Reversible Nature of Coke Formation on Mo/ZSM‐5 Methane Dehydroaromatization Catalysts

Non‐oxidative dehydroaromatization of methane over Mo/ZSM‐5 zeolite catalysts is a promising reaction for the direct conversion of abundant natural gas into liquid aromatics. Rapid coking deactivation hinders the practical implementation of this technology. Herein, we show that catalyst productivity can be improved by nearly an order of magnitude by raising the reaction pressure to 15 bar. The beneficial effect of pressure was found for different Mo/ZSM‐5 catalysts and a wide range of reaction temperatures and space velocities. High‐pressure operando X‐ray absorption spectroscopy demonstrated that the structure of the active Mo‐phase was not affected by operation at elevated pressure. Isotope labeling experiments, supported by mass‐spectrometry and ¹³C nuclear magnetic resonance spectroscopy, indicated the reversible nature of coke formation. The improved performance can be attributed to faster coke hydrogenation at increased pressure, overall resulting in a lower coke selectivity and better utilization of the zeolite micropore space.     

Activation of Mo/HZSM-5 for methane aromatization

The effect of Mo/HZSM-5 pretreatment at 973 K in inert (He), oxidizing (artificial air), and carbu-rizing (CH4/He mixture) atmospheres on its performance in non-oxidative methane dehydroaroma-tization (MDA) was investigated. The effect of post-synthesis silylation on deactivation of external acid sites was also studied. Precarburization resulted in increased aromatic selectivity and im-proved catalyst stability. The benzene selectivity was the highest for the silylated Mo/HZSM-5 cata-lyst (benzene+naphthalene selectivity after 1 h on stream was close to 100%). The deactivation of precarburized zeolites was less pronounced than that of zeolites heated in air or He. During heating in air or He, larger fractions of the molybdenum oxide species diffused into the micropores than during heating in methane. Carburization of the molybdenum oxide species in the micropores dur-ing MDA resulted in the formation of molybdenum carbide particles, and these contributed to pore blocking, making the Br?nsted acid sites inaccessible. The formation of molybdenum carbides dur-ing heating in methane resulted in a less mobile Mo phase. It is argued that the presence of molyb-denum carbide particles in the micropores contributes to rapid catalyst deactivation, in addition to the formation of hard coke on the external surface.     

Tetrabromo(2‐methylpyridine‐N)titanate(IV)

The reaction of 2‐methyl­pyridine with TiBr₄ affords tetra­bromo(2‐methyl­pyridine‐N)­titanate(IV), C₆H₇Br₄NTi. The environment around the Ti atom can be described as a slightly distorted trigonal bipyramid, with the nitro­gen base occupying an equatorial position. The crystal structure of the title compound is isomorphous with tetra­chloro(2‐methyl­pyridine‐N)­titanate(IV).     

Site regeneration in the Fischer-Tropsch synthesis reaction: a synchronized CO dissociation and C-C coupling pathway

A critical issue in the Fischer-Tropsch synthesis reaction is the blocking of the active sites for low barrier CO dissociation by the C(1) adsorbed species generated from CO dissociation, which can hinder the further steps in the FT process. Here, we propose a synchronized pathway for low barrier CO dissociation and C-C coupling on a corrugated Ru surface.     

Nonhydrothermal Synthesis and Properties of Saponite-Like Materials

Main features of nonhydrothermal synthesis of saponite-like materials containing Zn(II) and Mg(II) cations in octahedral networks were studied. Optimal conditions for the synthesis were determined. The influence exerted by the double-charged structure-forming cation on the rate of structure formation in the synthesized materials and also on their pore structure and thermal stability was studied.