Improving Stability of Zeolites in Aqueous Phase via Selective Removal of Structural Defects

Abstract

Missing silicon-oxygen bonds in zeolites are shown to be the cause for structural instability of zeolites in hot liquid water. Their selective removal drastically improved their structural stability as demonstrated using zeolite beta as example. The defects in the siloxy bonds were capped by reaction with trimethylchlorosilane, and Si-O-Si bonds were eventually formed. Hydrolysis of Si-O-Si bonds of the parent materials and dissolution of silica-oxygen tetrahedra in water causing a decrease in sorption capacity by reprecipitation of dissolved silica and pore blocking was largely mitigated by the treatment. The stability of the modified molecular sieves was monitored by (29)Si-MAS NMR, transmission electron micrographs, X-ray diffraction, and adsorption isotherms. The microporosity, sorption capacity, and long-range order of the stabilized material were fully retained even after prolonged exposure to hot liquid water.

Effect of Composition of Iron-Cobalt Oxide Catalyst and Process Parameters on The Hydrothermal Liquefaction of Sugarcane Bagasse

“…These observations indicated that there was a loss of deoxygenation activity and increased polymerization activity of the catalyst which might be due to hydration and phase transformation occurred for oxides under the hydrothermal condition [40]. Developing stable catalysts under hydrothermal conditions is the key challenge for the development of economical processes for biofuel production [41] and isomorphic substitution of Fe and Co into hydrothermally stable support, such as: siliceous zeolites [42], may overcome this problem which will be the future studies.…”

Organic‐Free Synthesis of a Highly Siliceous Faujasite Zeolite with Spatially Biased Q4(nAl) Si Speciation

“…In order to validate the higher Si content of HOU-3, we performed two sets of experiments.F ollowing protocols in literature, [30] we first tested the hydrothermal stability of Na-HOU-3 against that of commercial zeolite Na-Y (Tosoh HSZ-320NAA, SAR = 2.75). As shown in Figure 5A,H SZ-320NAA loses ca.…”

Organic‐Free Synthesis of a Highly Siliceous Faujasite Zeolite with Spatially Biased Q4(nAl) Si Speciation

“…In order to validate the higher Si content of HOU‐3, we performed two sets of experiments. Following protocols in literature, we first tested the hydrothermal stability of Na‐HOU‐3 against that of commercial zeolite Na‐Y (Tosoh HSZ‐320NAA, SAR=2.75). As shown in Figure A, HSZ‐320NAA loses ca.…”