Nanoporous Solid Acid Materials for Biomass Conversion into Value-Added Chemicals: Synthesis, Catalysis, and Chemistry

Growing environmental concerns associated with diminishing reserves of fossil fuels has led to accelerated research efforts towards the discovery of new catalytic processes for converting renewable lignocellulosic biomass into value-added chemicals. For this conversion, nanoporous solid acid materials have been widely used because of their excellent hydrothermal stability and molecular sieving capability. In the thesis, hierarchical Lewis acid zeolites with ordered mesoporosity and MFI topology (three dimensionally ordered mesoporous imprinted (3DOm-i) Sn-MFI) were successfully synthesized within the confined space of three dimensionally ordered mesoporous (3DOm) carbon by a seeded growth method. The obtained 3DOm-i Sn-MFI showed at least 3 times higher catalytic activities for the biomass-derived sugar isomerization than conventional Sn-MFI zeolites. This is because the mesopores in the hierarchical zeolites greatly enhance molecular transport. In addition, Lewis acid Sn-MFI combined with Pt metal nanoparticles (Pt/Sn-MFI) could oxidize glycerol to produce lactic acid (LA) under base-free conditions. Glycerol is a by-product in biodiesel synthesis. 80.5% selectivity of LA was achieved at 89.8% conversion of glycerol using a bifunctional Pt/Sn-MFI catalyst under base-free conditions. In the tandem reaction pathway, selective oxidation of glycerol to glyceraldehyde (GLA) and dihydroxyacetone (DHA) by using Pt catalysts was cascaded with Lewis acid catalyzed isomerization of GLA/DHA into LA. Moreover, morphology-tunable Lewis acid Sn-BEA with hydrophobicity was successfully synthesized by recrystallization of post-synthesized Sn-BEA (Sn-BEA-PS) using ammonium fluoride (NH4F) and tetraethylammonium bromide (TEABr). This recrystallization includes simultaneous procedures of dissolution-reassembly: i) the dissolution of Si-O bonds around silanol nests by fluoride ions, and ii) the reassembly of fragmented silica species into defect-free zeolite framework in the presence of TEA ions. The recrystallization also increased open Lewis acid Sn sites. These findings can explain why a 2.5 times higher rate of aqueous glucose isomerization was achieved on recrystallized Sn-BEA (Sn-BEA-RC), compared with Sn-BEA-PS. Moreover, in the isomerization of bulky lactose (C12 sugar) dissolved in MeOH, hierarchical Sn-BEA-RC showed a 3.2-fold higher activity than hydrothermally synthesized Sn-BEA (Sn-BEA-HF), due to the mesopores and enhanced organophobic character of the recrystallized catalyst. In the final part, renewable p-xylene synthesis was investigated. p-Xylene is a major commodity chemical used for the production of polyethylene terephthalate (PET) with applications in polyester fibers, films and bottles. Diels-Alder cycloaddition of 2,5-dimethylfuran (DMF) and ethylene with subsequent dehydration of the cycloadduct intermediate to produce p-xylene is an attractive reaction pathway for its production from biomass feedstocks. It was shown that phosphorous-containing zeolite BEA (P-BEA) is active, stable and selective for this reaction with an unprecedented p-xylene yield of 97%. It can selectively catalyze the dehydration reaction from the furan-ethylene cycloadduct to p-xylene, without performing side reactions which include alkylation and oligomerization. This acid catalyst establishes a commercially attractive process for renewable p-xylene production

Intraparticle Diffusional Effects vs. Site Effects on Reaction Pathways in Liquid-Phase Cross Aldol Reactions

Chemo- and regioselectivity in a heterogeneously catalyzed cross aldol reaction were directed by tuning the nature of the sites, textural properties and reaction conditions. Catalysts included sulfonic-acid functionalized resins or SBA-15 with varying particle size or pore diameter, H-BEA zeolites, and Sn-BEA zeotype; conditions were 25 °C to 170 °C in organic media. Benzaldehyde and 2-butanone yielded branched (reaction at -CH2- of butanone) and linear (reaction at -CH3) addition and condensation products; and fission of the branched aldol led to β-methyl styrene and acetic acid. Strong acids promoted the dehydration step, and regioselectivity originated from preferred formation of the branched aldol. Both, resins and functionalized SBA-15 materials yielded predominantly the branched condensation product, unless particle morphology or temperature moved the reaction into the diffusion-limited regime, in which case more fission products were formed, corresponding to Wheeler Type II selectivity. For Hform zeolites, fission of the branched aldol competed with dehydration of the linear aldol, possibly because weaker acidity or steric restrictions prevented dehydration of the branched aldol

Infantile Myofibromatosis:A Case with Skull and Rib Involvement

A case of infantile myofibromatosis with skull and rib involvement was reported. The patient was an 8-month old female infant presented with an enlarging skull mass. On systemic evaluation, 2 skull masses and three rib lesions were detected. Diagnosis was made histopathologically with excised skull mass. The clinicopathological features of the case are described

Prevalence, Correlates, and Comorbidity of 12-Month Tobacco Dependence among Ever-smokers in South Korea, During 1984-2001

