51915-19-6Relevant articles and documents
Mechanistic Insights into Catalytic Ethanol Steam Reforming Using Isotope-Labeled Reactants
Crowley, Stephen,Castaldi, Marco J.
supporting information, p. 10650 - 10655 (2016/09/03)
The low-temperature ethanol steam reforming (ESR) reaction mechanism over a supported Rh/Pt catalyst has been investigated using isotope-labeled EtOH and H2O. Through strategic isotope labeling, all nonhydrogen atoms were distinct from one another, and allowed an unprecedented level of understanding of the dominant reaction pathways. All combinations of isotope- and non-isotope-labeled atoms were detected in the products, thus there are multiple pathways involved in H2, CO, CO2, CH4, C2H4, and C2H6product formation. Both the recombination of C species on the surface of the catalyst and preservation of the C?C bond within ethanol are responsible for C2product formation. Ethylene is not detected until conversion drops below 100 % at t=1.25 h. Also, quantitatively, 57 % of the observed ethylene is formed directly through ethanol dehydration. Finally there is clear evidence to show that oxygen in the SiO2-ZrO2support constitutes 10 % of the CO formed during the reaction.
The influence of catalyst acid strength on the methanol to hydrocarbons (MTH) reaction
Westg?rd Erichsen, Marius,Svelle, Stian,Olsbye, Unni
, p. 216 - 223 (2013/09/02)
The methanol to hydrocarbons (MTH) reaction was studied over two isostructural zeotype catalysts of different acid strength, H-SAPO-5 and H-SSZ-24. Conversion of methanol alone was performed at 350-450 C and WHSV = 0.31-2.48 h-1. The product selectivities of the two catalysts were compared at similar conversion. The strongly acidic H-SSZ-24 was found to be more selective towards aromatic products and C2-C3 hydrocarbons as compared to the moderately acidic H-SAPO-5, which produced more non-aromatic C4+ hydrocarbons. Co-reactions of 13CH 3OH and benzene at 250-300 C with low conversion of both reactants revealed that both catalysts produced ethene and propene from polymethylbenzenes via a paring mechanism. However, this reaction proceeded more readily in H-SSZ-24 than in H-SAPO-5. Furthermore, isobutene formation was found to be mainly associated with aromatic intermediates in H-SSZ-24, whereas isobutene produced over H-SAPO-5 was mainly formed via alkene intermediates. Overall, the results obtained in this study suggest that a lower acid strength promotes an alkene-mediated MTH reaction mechanism.
Cationic zirconium hydrides supported by an nnnn-type macrocyclic ligand: Synthesis, structure, and reactivity
Kulinna, Heiko,Spaniol, Thomas P.,Maron, Laurent,Okuda, Jun
, p. 12462 - 12472 (2013/01/15)
An air- and light-sensitive, but thermally stable tris[(trimethylsilyl) methyl]zirconium complex containing an NNNN-type macrocyclic ligand [Zr(Me 3TACD)(CH2SiMe3)3] (1; Me 3TACD = Me3[12]aneN4: 1,4,7-trimethyl-1,4,7,10- tetraazacyclododecane) was prepared by reacting [Zr(CH2SiMe 3)4] with (Me3TACD)H. Reaction of the zirconium tris(alkyl) 1 with a Lewis or Bronsted acid gave a dialkyl cation with a weakly coordinating anion [Zr(Me3TACD)(CH2SiMe 3)2][A] [A = Al{OC(CF3)3} 4 (2a), B{3,5-C6H3(CF3) 2}4 (2b), B(3,5-C6H3Cl 2)4 (2c), and BPh4) (2d)]. Hydrogenolysis of 2a-2c resulted in the formation of the dinuclear tetrahydride dication [{Zr(Me3TACD)(μ-H)2}2][A]2 (3a-3c). Compounds 1-3 were characterized by multinuclear NMR spectroscopy, and the solid-state structures of 1, 2c, and 3b were established by single-crystal X-ray diffraction studies. The dinuclear hydride complex 3b exhibits a quadruply bridged {Zr2(μ-H)4} core in solution and in the solid state with a relatively short Zr...Zr distance of 2.8752(11) . Density functional theory computations at the B3PW91 level reproduced this structure (Zr...Zr distance of 2.900 ). The cationic hydride complex 3b reacted with excess carbon monoxide in tetrahydrofuran at room temperature to give ethylene in 25% yield based on 3b. Upon analysis of 13C NMR spectra of the reaction mixture using 13CO, oxymethylene and enolate complexes were detected as intermediates among other complexes.