The Chinese Academy of Sciences uses high-performance dual-function catalysts to develop a new route for synthesis gas to aromatics

On March 31, the Shanghai Institutes for Advanced Study of the Chinese Academy of Sciences reported that researcher Gao Peng of the academy has made important breakthroughs in the research on efficient production of aromatic hydrocarbons under synthetic temperature and conditions
.
The research team developed a high-performance bifunctional catalyst with potential for industrial application, and proposed a new reaction pathway for the hydrogenation of syngas to aromatics
.

The research team constructed a scale-like encapsulated nano-hollow ZSM-5 molecular sieve and a bifunctional catalyst CMA/ZSM-5 coupled with cobalt-manganese-aluminum (CMA) oxide, and proposed a new reaction route for the hydrogenation of syngas to aromatics
.
Hydrogenation of carbon monoxide on the surface of prismatic cobalt carbide can generate C₂～C₄ olefins, C5+ olefins and C₂+ oxygenates
.
C₂～C₄ olefins enter the molecular sieve pores by diffusion, and undergo oligomerization to generate long-chain olefins, which are then cyclized and aromatized to generate aromatic hydrocarbons
.
In addition to the direct aromatization reaction of C5+ olefins, they can also react with carbon monoxide on ZSM-5 to generate 2,4-dimethylbenzaldehyde; carbon monoxide and C₂+ oxygenated compounds can also pass through the aldol ring on ZSM-5 The reaction is converted to p-tolualdehyde
.

These oxygenates are dehydrated and hydrogenated on molecular sieves to generate aromatic hydrocarbons, among which para-tolualdehyde plays a crucial role in the synthesis of para-xylene by hydrogenation of carbon monoxide
.

In this study, the bifunctional catalyst exhibits high carbon monoxide conversion, high aromatic selectivity, and high stability under mild reaction conditions, and achieves unprecedented space-time yields of para-xylene
.
By epitaxially growing a scale-like molecular sieve with the same topology on the surface of the nano-hollow ZSM-5, the team effectively passivated the acidity of the outer surface without affecting the mass transfer, and promoted the selective generation of p-xylene
.

The experimental results show that under the reaction conditions of 280 ℃ and catalyst dosage of 1000 ml/g per hour, the conversion rate of carbon monoxide reaches 70.
7%, the selectivity of aromatics in hydrocarbon products is greater than 63.
5%, and the proportion of paraxylene in aromatics is as high as 34.
7%.
The comprehensive performance is better than that of the previously reported catalytic systems
.
In addition, the activity and selectivity of the catalyst can be maintained for more than 700 hours without decay, showing excellent potential for industrial application
.

The conversion of non-petroleum-based carbon resources through synthesis gas to produce bulk chemicals can alleviate the increasingly serious oil shortage in China
.
Aromatic hydrocarbons are one of the most important bulk chemicals, especially p-xylene, and its downstream products are used in important fields such as aerospace and defense technology
.
Based on coupled catalysts, there are two reaction paths for synthesis gas to aromatics: one is to couple methanol synthesis catalyst and molecular sieve to prepare aromatics through methanol intermediate; the other is to couple Fe-based Fischer-Tropsch synthesis to olefin catalyst and molecular sieve to prepare aromatics through olefin intermediate
.
The reaction conditions of the above two types of coupled catalytic systems are relatively harsh (320 °C to 430 °C), and the catalyst activity, selectivity and stability are difficult to match
.