Stability of Zeolites in Aqueous Phase Reactions

Prodinger, Sebastian; Shi, Hui; Eckstein, Sebastian; Hu, Jian Zhi; Olarte, Mariefel V.; Camaioni, Donald M.; Derewinski, Miroslaw A.; Lercher, Johannes A.

doi:10.1021/acs.chemmater.7b01847

Cited by 60 publications

(57 citation statements)

References 48 publications

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“…The successful synthesis of RuO 2 @MOF-808-P results in modulated CO/O adsorption behavior and a remarkable improvement in the CO oxidation performance on the RuO 2 surface at low temperatures. The PEGS method can be extended to other guests and nanoporous hosts with reasonable stability under desired synthesis conditions (Supplementary Figure 25 ) 24 , 64 . In theory, the PEGS approach is applicable to metals, oxides, hydroxides and sulfides 65 as long as their relevant Pourbaix diagrams indicate the feasibility of their formation.…”

Section: Discussionmentioning

confidence: 99%

Rational approach to guest confinement inside MOF cavities for low-temperature catalysis

et al. 2019

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Geometric or electronic confinement of guests inside nanoporous hosts promises to deliver unusual catalytic or opto-electronic functionality from existing materials but is challenging to obtain particularly using metastable hosts, such as metal–organic frameworks (MOFs). Reagents (e.g. precursor) may be too large for impregnation and synthesis conditions may also destroy the hosts. Here we use thermodynamic Pourbaix diagrams (favorable redox and pH conditions) to describe a general method for metal-compound guest synthesis by rationally selecting reaction agents and conditions. Specifically we demonstrate a MOF-confined RuO2 catalyst (RuO2@MOF-808-P) with exceptionally high catalytic CO oxidation below 150 °C as compared to the conventionally made SiO2-supported RuO2 (RuO2/SiO2). This can be caused by weaker interactions between CO/O and the MOF-encapsulated RuO2 surface thus avoiding adsorption-induced catalytic surface passivation. We further describe applications of the Pourbaix-enabled guest synthesis (PEGS) strategy with tutorial examples for the general synthesis of arbitrary guests (e.g. metals, oxides, hydroxides, sulfides).

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Section: Discussionmentioning

confidence: 99%

Rational approach to guest confinement inside MOF cavities for low-temperature catalysis

et al. 2019

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“…At a low Si/Al ratio (e.g., 15-50 for BEA), the concentration of Brønsted acid sites becomes decisive as it influences the amount of water in pores available for hydrolysis ( Figure 5C). [84,88] In the case of multicomponent systems (e.g., water solutions), water molecules are competing with less polar molecules for adsorption in pores. Zeolites with lower concentrations of acid sites tend to adsorb a smaller quantity of water from steam and therefore are more stable in comparison with aluminum-rich ones, while for liquid water conditions the trend is the opposite (increase in Si/Al results in decreased stability).…”

Section: Hot Liquid Watermentioning

confidence: 99%

Zeolite (In)Stability under Aqueous or Steaming Conditions

et al. 2020

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zeolites, modification of zeolite acidity for use as fluid catalytic cracking (FCC) catalysts or even for the preparation of novel zeolite frameworks. [1] Considering the significance of zeolite applications at the industrial level, a thorough understanding of zeolite (in)stability under aqueous conditions has been identified as a very important problem in catalysis and zeolite science. Zeolite (in)stability in water or under steaming conditions has been investigated by a number of experimental techniques, in particular magic angle spinning (MAS) NMR, IR, powder X-ray diffraction (PXRD), calorimetry and adsorption. Experimental studies have often been augmented by computational modeling and a large number of relevant theoretical papers can be found in the literature. While the main focus of this review is on reactive interactions of water with zeolites, it is also important to review the most important observations obtained for nonreactive water adsorption in zeolites. It is not surprising that all-silica zeolites, which exhibit negligible water uptake are stable even under conditions where Alcontaining zeolites lose crystallinity: the effective framework hydrolysis can only take place when sufficient water is present in the zeolite channel system. The amount of water inside the zeolite channels depends critically on the concentration of heteroatoms and/or framework defects, such as silanol nests, which show much higher affinity toward water than hydrophobic SiOSi bridges. Zeolite hydrophobicity increases with increasing Si/Al ratio and incomplete pore filling by water is commonly observed for zeolites with high Si/Al at standard pressure. It has been suggested already in the 1950s by Young that water can only adsorb on surface silanol groups, while the parts of the silica surfaces formed by SiOSi bridges are hydrophobic. [2] Both water adsorption in zeolites and zeolite (in)stability under aqueous conditions depend on the zeolite composition (Si/Al ratio, charge-compensating cations, and defect concentration in particular). Our primary goal is to review the most critical aspects of zeolite (in)stability for a broad range of temperature and partial water pressure (p 0), focusing on the framework zeolite composition (Si/Al ratio and presence of Ge, Sn, and Ti heteroatoms) and defect concentration. Zeolites (in)stability in water is discussed for increasing extent of framework degradation, starting from the nonreactive interaction with water, reversible hydrolysis of TO bonds, mild zeolite demetallation, mesopore formation, and total amorphization (Figure 1). Zeolites are among the most environmentally friendly materials produced industrially at the Megaton scale. They find numerous commercial applications, particularly in catalysis, adsorption, and separation. Under ambient conditions aluminosilicate zeolites are stable when exposed to water or water vapor. However, at extreme conditions as high temperature, high water vapor pressure or increased acidity/basicity, their crystalline framework can be destroyed....

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“…A particular influence of the fluoride route is the significant reduction of the amount of silanol defects, resulting in more hydrophobic and hydrothermally stable materials in comparison to zeolites conventionally prepared in alkaline media. [10][11][12] More recently, it has also been reported that introduction of NaF during the synthesis of high-silica CHA zeolites results in additional (intracrystalline) microporosity, which can greatly enhance mass transport of reactants to active sites during catalysis. 13,14 Framework etching with HF or NH 4 HF 2 is another method to introduce additional porosity in zeolites.…”

Section: Introductionmentioning

confidence: 99%