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The direct stepwise transformation of CH4 to CH3OH over Cu-exchanged zeolites has been an intensively researched reaction as it can provide a solution for the utilization of this abundant feedstock. Up to date a commercial process is far from realization, which is why an understanding of the Cu speciation in zeolites as a function of reaction conditions as well as the development of a mechanistic view of the reaction are necessary to further advance the field. Herein we study Cu-exchanged ferrierite zeolite for the direct CH4 to CH3OH conversion by utilizing X-ray absorption spectroscopy (XAS), in order to assess the local structure and electronic properties of Cu through the reaction. A Cu-FER sample with a Cu/Al = 0.20 and Si/Al = 11 was subjected to three reaction cycles yielding ultimately 96 µmol C H 3 OH / g zeolite . Normalized to the Cu loading, this accounts for 0.33 mol C H 3 OH /molCu, making the sample comparable to very active Cu-MOR materials reported in the literature. During O2 activation, a transient self-reduction regime of CuII to CuI ions was identified; eventually leading to mostly framework interacting CuII species. CH4 loading leads to a reduction of these CuII containing species; which are finally partially reoxidized during H2O-assisted CH3OH extraction. The speciation after CH4 activation as well as H2O-assisted CH3OH extraction was assessed via linear combination fitting analysis of the XAS data. [ABSTRACT FROM AUTHOR]

Innovative processes for converting carbohydrates to materials and fuels form the basis for profitable bio-based economies of the future. For such innovation, approaches that provide detailed structural information would be desirable to detect uncharted chemistries of carbohydrate conversion. Among the most important value-added products accessible though conversion of biomass is 5-hydroxymethylfurfural (HMF), whose market values strongly depends on the quality of the product. Here, we use high-field in situ NMR spectroscopy to shed light on obscure competing reactions of CrCl3-catalyzed carbohydrate conversion to HMF in water. High-field NMR spectroscopy has enormous prowess in distinguishing isomeric and dehydrated products formed from glucose. Previously unidentified compounds were identified with this approach and include anhydrosugars and a variety of branched and linear mono- and disaccharides. Other identified compounds leverage the understanding of the active catalyst species. In addition to providing mechanistic insight, the approaches and findings described herein help to measure and manage carbon balances and product quality in HMF production. [ABSTRACT FROM AUTHOR]

Catalytic methane oxidation is used in exhaust gas after treatment to reduce methane emissions in stationary combustion processes as well as in natural gas vehicles. Pd/zeolite catalysts provide higher activity than the commonly used Pd/AlO, but suffer from rapid deactivation under reaction conditions and in the presence of steam. This work presents a detailed study of deactivation of 1 wt% Pd/H-ZSM-5 catalyst in reaction conditions in dry and wet feed including characterization of both the active phase and the support. Initially well-dispersed PdO particles are not stable and sinter immediately after the exposure to the reaction mixture even in dry feed and stabilize at lower dispersion level. Despite the reasonable methane oxidation activity exhibited by the large particles, the initial PdO particles could potentially provide a 40 °C lower methane oxidation temperature. In the presence of water in the feed at moderate temperature (450 °C), support degradation governs the deactivation of the catalyst, which is evidenced by a significant decrease in BET surface area and generation of extra-framework aluminium species. These results suggest that active and stable catalysts could be obtained by careful choice and design of the support material with the aim to guarantee high dispersion of PdO. [ABSTRACT FROM AUTHOR]

Engineering at the nanoscale level is a key aspect for the design of novel devices for sustainable energy to address the changeover from fossil fuels to renewable energy sources. This perspective paper, after introducing this topic, analyses the design and development of photoelectrocatalytic cells for producing solar fuels. To overcome limitations in the design of photoelectrocatalytic cells, a different one is proposed which eliminates the need of having a liquid electrolyte, where the electrodes are immersed. This cell design requires specific characteristics in the related electrodes/materials, which in combination with the different operation conditions, determine the need to investigate new fundamental aspects in the area. Some of the aspects analyzed regard (i) the role of nanostructure for visible light absorption of the semiconductor used, (ii) the need to use catalytic concepts (photoelectro-catalysis rather than photoelectro-chemistry), (iii) the mobility of charge carriers and relation with electrode characteristics, and (iv) space charge and Helmholtz layer. [ABSTRACT FROM AUTHOR]

