Catalytic nanocomposites can be prepared via solvent-free methodologies using biomass-derived humin by-products and iron salts, found active in the conversion of isoeugenol to vanillin.
Abstract The effect of the isomorphous substitution of some of the Si atoms in ZSM‐5 by Ge atoms on the Brønsted acid strength has been investigated by i) DFT calculations on cluster models of the formula ((HO) 3 SiO) 3 ‐Al‐O(H)‐ T ‐(OSi(OH) 3 ) 3 , with T =Si or Ge, and ((HO) 3 SiO) 3 ‐Al‐O(H)‐Si‐(OGe(OH) 3 )(OSi(OH) 3 ) 2 , ii) a 31 P NMR study of zeolite samples contacted with trimethyl phosphine oxide probe molecules and iii) a X‐ray photoelectron spectroscopy (XPS) study of ZSM‐5 and Ge‐ZSM‐5 samples. The calculations reveal that the effect of Ge incorporation on the framework acidity strongly depends on the degree of substitution and on the exact T ‐atom positions that are occupied by Ge. High Ge concentrations allow for enhanced stabilisation of the deprotonated Ge‐ZSM‐5 through structural relaxation, resulting in a slightly higher acidity as compared to ZSM‐5. This structural relaxation is not achievable in Ge‐ZSM‐5 with a low Ge content, which therefore has a slightly lower acidity than ZSM‐5. The NMR study indicates no difference between the Brønsted acidity of ZSM‐5(47) and Ge(0.09)ZSM‐5(36). Instead, evidence for the presence of a substantial amount of GeOH groups in the Ge‐containing samples was obtained from the NMR results, which is consistent with earlier FTIR studies. The XPS results do not point to an effect of Ge on the framework acidity of ZSM‐5(47), instead, the results can be best interpreted by assuming the presence of additional GeOH and SiOH groups near the surface of the Ge(0.08)ZSM‐5(47) sample.
A series of photocatalysts consisting of C- and N-doped titanium dioxide (TiO2) nanoparticles highly dispersed and firmly embedded at the surface of a silica matrix were prepared using a novel synthesis method in which activated carbon has a double role: it acts as support for depositing the TiO2 nanoparticles and as hard template for generating a silica matrix that embeds them. Additionally, the use of activated carbon in combination with ammonia during the synthesis led to carbon and nitrogen doping of the TiO2 domains, which enhanced their absorption of radiation in the visible range. The combination of these features led to higher activity (i.e. higher removal % and TON) in the photocatalytic degradation of probe pollutants (phenol and rhodamine B) compared to the benchmark P25 TiO2 under UV and, even more markedly, under visible radiation. Particularly, the photocatalyst prepared with 10 wt% of TiO2 nanoparticles (10%TiO2[email protected]2) displayed much enhanced TON values under visible radiation compared to P25 TiO2 (a 12 times higher TON with rhodamine B, and an 8 times higher TON with phenol). The TON values are also significantly higher compared to any previously reported TiO2-SiO2 photocatalyst. The TiO2[email protected]2 photocatalysts can be effectively reused in consecutive runs. The photocatalytic activity of the prepared materials was correlated to their physicochemical properties by means of a thorough characterisation using a combination of techniques (XRD, ICP-OES, N2 physisorption, TEM, UV–vis, FT-IR and XPS).
Abstract Novel biomass‐derived porous carbons are attractive candidates for the preparation of carbon‐supported catalysts with a wide range of catalytic applications. Such carbonaceous catalysts are environmentally benign and could provide a cost‐competitive advantage as compared to existing heterogeneous catalysts. Tunable surface properties of carbon materials and excellent physical properties (e.g., hydrophobicity, chemically inert nature, etc.) are compatible with diverse catalysis reactions including organic transformations, as well as electro‐ and photochemical processes in aqueous solutions. This contribution provides an overview on the utilization of different biomass feedstocks and/or biomass‐derived precursors for the synthesis of carbonaceous materials to design advanced catalytic systems and their emerging applications in catalysis.
Hochgeschwindigkeitstechniken wurden bei der Synthese und Prüfung von Titankatalysatoren auf Silsesquioxan-Basis (siehe Bild) für die Epoxidierung von Alkenen eingesetzt. Bei der Optimierung der Kondensation von Silanen zu Silsesquioxanen mit offener Struktur kamen verschiedene Lösungsmittel und Organotrichlorsilane zum Einsatz. Diese schnelle und doch einfache Synthesemethode liefert Katalysatoren, deren Leistung ähnlich der der besten bisher untersuchten Titankatalysatoren auf Silsesquioxan-Basis ist.
The objective of this paper is to investigate the anti-knock quality of sugar-derived levulinic esters (methyl levulinate (ML) and ethyl levulinate (EL)) and cyclic ethers (furfuryl ethyl ether (FEE) and ethyl tetrahydrofurfuryl ether (ETE)). To this end, combustion experiments were carried out in both an engine and a constant volume autoignition device (modified ignition quality tester (IQT)). The results from both apparatuses demonstrate that ML, EL and FEE have superior anti-knock quality to the reference Euro95 gasoline. ETE, conversely, performed markedly worse than the reference fuel on both setups and might therefore be a more appropriate fuel additive for compression ignition engines. The main reason of the distinctions in anti-knock quality can be found in the molecular structure of the neat biofuels. ML and EL are levulinic esters, with a ketone (CO) functionality and an ester (C(O)–O) group on the carbon chain. They can readily produce stable intermediates during the auto-ignition process, thereby slowing down the overall reaction rate. The unsaturated cyclic ether (FEE) has very strong ring C–H bonds. However, the saturated cyclic ether (ETE) has weak ring C–H bonds, which facilitate more readily ring opening reactions. Ethyl side chains on the cyclic ethers further accelerate the reaction rate. Importantly for future research, our results suggest that the modified (IQT) and engine experiments are interchangeable setups with respect to qualitative anti-knock quality evaluation of novel compounds.
