Search

Ethylene glycol (EG) is obtained by a novel, two-step approach combining a biotechnological and a heterogeneously catalyzed step. First, microalgae are cultivated to photobiocatalytically yield glycolic acid (GA) by means of photosynthesis from CO

Developing functional materials from biomass is a significant research subject due to its unique structure, abundant availability, biodegradability and low cost. A series of chitosan–lignin (CL) composites were prepared through a hydrothermal method by varying the weight ratio of chitosan and lignin. Subsequently, these CL composites were combined with titania (T) to form a nanocomposite (T/CL) using sol–gel and hydrothermal based methods. T/CL nanocomposites exhibited improved photocatalytic performance in comparison with sol–gel and hydrothermally prepared pristine titania (SGH-TiO2), towards the selective oxidation of benzyl alcohol (BnOH) to benzaldehyde (Bnald) under UV (375 nm) and visible light (515 nm). More specifically, the 75T/CL(25 : 75) nanocomposite (a representative photocatalyst from the 75T/CL nanocomposite series) showed very high selectivity (94%) towards Bnald at 55% BnOH conversion under UV light. Whereas, SGH-TiO2 titania exhibited much lower (68%) selectivity for Bnald at similar BnOH conversion. Moreover, the 75T/CL(25 : 75) nanocomposite also showed excellent Bnald selectivity (100%) at moderate BnOH conversion (19%) under visible light. Whereas, SGH-TiO2 did not show any activity for BnOH oxidation under visible light. XPS studies suggest that the visible light activity of the 75T/CL(25 : 75) nanocomposite is possibly related to the doping of nitrogen into titania from chitosan. However, according to UV-visible-DRS results, no direct evidence pertaining to the decrease in band-gap energy of titania was found upon coupling with the CL composite and the visible light activity was attributed to N-doping of titania. Overall, it was found that T/CL nanocomposites enhanced the photocatalytic performance of titania via improved light harvesting and higher selectivity through mediation of active radical species.

While photocatalysis is considered a promising sustainable technology in the field of heterogeneous catalysis as well as biocatalysis, figures of merit (FOM) for comparing catalytic performance, especially between disciplines, are not well established. Here, photocatalytic water splitting was conducted using a semiconductor (NiO/La-NaTaO3) and a bio-photocatalyst (Synechocystis sp. PCC 6803) in the same setup under similar reaction conditions, eliminating the often ill-defined influence of the setup on the FOMs obtained. Comparing the results enables the critical evaluation of existing FOMs and a quantitative comparison of both photocatalytic systems. A single FOM is insufficient to compare the photocatalysts, instead a combination of multiple FOMs (reaction rate, photocatalytic space time yield and a redefined apparent quantum yield) is superior for assessing a variety of photocatalytic systems.

Applied catalysis / B 282, 119483 (2021). doi:10.1016/j.apcatb.2020.119483, Aiming at a better understanding of the role of electronic / chemical modifications of the support on the performance of high specific surface area Ru/TiO$_{2}$ catalysts in the selective CO methanation, we prepared and examined four different Ru/TiO$_{2}$ catalysts with similar Ru loading and similar high specific surface area, but with the support doped with different amounts of Si (0���12 wt.% SiO$_{2}$). Their activity for methane formation exhibits a volcano-shaped dependence on the SiO$_{2}$ content, with a maximum between 4 and 8 wt.%. The CO adsorption properties showed distinct differences, with the weakest CO adsorption strength for the most active catalysts. Based on the results of a variety of different characterization techniques and pyrrole/pyridine adsorption measurements, the higher activity / lower CO adsorption strength cannot be explained by a single property, such as particle size, but must rather be caused by a complex combination of different effects., Published by Elsevier, Amsterdam

Solar energy‐driven processes for biomass valorization are priority for the growing industrialized society. To address this challenge, efficient visible light‐active photocatalyst for the selective oxidation of biomass‐derived platform chemical is highly desirable. Herein, selective oxidation of 5‐hydroxymethylfurfural (HMF) to 2,5‐diformylfuran (DFF) was achieved by visible light‐driven photocatalysis over titania. Pristine titania is photocatalytically inactive under visible light, so an unconventional approach was employed for the visible light (λ=515 nm) sensitization of titania via a formation of a visible light‐absorbing complex of HMF (substrate) on the titania surface. Surface‐complexation of HMF on titania mediated ligand‐to‐metal charge transfer (LMCT) under visible light, which efficiently catalyzed the oxidation of HMF to DFF. A high DFF selectivity of 87 % was achieved with 59 % HMF conversion after 4 h of illumination. The apparent quantum yield obtained for DFF production was calculated to be 6.3 %. It was proposed that the dissociative interaction of hydroxyl groups of HMF and the titania surface is responsible for the surface‐complex formation. When the hydroxyl groups of titania were modified via surface‐fluorination or calcination the oxidation of HMF was inhibited under visible light, signifying that hydroxyl groups are decisive for photocatalytic activity., From ligand to metal: The selective oxidation of 5‐hydroxymethylfurfural (HMF) to 2,5‐diformylfuran (DFF) by visible light photocatalysis over titania is achieved with high DFF selectivity (87 %) at 59 % HMF conversion after 4 h of illumination. A complex of HMF on the titania surface acts as a sensitizer via a ligand‐to‐metal charge transfer (LMCT) under visible light.

