Experimental and DFT Study of the Partial Oxidation of Benzene by N2O over H-ZSM-5: Acid Catalyzed Mechanism

A Mechanistic Study of HZSM-5-Catalyzed Guaiacol Amination Using Photoionization Time-of-Flight Mass Spectrometry

Thermal-catalytic conversion and amination (TCC-A) of lignin and lignin derivates over zeolites is a promising and renewable method to produce aromatic amines, but suffers from product diversity. Currently, no unambiguous mechanism could fully describe the chemistry of this process. In this work, the TCC-A mechanism of guaiacol, a typical lignin model compound, with ammonia over HZSM-5 was investigated by online photoionization time-of-flight mass spectrometry combined with density functional theory. Various products including amines, pyrroles, and pyridines were identified. The formation of methylamine and aminophenol below 400 °C via nucleophilic substitutions is attributed to the strong adsorption of ammonia on the active site of HZSM-5. Aniline is the major product above 400 °C coproduced with pyrroles and pyridines. It is suggested that the reactions among radical intermediates (^•CH₃ and ^•NH₂) and molecules (guaiacol and catechol) lead to poor aniline selectivity via transmethylation, amination, and partial deoxygenation reactions. Hydroamination is proposed as the main formation mechanism of pyrroles and pyridines. The maximum yield of aniline can be achieved at 650 °C owing to the enhancement of amination and deoxygenation and the suppression of transmethylation reactions.

An efficient approach to explore the adsorption of benzene and phenol on nanostructured catalysts: a DFT analysis

The adsorption behavior of benzene and phenol on the zeolite is attributed to the differences in the strength of their interactions.

The effect of nano confinement on the C-h activation and its corresponding structure-activity relationship

The C–H activation of methane, ethane, and t-butane on inner and outer surfaces of nitrogen-doped carbon nanotube (NCNTs) are investigated using density functional theory. It includes NCNTs with different diameters, different N and O concentrations, and different types (armchair and zigzag). A universal structure-reactivity relationship is proposed to characterize the C–H activation occurring both on the inner and outer surfaces of the nano channel. The C–O bond distance, spin density and charge carried by active oxygen are found to be highly related to the C–H activation barriers. Based on these theoretical results, some useful strategies are suggested to guide the rational design of more effective catalysts by nano channel confinement.

EFFECT OF HIGH-LEVEL LAYER SELECTION IN ONIOM ON Na+ ADSORPTION IN ZSM-5 ZEOLITE

Here we present a systematical investigation on the effect of high-level layer selection in our own N-layered integrated molecular orbital + molecular mechanics (ONIOM) method. We used the adsorption of Na+ in the M7 site of ZSM-5 as an instructive example. We embedded n tetrahedral sites (nT= 7, 19, 22, 33) for high-level layer into a low-level layer represented by 75T (denoted as nT@75T). Our calculations showed that 7T@75T behaved poorly in both structure optimization and interaction energy calculation. Hence only including the first coordination circle of the ion (i.e. 7T), as commonly used in literature, is not sufficiently good. However, for n ≥ 19, both structure optimization and interaction energy calculation by ONIOM are in good agreement with the full 75T model calculation. Such a reliable ONIOM calculation needs only 1/10 to 1/5 computational time for each self-consistent field (SCF) iteration as compared to the full 75T model calculation, highlighting its pivotal role in zeolite simulation.

Alkane activation over acidic zeolites: the first step

The heterogeneous acid-catalyzed activation step of alkanes leading to the reaction intermediates (carbocationic or alkoxy species) was up to now the matter of a longstanding controversy. Gas chromatography and online mass spectroscopy measurements show that H(2) and methane are formed over H-zeolites, whereas HD and CH(3)D are formed over D-zeolites as the primary products in the reaction with isobutane. These results indicate that sigma-bond protolysis by strong acid sites is the first step for hydrocarbon activation on these catalysts at mild temperatures (473 K), in analogy to the activation path occurring in liquid superacid media.

Weakly Bound Complexes of N2O: An ab Initio Theoretical Analysis Toward the Design of N2O Receptors

Ab initio calculations at MP2/6-311++G(2d,2p) and MP2/6-311++G(3df,3pd) computational levels have been used to analyze the interactions between nitrous oxide and a series of small and large molecules that act simultaneously as hydrogen bond donors and electron donors. The basis set superposition error (BSSE) and zero point energy (ZPE) corrected binding energies of small N2O complexes (H2O, NH3, HOOH, HOO*, HONH2, HCO2H, H2CO, HCONH2, H2CNH, HC(NH)NH2, SH2, H2CS, HCSOH, HCSNH2) vary between -0.93 and -2.90 kcal/mol at MP2/6-311++G(3df,3pd) level, and for eight large complexes of N2O they vary between -2.98 and -3.37 kcal/mol at the MP2/6-311++G(2d,2p) level. The most strongly bound among small N2O complexes (HCSNH2-N2O) contains a NH..N bond, along with S-->N interactions, and the most unstable (H2S-N2O) contains just S-->N interactions. The electron density properties have been analyzed within the atoms in molecules (AIM) methodology. Results of the present study open a window into the nature of the interactions between N2O with other molecular moieties and open the possibility to design N2O abiotic receptors.