In-situ FTIR to unravel the bifunctional nature of aromatics hydrogenation synergy on zeolite / metal catalysts

Acid sites, in particular Brønsted sites, are often reported to enhance the catalytic performance of metal catalysts, like platinum, in hydrogenation. The significant boost in catalytic performance suggests a bifunctional...

Organocatalyzed Beckmann Rearrangement of Cyclohexanone Oxime by Trifluoroacetic Anhydride in a Microreactor

An efficient method for the Beckmann rearrangement of cyclohexanone oxime (CHO) catalyzed by trifluoroacetic anhydride (TFAA) is proposed in this work. The effects of experimental parameters on the reaction rate are studied, including CHO concentration, TFAA/CHO ratio, temperature, and CPL concentration. The reaction rate shows a linear relationship with TFAA/CHO ratio and reduces with the increasing of CPL concentration. Based on the experimental data and the study of in-situ FTIR, a reaction mechanism is proposed and the equilibrium relationship between CPL and TFAA is established. A rate constant model is developed and is in good agreement with the experimental results. The TFAA/TFA catalytic system allows high conversion and reaction rate compared with other organic acids.

Electrochemical oxidation of ferricyanide

We report the electrochemical oxidation of ferricyanide, [FeIII(CN)6]3− and characterised the oxidation product by in-situ FTIR and XAS spectroelectrochemistry methods. Oxidation of [FeIII(CN)6]3− is proposed to proceed via a tentative Fe(IV) intermediate that undergoes reduction elimination to give cis-[FeIII(CN)4(CH3CN)2]1− as stable product in acetonitrile. Speciation of the oxidation product by DFT calculations is underpinned by good agreement to experimental data.

Synergistic Effect of Neighboring Fe and Cu Cation Sites Boosts FenCum-BEA Activity for the Continuous Direct Oxidation of Methane to Methanol

Direct oxidation of methane to methanol (DMTM), constituting a major challenge for C1 chemistry, has aroused significant interest. The present work reports the synergistic effect of neighboring [Fe]--[Cu] cations, which can significantly boost the CH3OH productivity (100.9 and 41.9 → 259.1 μmol∙g−1cat∙h−1) and selectivity (0.28 and 17.6% → 71.7%) of the best performing Fe0.6%Cu0.68%-BEA (relative to monomeric Fe1.28%- and Cu1.28%-BEA) during the continuous H2O-mediated N2O DMTM. The combined experimental (in situ FTIR, D2O isotopic tracer technique) and theoretical (DFT, ab initio molecular dynamics (AIMD)) studies reveal deeper mechanistic insights that the synergistic effect of [Fe]--[Cu] can not only significantly favor active O production (ΔG = 0.18 eV), but also efficiently motivate the reaction following a H2O proton-transfer route (ΔG = 0.07 eV), eventually strikingly promoting CH3OH productivity/selectivity. Generally, the proposed strategy by employing the synergistic effect of bimetallic cations to modify DMTM activity would substantially favor other highly efficient catalyst designs.

The Nature of Zeolite Catalytic Sites

<p>The nature of zeolite catalytic sites was studied by observing their interactions with sorbants. In situ FTIR studies of a range of sorbants on H+ZSM-5, H+mordenite and H+Y showed that the zeolite Bronsted proton was transferred towards the sorbant. Sorbants could be placed in three classes depending on the type of hydrogen bond formed. "Class A" sorbants were alcohols, alkanes, ammonia, amines and carboxylic acids and showed a single v0-H band shifted from the vO-H of the zeolite. The shift in vO-H increased with increasing proton affinity of the sorbant. "Class B" sorbants were alkenes and aromatics and showed a resultant broad, flat vO-H due to bonding through the t electrons of the double bond or aromatic ring. "Class C" sorbants included water, ethers, ketenes, aldehydes, nitriles and carboxylic acids (also Class A). They showed extremely broad hydroxyl bands from -3700 to -1200 cm-1 with several maxima. Bonding was through oxygen or nitrogen lone electron pairs. A novel, low temperature (-400 [degrees] C), reaction of acetic acid to ketene was observed over alkali-exchanged zeolites. Thermal desorption/mass spectrometry, mini-reactor mass spectrometry and in situ FTIR techniques were used to investigate the products obtained by varying the carboxylic acid and the catalyst, and the reaction mechanism.</p>

The Nature of Zeolite Catalytic Sites

<p>The nature of zeolite catalytic sites was studied by observing their interactions with sorbants. In situ FTIR studies of a range of sorbants on H+ZSM-5, H+mordenite and H+Y showed that the zeolite Bronsted proton was transferred towards the sorbant. Sorbants could be placed in three classes depending on the type of hydrogen bond formed. "Class A" sorbants were alcohols, alkanes, ammonia, amines and carboxylic acids and showed a single v0-H band shifted from the vO-H of the zeolite. The shift in vO-H increased with increasing proton affinity of the sorbant. "Class B" sorbants were alkenes and aromatics and showed a resultant broad, flat vO-H due to bonding through the t electrons of the double bond or aromatic ring. "Class C" sorbants included water, ethers, ketenes, aldehydes, nitriles and carboxylic acids (also Class A). They showed extremely broad hydroxyl bands from -3700 to -1200 cm-1 with several maxima. Bonding was through oxygen or nitrogen lone electron pairs. A novel, low temperature (-400 [degrees] C), reaction of acetic acid to ketene was observed over alkali-exchanged zeolites. Thermal desorption/mass spectrometry, mini-reactor mass spectrometry and in situ FTIR techniques were used to investigate the products obtained by varying the carboxylic acid and the catalyst, and the reaction mechanism.</p>