Stabilizing Low‐Silica Zeolites through Aluminum Sulfate Assisted Cannibalistic Dealumination

Abstract

Av ersatile dealumination strategy was proposed to stabilize low-silica zeolitest hrough cannibalistic interaction between the host framework Al (FAL) and the guest aluminum salt. It is possible to capture selectively the FALa nd Na ions in NaY zeolite by employing as pecial externalA ls ource such as aluminum sulfate as the dealuminating agent.T his unique postmodification reduces the FALa mount efficiently and converts the chemically reacted Al species into a g-alumina support for the catalytically active component of zeolite,w hich avoidsw asting Al sources. Possessing greatly enhanced hydrothermal stability, newly generated intracrystal mesopores,a sw ella sa no ptimized distribution of FAL, the resultantd ealuminatedYzeolite catalysts can be used practically in heavy oil cracking.Zeolite catalysts are widely utilized in the petrochemical and oil-refining industries of today and are expected to live vividly into the future,a st here is increasing interest in new applications to biomass and the pyrolysis oils industry. [1] Zeolites often suffer from the fatal shortcomings of easy coking and deactivation, especially at high operation temperatures, and thus, the catalytic activity must be recovered by burning off the coke formed at temperatures up to 800 8C. [2] In this sense, zeolites with high framework Si/Al ratios (FSARs) are more favorable owing to improvedt hermal and hydrothermal stabilities. [3] Amongv ariousl ow-silica zeolites, Yzeolite with the FAUt opology has been proven to be the most useful and important catalyst for fluid catalytic cracking (FCC) and hydrocracking, which have contributed greatly to the petrochemical industry and the energy societyi nt he past 60 years. Nevertheless, pre-dealumination is definitely needed, as Yzeolite is obtained only at aF SAR below 3i nd irecth ydrothermal synthesis. [4] Post-dealuminationi ncreases the Si/Al ratio of the zeolite framework, which in turn brings about new benefits, for example, optimized distribution of framework Al (FAL), improved acid strength,a nd an optionally generated secondary mesopore system. [3,5] In the past decades, extensive studies from the academic and industrial communities have established three chemical or physicochemical wayst hat can be used for the dealumination of Yzeolite:F AL extraction with complexing agents, steamingassisted hydrothermald ealumination, and isomorphous substitution of Si for FALw ith external SiCl 4 or (NH 4 ) 2 SiF 6 . [4] Complexing agentss uch as ethylenediaminetetraacetic acid and (NH 4 ) 2 SiF 6 are toxic and costly,w hereass olid-gas modification with SiCl 4 vapor needs harsh operating conditions. Thus, hydrothermal dealumination is currently the most used in industry.H owever,t his method requires extremelyh igh operating temperatures, and it is only applicable to NH 4 NaY or HNaY zeolite but not NaY. [6] Therefore, novel techniques characteristic of eco-efficient dealumination and mild operating conditions are still highly desirable for developing useful Yzeolite based FCC catalysts.Al 3 + ions pr...

Regulation of the Si/Al ratios and Al distributions of zeolites and their impact on properties

“…In solution, Al 2 (SO 4 ) 3 can react with the framework Al of zeolites containing Na + to form the mineral natroalunite (NaAl 3 (SO 4 ) 2 (OH) 6 ), resulting in the extraction of the framework Al and thus the increase of the Si/Al ratios. 136 With this method, the Si/Al ratio of the framework of NaY can be increased to 4.2 from 2.4, while that of Beta zeolite can be increased up to 12.4 from 4.6. 43,136 Besides reacting with the framework Al of zeolite, breaking the Al-O bonds can also lead to the removal of framework Al.…”

“…136 With this method, the Si/Al ratio of the framework of NaY can be increased to 4.2 from 2.4, while that of Beta zeolite can be increased up to 12.4 from 4.6. 43,136 Besides reacting with the framework Al of zeolite, breaking the Al-O bonds can also lead to the removal of the framework Al. In fact, water in steam form can break the Al-O bonds via hydrolysis (Fig.…”

Recent progress in the improvement of hydrothermal stability of zeolites

“… 33 A versatile dealumination strategy was also proposed by Shi et al to stabilize Al-rich zeolites through interaction between the zeolite framework Al and aluminum sulfate. 73 Although high silica zeolites are hydrothermally more stable than aluminum rich zeolites, which are more susceptible to dealumination, the lack of exchangeable cation sites makes the former unsuitable for numerous applications. Under such circumstances, it becomes necessary to select zeolites with an optimum Si/Al ratio to maintain a balance between activity and hydrothermal stability.…”

Further Findings on the Stabilization Mechanism among Modified Y Zeolite with Different Rare Earth Ions

“…Since the bond energy of the Si–O bond is larger than that of the Al–O bond, , based on the cognition of the dealumination mechanism, some scholars , tried to directly synthesize Y zeolite with high Si/Al ratio through the choice of template agent, but due to the limited increase of Si/Al, its hydrothermal stability is still not ideal. Therefore, from the perspective of adjusting or strengthening the T–O (T = Si, Al) bonds, a great deal of research has been done on dealumination modification (hydrothermal dealumination, , chemical dealumination , ) and dealumination with silicon supplementation , in an attempt to achieve the purpose by increasing the proportion of Si–O bonds. The previously mentioned works fulfill the goal of enhancing hydrothermal stability, but due to the large number of missing skeleton Al atoms (active sites), the retention of acidic sites was seriously affected, eventually leading to catalyst deactivation.…”