A simple amphiphilic surfactant containing a mono-quaternary ammonium head group (N -methylpiperidine) is effective in imparting substantial mesoporosity during synthesis of SSZ-13 and ZSM-5 zeolites. Highly mesoporous SSZ-13 prepared in this manner shows greatly improved catalytic performance in the methanol-to-olefins reaction compared to bulk SSZ-13.

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Lutidine-derived bis-N-heterocyclic carbene (NHC) ruthenium CNC-pincer complexes (Ru-CNC's) were prepared. Depending on the synthetic procedure, normal (1, 2) or mixed normal/abnormal NHC-complexes (3) are formed. In the presence of phosphazene base, Ru-CNC complexes activate nitriles to give ketimino compounds 4-6. Nitrile adduct 4 shows reactivity toward strong bases to yield dearomatized complex 7, which heterolytically activates H₂ to form the bis-hydrido complex 8. Finally, these Ru-CNC's are active in catalytic hydrogenation of CO₂ to formate salts, and unlike the phosphine-containing Ru-PNP counterpart, they also catalyze the selective hydrogenation of esters to alcohols.

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The use of hydrogen as a fuel requires both safe and robust technologies for its storage and transportation. Formic acid (FA) produced by the catalytic hydrogenation of CO₂ is recognized as a potential intermediate H ₂ carrier. Herein, we present the development of a formate-based H₂ storage system that employs a Ru PNP-pincer catalyst. The high stability of this system allows cyclic operation with an exceptionally fast loading and liberation of H₂. Kinetic studies highlight the crucial role of the base promoter, which controls the rate-determining step in FA dehydrogenation and defines the total H₂ capacity attainable from the hydrogenation of CO₂. The reported findings show promise for the development of practical technologies that use formic acid as a hydrogen carrier. Like pinning down an ant: An Ru PNP catalyst provides unprecedented rates of CO₂ hydrogenation up to 1 100 000 h^-1 (turnover number >200 000) and excellent activity in the dehydrogenation of formic acid in DMF if used with the non-nucleophilic 1,8-diazabicyclo[5.4.0]undec-7-ene base. Unlike amine-based systems, this medium allows us to achieve high formate capacity together with rapid H₂ charging and release.

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The reaction mechanism of CO₂hydrogenation by pyridine-based Ru-PNP catalyst in the presence of DBU base promoter was studied by means of density functional theory calculations. Three alternative reaction channels promoted by the complexes potentially present under the reaction conditions, namely the dearomatized complex 2 and the products of cooperative CO₂(3) and H₂(4) addition, were analysed. It is shown that the bis-hydrido Ru-PNP complex 4 provides the unique lowest-energy reaction path involving a direct effectively barrierless hydrogenolysis of the polarized complex 5∗. The reaction rate in this case is controlled by the CO₂activation by Ru-H that proceeds with a very low barrier of ca. 20 kJ mol^-1. The catalytic reaction can be hampered by the formation of a stable formato-complex 5. In this case, the rate is controlled by the H₂insertion into the Ru-OCHO coordination bond, for which a barrier of 65 kJ mol^-1is predicted. The DFT calculations suggest that the preference for the particular route can be controlled by varying the partial pressure of H₂in the reaction mixture. Under H₂-rich conditions, the former more facile catalytic path should be preferred. Dedicated kinetic experiments verify these theoretical predictions. The apparent activation energies measured at different H₂/CO₂molar ratios are in a perfect agreement with the calculated values. Ru-PNP is a highly active CO₂hydrogenation catalyst allowing reaching turnover frequencies in the order of 10⁶h^-1at elevated temperatures. Moreover, a minor temperature dependency of the reaction rate attainable in excess H₂points to the possibility of efficient CO₂hydrogenation at near-ambient temperatures. This journal is

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A series of faujasite zeolites was modified by extraframework Al (Al_EF) with the goal to investigate the influence of such species on the intrinsic Brønsted acidity and catalytic activity towards paraffin cracking. The chemical state of Al_EF and zeolite acidity were investigated by ²⁷Al MAS NMR and CO_ads IR spectroscopy, H/D exchange reaction, and propane cracking. Strongly acidic defect-free Y zeolites were obtained by substitution of framework Al by Si with (NH₄)₂SiF₆. In accordance with the next-nearest-neighbor model, the intrinsic acidity of the protons increased with decreasing framework Al density. This increased acidity was evidenced by an increased shift of the OH stretching vibration upon CO adsorption in CO_ads IR spectroscopy and by an increased H/D exchange rate in H/D exchange reactions with perdeuterobenzene. All of the acid sites in these zeolites were of equal strength beyond a certain Si/Al ratio. The increased acidity resulted in an enhanced propane cracking activity. Modification of a model dealuminated Y zeolite by Al_EF only resulted in a small fraction of cationic Al_EF species, because it was difficult to control the ion exchange process. In comparison, commercial ultrastabilized Y zeolites contained less Al_EF and these species were predominantly present in cationic form. The rate of propane cracking strongly correlated to the concentration of Brønsted acid sites perturbed by cationic Al_EF species. The results of MQMAS ²⁷Al NMR spectroscopy confirmed the presence of sites perturbed by Al_EF and unaffected framework Al sites. Zeolites with higher intrinsic cracking activities contained a higher proportion of perturbed sites. Although CO_ads IR and H/D exchange methods proved to be suitable methods to probe the acidity of Y zeolites free from Al_EF, they were less suitable to predict the reactivity if the Brønsted acid sites were affected by cationic Al_EF species.