The rate of dependence among ever-users of a drug indicates the risk of developing dependence once an individual has been exposed to the drug. This is the first study to investigate 12-month tobacco dependence (TD) among ever-smokers in a community-based population. Analyses were based on two national studies of representative samples aged 18-64 in 1984 (n=5,025) and in 2001 (n=6,275), conducted with household visits and face-to-face interviews. The rates of 12-month TD among ever-smokers in men showed no significant difference between 51.6% in 1984 and 50.6% in 2001. On the contrary, the rates in women significantly increased from 33.3% in 1984 to 52.8% in 2001. After adjusting for the sociodemographic variables, 'male gender' was significantly associated with 12-month TD among ever-smokers in 1984, but not in 2001. 'Unmarried' was significantly associated in 2001 but not in 1984. 'Alcohol dependence' was the only psychiatric disorder associated with 12-month TD in both study years. In conclusion, 12-month TD was found in about 50% of ever-smokers, and gender differences between the rates of 12-month TD which was observed in 1984 disappeared in 2001. Individuals with 12-month TD showed higher comorbidity with alcohol dependence than ever-smokers without TD

Consecutive junction-induced efficient charge separation mechanisms for high-performance MoS2/quantum dot phototransistors

Phototransistors that are based on a hybrid vertical heterojunction structure of two-dimensional (2D)/quantum dots (QDs) have recently attracted attention as a promising device architecture for enhancing the quantum efficiency of photodetectors. However, to optimize the device structure to allow for more efficient charge separation and transfer to the electrodes, a better understanding of the photophysical mechanisms that take place in these architectures is required. Here, we employ a novel concept involving the modulation of the built-in potential within the QD layers for creating a new hybrid MoS2/PbS QDs phototransistor with consecutive type II junctions. The effects of the built-in potential across the depletion region near the type II junction interface in the QD layers are found to improve the photoresponse as well as decrease the response times to 950 μs, which is the faster response time (by orders of magnitude) than that recorded for previously reported 2D/QD phototransistors. Also, by implementing an electric-field modulation of the MoS2 channel, our experimental results reveal that the detectivity can be as large as 1 × 1011 jones. This work demonstrates an important pathway toward designing hybrid phototransistors and mixed-dimensional van der Waals heterostructures

Sphingosine 1-phosphate receptor 4 promotes nonalcoholic steatohepatitis by activating NLRP3 inflammasome

BACKGROUND & AIMS: Sphingosine 1-phosphate receptors (S1PRs) are a group of G-protein-coupled receptors that confer a broad range of functional effects in chronic inflammatory and metabolic diseases. S1PRs also may mediate the development of nonalcoholic steatohepatitis (NASH), but the specific subtypes involved and the mechanism of action are unclear. METHODS: We investigated which type of S1PR isoforms is activated in various murine models of NASH. The mechanism of action of S1PR4 was examined in hepatic macrophages isolated from high-fat, high-cholesterol diet (HFHCD)-fed mice. We developed a selective S1PR4 functional antagonist by screening the fingolimod (2-amino-2-[2-(4- n-octylphenyl)ethyl]-1,3-propanediol hydrochloride)-like sphingolipid-focused library. RESULTS: The livers of various mouse models of NASH as well as hepatic macrophages showed high expression of S1pr4. Moreover, in a cohort of NASH patients, expression of S1PR4 was 6-fold higher than those of healthy controls. S1pr4(++/-) mice were protected from HFHCD-induced NASH and hepatic fibrosis without changes in steatosis. S1pr4 depletion in hepatic macrophages inhibited lipopolysaccharide-mediated Ca++ release and deactivated the Nod-like receptor pyrin domaincontainning protein 3 (NLRP3) inflammasome. S1P increased the expression of S1pr4 in hepatic macrophages and activated NLRP3 inflammasome through inositol trisphosphate/inositol trisphosphate-receptor-dependent [Ca++] signaling. To further clarify the biological function of S1PR4, we developed SLB736, a novel selective functional antagonist of SIPR4. Similar to S1pr4(+/-) mice, administration of SLB736 to HFHCD-fed mice prevented the development of NASH and hepatic fibrosis, but not steatosis, by deactivating the NLRP3 inflammasome. CONCLUSIONS: S1PR4 may be a new therapeutic target for NASH that mediates the activation of NLRP3 inflammasome in hepatic macrophages

Fabrication of hierarchical Lewis acid Sn-BEA with tunable hydrophobicity for cellulosic sugar isomerization

Lewis acid Sn-BEA catalysts with tunable morphology and hydrophobicity were successfully synthesized by the recrystallization of post-synthetic Sn-BEA in the presence of ammonium fluoride (NH4F) and tetraethylammonium bromide (TEABr). Three-dimensionally ordered mesoporous imprinted (3DOm-i) and nanocrystalline Sn-BEA catalysts with hydrophobic surface were synthesized for the first time by the method. This recrystallization method includes the dissolution of crystalline zeolite BEA by fluoride ions and the rearrangement of different types of silanol defects in the presence of TEABr. The method allows the final products to simultaneously inherit the morphology of their parent Al-BEA zeolites, and significantly reduce silanol defects within the catalysts. The Sn-BEA catalysts synthesized from the recrystallization method show largely enhanced catalytic performance for both glucose isomerization and bulky lactose isomerization in different solvents, which is presumably due to the hydrophobic surface and improved molecular transport property in the hierarchical zeolites. The recrystallization approach is a facile and reliable strategy to improve the hydrophobicity of zeolite catalysts with tunable morphologies ranging from nanocrystals to hierarchical structures.Chemical Engineerin