen content. In the present work, we investigated the hydrogen release/uptake properties of the Mg–Ti–H system. Samples were prepared from the mixtures of MgH 2 and TiH 2 in molar ratios of 7:1 and 4:1 using a high-energy-high-pressure (HEHP) mechanical ball-milling method under 13.8 MPa hydrogen pressure. Thermogravimetric analysis (TGA) showed that a relatively large amount of hydrogen (5.91 and 4.82 wt.%, respectively, for the above two samples) was released between 126 and 313 °C while temperature was increased at a heating rate of 5 °C min −1 under an argon flow. The onset Dehydrogenation temperature of these mixtures, which is 126 °C, is much lower than that of MgH 2 alone, which is 381 °C. The activation energy of Dehydrogenation was 71 kJ mol −1 , which is much smaller than that of as-received MgH 2 (153 kJ mol −1 ) or as-milled MgH 2 (96 kJ mol −1 ). Furthermore, the hydrogen capacity and the Dehydrogenation temperature remained largely unchanged over five Dehydrogenation and rehydrogenation cycles.
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a new li al n h system for reversible hydrogen storage
Journal of Physical Chemistry B, 2006Co-Authors: Jun Lu, Zhigang Zak Fang, Hong Yong SohnAbstract:Complex metal hydrides are considered as a class of candidate materials for hydrogen storage. Lithium-based complex hydrides including lithium alanates (LiAlH4 and Li3AlH6) are among the most promising materials owing to its high hydrogen content. In the present work, we investigated Dehydrogenation/rehydrogenation reactions of a combined system of Li3AlH6 and LiNH2. Thermogravimetric analysis (TGA) of Li3AlH6/3LiNH2/4 wt % TiCl3−1/3AlCl3 mixtures indicated that a large amount of hydrogen (∼7.1 wt %) can be released between 150 °C and 300 °C under a heating rate of 5 °C/min in two Dehydrogenation reaction steps. The results also show that the Dehydrogenation reaction of the new material system is nearly 100% reversible under 2000 psi pressure hydrogen at 300 °C. Further, a short-cycle experiment has demonstrated that the new combined material system of alanates and amides can maintain its hydrogen storage capacity upon cycling of the Dehydrogenation/rehydrogenation reactions.
Sergii Pylypko - One of the best experts on this subject based on the ideXlab platform.
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key study on the potential of hydrazine bisborane for solid and liquid state chemical hydrogen storage
Inorganic Chemistry, 2015Co-Authors: Sergii Pylypko, Eddy Petit, Marc Cretin, Philippe Miele, Fabrice Salles, Umit B DemirciAbstract:Hydrazine bisborane N2H4(BH3)2 (HBB; 16.8 wt %) recently re-emerged as a potential hydrogen storage material. However, such potential is controversial: HBB was seen as a hazardous compound up to 2010, but now it would be suitable for hydrogen storage. In this context, we focused on fundamentals of HBB because they are missing in the literature and should help to shed light on its effective potential while taking into consideration any risk. Experimental/computational methods were used to get a complete characterization data sheet, including, e.g., XRD, NMR, FTIR, Raman, TGA, and DSC. From the reported results and discussion, it is concluded that HBB has potential in the field of chemical hydrogen storage given that both thermolytic and hydrolytic Dehydrogenations were analyzed. In solid-state chemical hydrogen storage, it cannot be used in the pristine state (risk of explosion during Dehydrogenation) but can be used for the synthesis of derivatives with improved Dehydrogenation properties. In liquid-state...
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Key Study on the Potential of Hydrazine Bisborane for Solid- and Liquid-State Chemical Hydrogen Storage
Inorganic Chemistry, 2015Co-Authors: Sergii Pylypko, Eddy Petit, Pascal G. Yot, Marc Cretin, Philippe Miele, Fabrice Salles, Umit B DemirciAbstract:Hydrazine bisborane N2H4(BH3)2 (HBB; 16.8 wt %) recently re-emerged as a potential hydrogen storage material. However, such potential is controversial: HBB was seen as a hazardous compound up to 2010, but now it would be suitable for hydrogen storage. In this context, we focused on fundamentals of HBB because they are missing in the literature and should help to shed light on its effective potential while taking into consideration any risk. Experimental/computational methods were used to get a complete characterization data sheet, including, e.g., XRD, NMR, FTIR, Raman, TGA, and DSC. From the reported results and discussion, it is concluded that HBB has potential in the field of chemical hydrogen storage given that both thermolytic and hydrolytic Dehydrogenations were analyzed. In solid-state chemical hydrogen storage, it cannot be used in the pristine state (risk of explosion during Dehydrogenation) but can be used for the synthesis of derivatives with improved Dehydrogenation properties. In liquid-state chemical hydrogen storage, it can be studied for room-temperature Dehydrogenation, but this requires the development of an active and selective metal-based catalyst. HBB is a thus a candidate for chemical hydrogen storage.