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Interaction of hydrogen with model Cu-Zn methanol synthesis catalyst prepared by decomposition of mixed hydroxicarbonate is studied by inelastic neutron scattering, in situ FTIR/MS, and thermal analysis. Reduced (Cu _0.08,Zn_0.92)O mixed oxide accumulates 6H/Cu, mainly as hydride, hydroxyl and formate species. The reduction of copper in the (Cu,Zn)O mixed oxide occurs via a reversible redox interaction with H₂ and absorption of protons as OH^--groups with ν = 3250 cm^-1 and δ ≈ 1430-1480 cm^-1. Kinetic and thermodynamic parameters of this process are evaluated. The weight loss during the reduction is due to the decomposition of the residual carbonate groups to CO₂ via formate intermediates, which occurs in the presence of hydrogen. Exposure of (Cu,Zn)O to air prior to the reduction strongly affects the kinetic parameters of the reduction process.

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The metal-ligand cooperative activation of CO₂ with pyridine-based ruthenium PNP pincer catalysts leads to pronounced inhibition of the activity in the catalytic CO₂ hydrogenation to formic acid. The addition of water restores catalytic performance by activating alternative reaction pathways and leads to unprecedented Ru-catalyzed CO₂ hydrogenation activity. The mechanism of the underlying chemical transformations is proposed on the basis of DFT calculations, kinetic experiments, and NMR reactivity studies.

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Two-line ferrihydrite (2L-FH) is a metastable, heavily disordered, partially hydrated Fe(III) oxide. The catalyst prepared by heat treatment of 2L-FH promoted with chromium ions (̃9 at %) and copper ions (4-7 at %) is much more active in the water gas shift (WGS) reaction at low temperatures (<350°C) than the conventional Fe-containing catalysts. According to XAFS spectroscopy data, the copper cations in 2L-FH are in the Cu2+ state and are in a tetragonally distorted octahedral environment, while under the WGS conditions at <350° C, copper is in the reduced state, specifically, in the form of ultrafine (<2 nm) Cu0 particles. It is due to these particles that the catalyst is very active below 350°C. Above 400°C, the Cu0 parti-cles are deactivated under the reaction conditions and the catalytic activity is only due to iron active sites, whose number is proportional to the specific surface area of the catalyst. The specific activity of the catalyst at these temperatures is close to the activity of the conventional (hematite-based) WGS catalysts. The high activity of the 2L-FH-based catalyst at <350°C makes it possible to reduce the starting temperature of the adiabatic high-Temperature WGS reactor.@en

Cobalt and aluminum hydroxo compounds with the hydrotalcite-type structure containing nitrate, carbonate, and hydroxyl groups are formed due to the deposition by precipitation of cobalt cations from a nitrate solution on 8- and y-Al 2 O 3 under the conditions of urea hydrolysis. The influence of the method of preparation on the anionic composition of the hydroxo compounds (precursors of the Co-Al catalyst) was studied. A correlation between the anionic composition of the precursor compound and the catalytic properties of the catalysts in the Fischer-Tropsch synthesis was established.@en

The anionic composition, structural parameters, optical properties and reduction behavior of Cu-MgO solid solution in hydrogen dramatically change after exposure to air. The air-exposed Cu-Mg oxide contains a lot of CO 3 2- and OH- anions. Its reduction proceeds via two stages: (1) diffusion of Cu2+ to the surface and (2) chemical interaction of Cu2+ with hydrogen. The effective activation energy gradually increases from that of the chemical step (65 kJ/mol) to that of the transport step of Cu2+ diffusion (130 kJ/mol). This behavior follows the "compensation effect", which is close to those reported earlier for CuO reduction. On the contrary, reduction of Cu2+ from the Cu-Mg oxide sample, which was not exposed to air after thermal pretreatment in the inert gas, proceeds in one step at 120-160°C with the effective activation energy of 19 kJ/mol, which is manifold less than the reported effective activation energies for various Cu-oxide systems. Water molecules eliminate from the sample slowly along with further heating up to 450°C.@en

The chapter reviews the data on the 2-line ferrihydrite structure and texture, methods for its preparation, and catalytic properties of 2LFH-based catalysts. Since 2-line ferrihydrite is metastable, the necessity and possibility of inhibiting its crystallization to hematite is discussed and new data on the kinetics of crystallization process are reported, including the effect of Al3+, Cr3+, and Cu2+ promotion. During discussion, particular attention is paid to the potential of 2LFH in catalytic application.@en

The reduction of copper chromite, CuCr₂O₄, is followed by means of thermogravimetric analysis. The reduced state is studied by means of FT IR spectroscopy, Raman spectroscopy and inelastic neutron scattering. The reduction of copper occurs in two stages: absorption of hydrogen at 250-400 °C and dehydration of the reduced state at above 450 °C. The measured vibrational spectra prove that a considerable amount of hydrogen is absorbed by the oxide structure with absorbed protons stabilized in OH and HOH-groups (geminal protons). Three groups of vibration bands are observed in the INS spectra, which can be assigned to stretching, bending and libration vibrations. An increase in the reduction temperature of copper chromite results in softening of the stretching and hardening of the bending vibrations, what can be related to the strengthening of hydrogen bonding.

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