Guanghui Zhu

Engineering Porous Organic Cage Crystals with Increased Acid Gas Resistance.

Both known and new CC3-based porous organic cages are prepared and exposed to acidic SO2 in vapor and liquid conditions. Distinct differences in the stability of the CC3 cages exist depending on the chirality of the diamine linkers used. The acid catalyzed CC3 degradation mechanism is probed via in situ IR and a degradation pathway is proposed and supported with computational results. CC3 crystals synthesized with racemic mixtures of diaminocyclohexane exhibited enhanced stability compared to CC3-R and CC3-S. Confocal fluorescent microscope images reveal that the stability difference in CC3 species originates from an abundance of mesoporous grain boundaries in CC3-R and CC3-S, allowing facile access of aqueous SO2 throughout the crystal, promoting decomposition. These grain boundaries are absent from CC3 crystals made with racemic linkers.

Three-step cascade over a single catalyst: synthesis of 5-(ethoxymethyl)furfural from glucose over a hierarchical lamellar multi-functional zeolite catalyst

The synthesis of hierarchical lamellar zeolites with a controlled meso-/microporous morphology and acidity is an expanding area of research interest for a wide range of applications. Here, we report a one-step synthesis of a hierarchical meso-/microporous lamellar MFI–Sn/Al zeolite (i.e., containing both Lewis acidic Sn- and Al-sites and a Bronsted acidic Al–O(H)–Si site) and its catalytic application for the conversion of glucose into 5-(ethoxymethyl)furfural (EMF). The MFI–Sn/Al zeolite was prepared with the assistance of a diquaternary ammonium ([C22H45–N+(CH3)2–C6H12–N+(CH3)2–C6H13]Br2−, C22-6-6) template in a composition of 100SiO2/5C22-6-6/18.5Na2O/xAl2O3/ySnO2/2957H2O (x = 0.5, 1, and 2; y = 1 and 2, respectively). The MFI–Sn/Al zeolites innovatively feature dual meso-/microporosity and dual Lewis and Bronsted acidity, which enabled a three-step reaction cascade for EMF synthesis from glucose in ethanol solvent. The reaction proceeded via the isomerization of glucose to fructose over Lewis acidic Sn sites and the dehydration of fructose to 5-hydroxymethylfurfural (HMF) and then the etherification of HMF and ethanol to EMF over the Bronsted acidic Al–O(H)–Si sites. The co-existence of multiple acidities in a single zeolite catalyst enabled one-pot cascade reactions for carbohydrate upgrading. The dual meso-/microporosity in the MFI–Sn/Al zeolites facilitated mass transport in processing of bulky biomass molecules. The balance of both types of acidity and meso-/microporosity realized an EMF yield as high as 44% from the glucose reactant.