Increasing the Number of Aluminum Atoms in T₃ Sites of a Mordenite Zeolite by Low‐Pressure SiCl₄ Treatment to Catalyze Dimethyl Ether Carbonylation

Abstract

Controlling the location of aluminum atoms in a zeolite framework is critical for understanding structure-performance relationships of catalytic reaction systems and tailoring catalyst design. Herein, we report a strategy to preferentially relocate mordenite (MOR) framework Al atoms into the desired T 3 sites by lowpressure SiCl 4 treatment (LPST). High-field 27 Al NMR was used to identify the exact location of framework Al for the MOR samples. The results indicate that 73 % of the framework Al atoms were at the T 3 sites after LPST under optimal conditions, which leads to controllably generating and intensifying active sites in MOR zeolite for the dimethyl ether (DME) carbonylation reaction with higher methyl acetate (MA) selectivity and much longer lifetime (25 times). Further research reveals that the Al relocation mechanism involves simultaneous extraction, migration, and reinsertion of Al atoms from and into the parent MOR framework. This unique method is potentially applicable to other zeolites to control Al location.

Quantitatively Mapping the Distribution of Intrinsic Acid Sites in Mordenite Zeolite by High-Field 23Na Solid-State Nuclear Magnetic Resonance

“…Four nonequivalent T-sites were clearly differentiated in the 27 Al MQ MAS NMR spectrum, and the signals in the 27 Al MAS NMR from low field to high field were uncontroversially attributed to Al atoms located in T2, T1, T4, and T3, respectively. 6 In order to provide the evidence of 23 Na signal attribution, the 23 Na- 27 Al D-HMQC MAS NMR spectrum of Na-MOR is adopted (Figure 2a), and three well distinguished correlation peaks can be observed. From the 27 Al dimension (F1), the signal at 53 ppm is attributed to Al T-sites of T1 and T2.…”

“…Correspondingly, the signals at 52 and 50.5 ppm are attributed to the Al T-sites of T4 and T3, which is consistent with our previous work. 6 Due to the spatial proximity of the Na + and Tsites of the Al atom (Figure S7), three signals from the 23 Na dimension (F2) which correspond to the three peaks of the 23 Na MQ MAS NMR spectrum are attributed to the Na VI, Na IV, and Na I sites from low field to high field. 27 Al MAS NMR and 27 Al MQ MAS NMR spectra are also acquired at 14.1 and 18.8 T (Figure S8).…”

“…In our recent work, high-field (18.8 T) 27 Al MAS NMR and 27 Al MQ MAS NMR were used conjointly to explore the MOR zeolite with higher Si/Al ratio (47.5) which was obtained by the low-pressure SiCl 4 treatment method. Four nonequivalent T-sites were clearly differentiated in the 27 Al MQ MAS NMR spectrum, and the signals in the 27 Al MAS NMR from low field to high field were uncontroversially attributed to Al atoms located in T2, T1, T4, and T3, respectively …”

“…Since 2006, mordenite (MOR) zeolite has been first reported to have excellent DME carbonylation activity . In the following decades, continuous efforts have been made on the modification of MOR zeolite to improve the activity and stability. − In January 2017, the world’s first demonstration project for the production of ethanol (>100,000 t per year) from coal by DME carbonylation, developed by the Dalian Institute of Chemical Physics of the Chinese Academy of Science, was proved completely successful in Shaanxi province of China.…”

Dynamic Evolution of Zeolite Framework and Metal-Zeolite Interface

“…Catalysts are the footstone of the modern chemical industry, which can conspicuously accelerate the reaction rate, shorten the reaction time, and reduce energy consumption. As an important type of solid catalysts, zeolites have become the backbone in some crucial chemical processes, such as fluid catalytic cracking (FCC), , methanol-to-olefin (MTO), − methanol-to-ethanol, − and coupling conversion of hydrocarbon and methanol/CO x to aromatization. − Zeolites are a class of crystalline microporous materials with a key feature of well-defined channels/cages for reactant molecules adsorption, transformation, and reaction, which are constructed from the connections of corner-sharing TO 4 tetrahedra (T = Si, Al, P, etc.). Owing to the presence of AlO 4 in aluminosilicate zeolites and SiO 4 in silicoaluminophosphate zeolites, the negative charge of zeolite framework requires a balancing cation (usually H + ) to ensure electroneutrality, resulting in another key feature of Brønsted acid sites (BAS). , By controlling the synthesis conditions, diverse metals (e.g., Ti, Sn, Ge, Zr, and Nb) can be introduced into the zeolite framework, forming heteroatomic zeolites with Lewis acidity. , Besides, the extra-framework metal species with single, cluster, and nanoparticle structures can be accommodated into zeolite channels/cages. − Until now, more than 250 topologies of zeolites with various compositions and acidities have been developed by bottom-up and top-down strategies, exhibiting many unrivalled catalytic performances (e.g., shape selectivity, − dynamic autocatalysis, , and synergistic catalysis). , Although a lot of progress has been achieved, many aspects of the active sites and catalytic mechanisms in zeolites and metal-zeolites are still under debate.…”