Mesoporous Zirconium Oxide Prepared by Anchoring W, Mo, Nb, Ta Using Peroxo Precursors: Influence of the Oxoanions on the Pores Size and the Hydrothermal Catalysts Stability for Cellulose Conversion

Influence of Brønsted and Lewis acidity of the modified Al-MCM-41 solid acid on cellulose conversion and 5-hydroxylmethylfurfuran selectivity

In this study, which incorporates many principles of green chemistry (use of renewable feedstocks, catalysis, improvement of energy efficiency, and harmless solvents and auxiliaries), the single-phase catalytic conversion of cellulose to 5-HMF in over silica-alumina catalysts was investigated. A series of dual-template silica-alumina catalysts with CTAB as the main template and F127 or triethylamine (TEA) as the co-template were synthesized at a low temperature of 60 °C and characterized by XRD, N2 adsorption-desorption technique, FT-IR and pyridine adsorption FT-IR. The surface area is increased by using the second template in silica-alumina catalyst. In addition, the acidity of the surface was changed by using the second template. The cellulose conversion and yield of 5-HMF increased from 36% to 52% and from 3.13% to 4.24%, respectively, due to the properties gained by using the second template. 52% cellulose conversion and 8.13% selectivity of 5-HMF were obtained in aqueous medium, 220 °C and 6 h reaction time with the catalyst using TEA as co-template. Eco-friendly silica catalysts synthesized at low temperatures with a dual template can be considered as a potential alternative for the conversion of cellulose into value-added biobased products.

Three types of silica-zirconia membranes of different zirconia content were prepared by the sol-gel method to test their stability and H2 separation performance in hydrothermal conditions. Some silica-zirconia membranes were prepared by “steam-firing” in which firing was carried out in steamed air in order to increase the hydrothermal stability, and then tested in hydrothermal conditions. The activation energy of H2 and He permeation increased with increasing zirconia content, suggesting that the networks of silica-zirconia matrix were densified with increasing zirconia content. In the hydrothermal conditions, the activation energy of H2 and He permeation also increased, indicating clearly that silica-zirconia membranes were also densified by water vapor at high temperature. The pores for N2, Co2 and CH4 permeation decreased with the increasing zirconia content and vanished in the hydrothermal conditions, leaving some pinholes. Some silica-zirconia membranes were prepared by firing in steamed air in order to increase the hydrothermal stability. This method appeared to be effective to increase hydrothermal stability of the silica-zirconia membrane.

Preparation and characterization of super-microporous alumina with crystalline structure

Acidic and adsorptive properties of SBA-15 modified by aluminum incorporation

MCM-41 grafted with citric acid: The role of carboxylic groups in enhancing the synthesis of xanthenes and removal of heavy metal ions

Lactic acid is an important platform feedstock for synthesizing various chemicals. Lactic acid is normally converted from any sugar such as glucose, and Sn-β zeolite is an effective catalyst. In this study, β zeolite with different Si/Al ratios was prepared and characterized. Sn precursor is reacted with β zeolite by high-energy mixing and introduced into the framework of β zeolite to obtain Sn-β zeolite with different Si/Al ratios. The physicochemical properties of Sn-β zeolite were characterized by XRD, FTIR, N2 physical adsorption, UV Vis diffuse reflectance spectroscopy, and pyridine adsorption FTIR. The results showed that when the Si/Al molar ratio of β zeolite was less than 45, the skeleton load of Sn in β zeolite increased effectively with the decrease in aluminum content, and the Lewis acid and Brønsted acid site numbers could be improved. As the Si/Al ratio exceeded 45, the increase in Sn load in β zeolite slowed down, and the Lewis acid and Brønsted acid site numbers were decreased. The results from the catalytic conversion of glucose to lactic acid confirmed that the too high Si/Al ratio caused a decrease conversion rate. The highest performance of the prepared Sn-β zeolites with the highest catalytic efficiency had a glucose conversion rate of 96.69% and lactic acid yield of 39.42% within 7 h at 190 °C in a pressure reactor.

