[catalytic] H- zsm-5 molecular sieve of methanol catalytic conversion of olefins: the reaction path is related to the skeleton aluminum drop

In recent years, methanol olefins (MTO), as a non-oil route for producing important chemicals from coal, natural gas and biomass, has attracted much attention in recent years.
Because the MTO reaction is a typical acid catalysis reaction, the catalytic performance of molecular sieve catalyst in this reaction is closely related to the distribution of acid center (the lag of the skeleton aluminum).
However, it is still not clear to this day that the mechanism of the role of the acid center in the MTO catalysis reaction of molecular sieve skeleton aluminum at the atomic level.

Jian-guo wang shanxi institute of coal chemistry, Chinese academy of sciences researchers group by changing the silicon source (silica sol and ethyl orthosilicate), water bounding into two series of H - ZSM - 5 molecular sieve (S - HZ - m and T - HZ - m).
Results show that the two series of H - ZSM - 5 zeolite structure, morphology, and the total acid amount and acid strength similar to that of aluminum but Co (II) ultraviolet and nuclear magnetic test results showed the two on the aluminum frame setting or the distribution of acid has great difference.
In the s-hz-m series samples obtained by silica sol, the skeleton aluminum distribution in the straight channel and sinusoidal channel is relatively large.
In the sample of t-hz-m series prepared by ethyl silicate, the skeleton aluminum distribution in the intersection of the channel is relatively large.

The study found that the MTO catalytic reaction path and the hydrocarbon product selectivity of the h-zsm-5 molecular sieve were correlated with the skeleton aluminum drop (acid distribution).

At the same temperature, gas velocity and the pulse response of methanol conversion conditions, T - HZ - m series samples of MTO reaction has higher selectivity of ethylene and aromatic hydrocarbon and S - HZ - m series samples on MTO reaction has higher propylene and high olefin selectivity.
The study also found that compared with the s-hz-m series, the t-hz-m series has a higher HTI index (hydrogen transfer index), ethylene/(2-methyl butane + 2-methyl-2-butylene) ratio.
In the experiment of 13C/ 12c-methanol switching, the aromatic hydrocarbon of the t-hz-m series of samples has a higher incorporation activity of 12C, while the C4 and above of the s-hz-m series have higher 12C incorporation activity.
This indicates that the main reason for the selectivity difference of MTO products in the two series h-zsm-5 molecular sieves is the difference between the two cyclic reaction paths in s-hz-m and t-hz-m.
The MTO response in the s-hz-m series of samples is mainly olefin cycle, while the MTO reaction in the t-hz-m series of samples mainly focuses on aromatics cycle.

These results indicate that the distribution in the H - ZSM - 5 zeolite in the straight hole, sine channel Bronsted acid suitable olefins reaction path, is conducive to higher olefins, such as propylene and distribution in the channel's intersections Bronsted acid on a path to aromatic cyclic reaction, promoting the production of ethylene and aromatic hydrocarbons;
The regulation of acid distribution can change the MTO reaction path, thus significantly improving the catalytic performance of molecular sieve.

The research of molecular sieve acid sites from atomic scale effective regulation, acid bit distribution regulation is an effective dual cycle reaction path, and then improve the method of molecular sieve catalytic performance;
The research work provides a new way to understand the pore structure and acid characteristics of molecular sieve and to explore new efficient MTO catalyst and reaction process.