Methanol to olefins conversion: state of the art and prospects of development

The production of olefins by catalytic transformation of methanol on zeolites and zeotypes is of great interest to scientists and specialists in various fringe areas of national economy. Due to implementation of this process on industrial level, the attention gradually shifts from scientific studies devoted to the synthesis and modification of zeolites and zeotypes with different structure to investigation of pilot and industrial plants and determination of the main economic and environmental characteristics of both the existing and the future plants. In 2019, the development of 26 production sites in China with the annual output of 14 million tons of ethylene and propylene was licensed and 14 plants with the total capacity of 7.67 million tons of ethylene and propylene were launched. The created plants provide a complete cycle of coal processing, which consists of coal gasification units yielding syngas, units for the synthesis of methanol and olefins, their refinement and production of polyethylene and polypropylene. The total output of ethylene and propylene at the launched plants was more than 21 million tons. The paper presents a review of publications on the development and modification of catalysts as well as the technological, economic and environmental aspects of olefins production from methanol, which appeared in foreign journals in the recent five years.

Conversion of bioethanol over oxide catalysts

The conversion of bioethanol over supported oxide catalysts (CuO, ZnO, Cr2O3,CeO2) was studied, among which the most active in the production of hydrogenis 3% CuO / γ-Al2O3. Modification of 3% CuO / γ-Al2O3 catalyst with Cr2O3, ZnOand CeO2 promotes the growth of hydrogen yield. The highest concentrationof hydrogen at 300° C and a space velocity of 1 h-1 on CuO-ZnO / γ-Al2O3 was48% by volume. The acidity of catalysts for adsorption-desorption of pyridine byinfrared spectroscopy (ITI Matson FTIR) was determined. When the content ofCuO in the catalyst is increased from 1 to 3%, the amount of Lewis acidic centers(LAS) increases from 58 to 82 µmol/ gcat. Modification with chromium oxide ofthe copper catalyst increases the number of LAS from 82 to 156 µmol/ gcat byadsorption of pyridine at 150° C and from 79 to 120 µmol/ gcat with pyridineadsorption at 250° C. It has been established that an increase in the number ofLewis acid sites has a positive effect on the yield of hydrogen in the conversion ofbioethanol. According to electron microscopy, the modification of catalysts leadsto an increase in the dispersity of the catalyst and to a uniform distribution ofparticles on the surface of the catalyst, which also contributes to its greater activityin the production of hydrogen.

Cold plasmas in the modification of catalysts

Heterogeneous catalysts play an important role in the chemical industry and are also of critical importance in the general well-being of society in the 21st century. Increasing demands are being placed on catalyst performance in a number of areas such as activity, selectivity, longevity, and cost. Conventional approaches to improving catalytic performance are becoming exhausted, and novel ways of generating the increased performance are being sought. The utilization of cold plasmas has opened great opportunities for modification of catalysts, thanks to their room-temperature operations with reduced energy combustion, shortened duration, and undestroyed bulk structure. In this review, we present an assessment of the modification of catalysts by cold plasmas, with emphasis on particle sizes, dispersion of nanoparticles, distribution of elements, electronic properties, acid-base properties, surface functional groups, and metal-support interaction. Moreover, challenges and perspectives are also presented for the further modification of catalysts by cold plasmas and broadening their practical applications.

Photocatalytic fixation of nitrogen to ammonia: state-of-the-art advancements and future prospects

The state-of-the-art developments in the photocatalytic reduction of N2 to NH3 are presented by classifying the photocatalysts based on chemical composition. Additionally, the correlation between the modification of catalysts and their photocatalytic activity is highlighted.

Characteristic Modification of Catalysts by Use of a Chloride Source

Structural control and morphological modification of a series of Si-based nanostructures were studied from the viewpoint of modifying the catalyst’s characteristics. The catalyst was modified from a liquid to a solid during its growth. The growth evolution of the faceted Si nanowires occurred via a vapor–liquid–solid mechanism followed by a silicide vapor–solid–solid mechanism. The shapes of the catalysts defined the shapes of the nanowires during the vapor–solid–solid growth. The catalyst was further modified by the deposition of MnCl2. Only irregularly shaped Si particles or MnCl2 particles were observed on top of the Si nanowires. The characteristic modification of catalysts by liquid-phase crystal nucleation and deposition of liquid-phase droplets was discussed. In addition, the synthesis of a CrSi2 nanowire bundle by the formation of dense nanoparticles was studied.