Mesopores in the range of 4 to 5 nm were introduced into zeolite Y (nSi/nAl = 16) by surfactant-templating. This method using a mixture of octadecyltrimethylammonium hydroxide and bromide (C18TAOH/C18TABr) yields a mesoporous zeolite (Y–C18TAOH) with a higher specific mesopore volume and only a small loss in crystallinity and specific micropore volume. After loading with Pt, the two bifunctional catalysts (2.7Pt/Y and 2.6Pt/Y–C18TAOH) were applied in the aqueous-phase hydrogenation of levulinic acid (LA) to γ–valerolactone (GVL) (pH2 = 2.5 MPa, 393 K). Intraparticle mass–transfer limitations present for the catalyst 2.7Pt/Y were not observed in the LA hydrogenation over the catalyst with the hierarchical pore system 2.6Pt/Y–C18TAOH. Changes in the acid and de-/hydrogenation functionality are shown not to be responsible for the high catalytic activity of 2.6Pt/Y–C18TAOH. The presence of additional mesopores in a bifunctional catalyst based on zeolite Y is proven to enhance the mass-transfer properties and the resulting catalytic activity in the aqueous-phase hydrogenation of LA for the first time. Hue-Tong Vu is grateful to Vietnam International Education Development of the Ministry of Education and Training, Vietnam, for funding her doctoral study at Universität Leipzig, Germany. Noemi Linares and Javier García-Martínez acknowledge funding from the European Commission through the H2020-MSCA-RISE-2019 program (Ref. ZEOBIOCHEM – 872102) and the Spanish MINECO and AEI/FEDER, UE through the project RTI2018-099504-B-C21. Noemi Linares thanks the University of Alicante for funding (UATALENTO17-05).

MgO-ZrO2 as a support material for DRM catalysts was prepared with varying MgO-content (12–68 mol-%) relative to ZrO2. Characterizing the acid/base properties of MgO-ZrO2 materials with TPD-NH3 and TPD-CO2, the density of acid/base sites was found to significantly decrease with increasing calcination temperature (723 K or 1123 K). Nevertheless, in relation to the specific BET surface area, values are comparable for both calcination temperatures and both, acid/base sites. The impregnation of Ni only significantly influences the density of acid/basic sites if MgO-ZrO2 was treated at only 723 K. Regarding the Ni-species available, melt-impregnation seems more suitable for DRM catalysts than wet-impregnation. In terms of catalytic activity in the DRM, results from an earlier work have been revisited with regard to the influence of MgO-content and basic sites.

Novel bifunctional metal-loaded polymer&ndash, silica composite (PSC) catalysts were investigated in the hydrodeoxygenation (HDO) of 4-(2-furyl)-3-buten-2-one (FAc) as a model substance for furfural&ndash, acetone aldol condensation products. PSC catalysts were synthesized via a sol&ndash, gel method with different polymer contents and subsequently doped with different noble metals. The product composition of the HDO of FAc could be tuned by using catalysts with different polymer (i.e., acidic properties) and metal content (i.e., redox properties), showing the great potential of metal-loaded PSC materials as tunable catalysts in biomass conversions with complex reaction networks. Furthermore, high yields (&gt, 90%) of the fully hydrodeoxygenated product (n-octane) could be obtained using noble metal-loaded PSC catalysts in only 8 h of reaction time.

Using fiber optical components and assemblies for space flight applications brings several challenges for the design and the qualification process. Good knowledge of the system and environmental requirements is needed to derive design decisions and select suitable components for the fiber optical subsystem. Furthermore, the manufacturing process and integration limitations are providing additional constraints, which have to be considered at the beginning of the design phase. Besides Commercial off the shelf (COTS) components, custom made parts are often necessary.