Development of hydrothermally stable sol–gel derived La 2O 3-doped Ga 2O 3–Al 2O 3 composite mesoporous membrane

Skeletal isomerization of 1-butene on 12-tungstophosphoric acid supported on zirconia

Production of bioadditives from glycerol esterification over zirconia supported heteropolyacids

Catalytic activity of layered α-(tin or zirconium) phosphates and chromia-pillared derivatives for isopropyl alcohol decomposition

Tin exchanged heteropoly tungstate: An efficient catalyst for benzylation of arenes with benzyl alcohol

A series of novel pyrazolyl biscoumarins was synthesized at 80 °C in a one pot procedure using an Fe3+ incorporated mesoporous silicate catalyst (FeTUD-1). The wormhole structured FeTUD-1 catalyzed the condensation of pyrazole aldehyde (1,3-diphenyl-1H-pyrazole-4-carbaldehyde) and 4-hydroxy coumarin to give the product in ∼85% yield. XRD and N2 sorption studies of FeTUD-1 confirmed its amorphous, mesoporous nature, which possessed a large surface area of 638 m2 g−1 and a pore diameter of 9.4 nm. The nature of Fe3+ ion co-ordination within the silica matrix was evaluated by different techniques including diffuse reflectance UV-Vis, FTIR, and EPR. FeTUD-1 possessed both Brønsted and Lewis acidity, as measured by FTIR of pyridine adsorption, that are responsible for the observed activities.

Regulation of Lewis acid sites on ZnO/SiW11Co for tunable photocatalytic activity toward water remediation

The microporous-mesoporous structure of nanoporous carbon and modified carbon electrodes has a strong influence on the electrochemical characteristics of the devices like supercapacitors, polymer electrolyte fuel cells and electrolysers, gas storage devices, as well as of Li-ion and Na-ion batteries. For that reason, it is crucial to have a good understanding of the porosity and hierarchical structure of carbon and modified carbon materials used [1]. As a standard method, the nitrogen adsorption measurements and various analysis theories are used. These models need the pore shape as an input parameter for detailed calculations, however, often the slit-shaped pore model is postulated without additional verification [1]. This assumption is also very often transferred to the behaviour of carbon based materials in different applications leading to some serious misinterpretations. For cost-effective hydrogen and methane based economy, efficient methods for hydrogen and methane storage are urgently needed. To improve the gas storage properties, the fundamental understanding of the confinement of the gas in microporous-mesoporous materials is inevitable. In particular, the role of confinement dimensions in the mass transfer of the hydrogen, methane as well as oxygen molecules has huge impact on the fuel cell characteristics. Our research focuses on detailed estimation of pore shape and size in various carbide-derived carbons and other carbon materials using various standardized and novel methods, like nitrogen, hydrogen and carbon dioxide adsorption measurements. All carbon samples were dried under vacuum at 350 оC at least for 24 h prior to each measurement. N2 sorption analysis at -196 оC and CO2 sorption analysis at 0 оC were carried out on an ASAP 2020 instrument (Micromeritics, USA). The experimental data were treated with classical models (BET and t-plot) as well as different NLDFT models available through 3Flex and SAIEUS (Micromeritics, USA) software [2,3]. The results for pore size distribution (PSD) calculations from N2 isotherms using a slit shape pore model and model “Carbon-N2, 2D-NLDFT Heterogeneous Surface” [4,5] (demo software SAIEUS, Micromeritics, USA) will be reported. The pore size distribution data calculated from CO2 sorption isotherms using a slit shaped pore model and model “CO2-DFT Model” (software 3Flex, Micromeritics, USA) will be discussed. Although, the pore size distributions calculated from CO2 have high level of roughness and several model artefacts (e.g. around 0.7 nm) [6,7], the results generally support the findings from N2 sorption isotherms. Raman spectra analysis, small-angle neutrons scattering and small angle X-ray scattering combined with the FIB-SEM and high resolution TEM data have been used. The results obtained are compared to the behaviour of these materials in different energy storage/conversion related devices like supercapacitors [8,9] and polymer electrolyte fuel cells 10]. As a result, the importance of hierarchical porous structure and pore shape along with pore size (pore size distribution) of used carbon materials in the energy technology applications will be addressed and demonstrated. The hydrogen sorption parameters will be compared with the methane sorption characteristics as well as correlated with PEM fuel cell and supercapacitor characteristics. Acknowledgments Authors would like to thank HZB and PSI for the allocation of neutron radiation beamtime on instruments V16 and FOCUS, respectively. The Estonian Ministry of Education and Research (institutional research project IUT20-13, personal research grant PUT55) and European Regional Development Fund (The Centres of Excellence TK117 and, TK141) for financial support.