The liquid-phase hydrogenation of toluene and other alkyl substituted benzene derivatives with different critical diameters was investigated over Pt-catalysts supported on spherical controlled pore glasses (CPGs) as model supports at 373 K in the batch mode. The effect of mass-transfer within the catalyst pores was studied by varying the pore width (4, 10, and 80 nm) and average grain size (18–150 μm) of the Pt/CPG catalysts. For toluene hydrogenation, internal mass-transfer limitations were absent (effectiveness factor >90%) only for catalysts with particle sizes below 25 μm and pore widths ≤10 nm or with a pore width of 80 nm and particle sizes around 75 μm, respectively. Effective diffusion coefficients obtained from initial reaction rates via the Thiele concept, e.g., 2.8 × 10−10 m2 s−1 for toluene over the catalyst with 10 nm pore width, were an order of magnitude lower than when determined by PFG-NMR. This difference was explained in terms of transport resistances such as surface barriers affecting the diffusivity assessment via the Thiele concept, while PFG-NMR measures intraparticle diffusion only.

The Meteosat Third Generation (MTG) program will ensure the continuity and enhancement of meteorological data from geostationary orbit as currently provided by the Meteosat Second Generation (MSG) system. OHB-Munich, as part of the core team consortium of the industrial prime contractor for the space segment Thales Alenia Space (France), is responsible for the Flexible Combined Imager – Telescope Assembly (FCI-TA) as well as the Infrared Sounder (IRS).

Hydrogenation of p-nitrophenol (PNP) to p-aminophenol (PAP) using NaBH4 as a reducing agent was studied as a test reaction for determining the catalytic activity of supported Pt catalysts. The initial reaction rate, which is accessible within less than 10 min via online UV-vis spectroscopy at room temperature, ambient pressure, and in water as solvent, was applied as measure for catalytic activity. For three Pt catalysts supported on porous SiO2, porous glass, and Al2O3, respectively, significant differences in the catalytic activity by almost one order of magnitude were observed. However, especially in the case of very active catalysts, limitations of the reaction by internal or external mass transfer have to be considered.

Die Hydrierung von p-Nitrophenol (PNP) zu p-Aminophenol (PAP) mit NaBH4 als Reduktionsmittel wurde als Testreaktion fur die Bestimmung der katalytischen Aktivitat von Platin-Tragerkatalysatoren untersucht. Als Mas fur die Aktivitat dient die Anfangsreaktionsgeschwindigkeit, die in weniger als 10 Minuten mittels Online-UV-vis-Spektroskopie bei Raumtemperatur und Umgebungsdruck in Wasser als Losungsmittel zuganglich ist. Fur drei Pt-Katalysatoren mit porosem SiO2, porosem Glas bzw. Al2O3 als Trager wurden deutliche Aktivitatsunterschiede beobachtet. Allerdings mussen vor allem bei sehr aktiven Katalysatoren mogliche Limitierungen der Umsetzung durch externe und interne Stofftransportvorgange berucksichtigt werden. The hydrogenation of p-nitrophenol (PNP) to p-aminophenol (PAP) using NaBH4 as a reducing agent was studied as a test reaction for determining the catalytic activity of supported Pt catalysts. The initial reaction rate, which is accessible within less than 10 minutes via online UV-vis spectroscopy at room temperature, ambient pressure and in water as a solvent, was used as measure for the catalytic activity. For three Pt catalysts supported on porous SiO2, porous glass and Al2O3, respectively, significant differences in the catalytic activity were observed. However, especially in case of very active catalysts, limitations of the reaction by internal or external mass transfer have to be considered.

The preparation of supported Pd nanoparticles on porous materials (Al-SBA-15 and Al-MCF) was successfully achieved using a simple, fast and efficient reactive milling (mechanochemical) method. Upon preparation, catalysts were characterized by N2 physisorption, elemental analysis, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The catalytic activity of different Pd/Al-SBA-15 and Pd/Al-MCF materials was investigated in the hydrogenation of p-nitrophenol (PNP) to p-aminophenol (PAP) using NaBH4 as a reducing agent. Significant differences in catalytic activity for the prepared catalysts were observed, with a superior catalytic activity of Pd/Al-MCF as compared to Pd/Al-SBA-15. Furthermore, investigations on external mass-transfer limitations of the reaction conducted with two selected supported Pd catalysts were conducted and discussed.

Chitosan-derived N-doped carbon materials are attractive candidates for the preparation of catalysts with a wide range of applications. Chitosan is a nitrogen rich (~7 wt.%) renewable biomass resou...

Correction for ‘Titania/chitosan–lignin nanocomposite as an efficient photocatalyst for the selective oxidation of benzyl alcohol under UV and visible light’ by Ayesha Khan et al., RSC Adv., 2021, 11, 34996–35010. DOI: 10.1039/D1RA06500A