A rationalized design of the organic structure directing agents (OSDAs) allows the preparation of zeolites with specific framework topologies, crystal sizes and/or chemical compositions. In the last years, organic molecules containing aromatic rings in their structures have been described as efficient OSDAs for the synthesis of zeolites with different physico-chemical properties. The unique ability of these aromatic molecules to form rigid and bulky OSDAs by supramolecular self-assembling of two organic molecules, mainly through π-π interactions, has allowed the synthesis of zeolites with large void volumes, controlled chemical distribution and/or high external surface areas. Along the present review, I would like to highlight the recent achievements reported in the literature using aromatic self-assembled bulky dimers as OSDAs for the synthesis of zeolites. [ABSTRACT FROM AUTHOR]

A system comprising two catalysts supported on mesoporous silica nanoparticles (MSNs) was employed to perform a sequence of two reactions in a single pot. Palladium nanoparticles catalyzed the oxidation of furfuryl alcohol with molecular oxygen at atmospheric pressure. The oxidation product, furfural, was then reacted with acetone via an aldol condensation catalyzed by amines supported on MSNs. Each reaction was first tested individually to establish optimal conditions. Both catalysts were then introduced into the same reactor under the proven conditions, and the entire reaction sequence was performed giving the desired product with high selectivity. The overall yield of the reaction sequence was highly dependent on the relative concentrations of the reactants in the mixture. [ABSTRACT FROM AUTHOR]

The production of furfural from the C monosaccharides xylose, arabinose and ribose, as well as from real biomass (corn fiber), was studied using H-Beta zeolite as catalyst in a monophasic system with the biomass-derived solvent, gamma-valerolactone. Due to the combination of Brønsted and Lewis acid sites on this catalyst (Brønsted:Lewis ratio = 1.66), H-Beta acts as a bifunctional catalyst, being able to isomerize (Lewis acid) and dehydrate (Brønsted acid) monosaccharides. The combination of Lewis and Brønsted acid functionality of H-Beta was shown to be effective for the isomerization of xylose and arabinose, followed by dehydration. While no advantages were found in the conversion of xylose, higher furfural yields were achieved from arabinose, using H-Beta, 73 %, compared to sulfuric acid (44 %) and Mordenite (49 %). The furfural yields from corn fiber for H-Beta, H-Mordenite and sulfuric acid were 62, 44, and 55 %, respectively, showing that H-Beta is particularly effective for conversion of this biomass feedstock composed of 45 wt% hemicellulose, of which 66 % is xylose and 33 % arabinose. [ABSTRACT FROM AUTHOR]

Three bulky organic cations, benzylmethylpyrrolidinium (BMP), ( S, S)-2-hydroxymethyl-1-benzyl-1-methylpyrrolidinium (BML) and benzylmethylhexamethyleniminium (BMH), were used in combination with the small cation tetramethylammonium (TMA) in the synthesis of zeolite materials. Two of them are distinguished by the number of carbon atoms forming the cyclic amine, which varies from 4 in BMP to 6 in BMH. In addition, a -CH-OH group has been introduced in the carbon atom belonging to the amine ring next to the nitrogen atom, to originate a chiral molecule, BML, the third SDA used in this work. It has been found that the combination of the small TMA with those three bulkier SDAs, promotes the crystallization of zeolite structures that contain cages and channels. BMP leads to the crystallization of the 10-ring zeolite ferrierite, where TMA is located inside the ferrierite cage. If the size of the N-cyclic amine moiety increases, the resulting cation cannot be accommodated in the relatively narrow 10-ring channels of ferrierite, and in these cases the zeolite MCM-22 crystallizes. This zeolite contains large cages whose cross section is delimited by a 12-ring, where both BMH and BML can be easily accommodated. In this system, cage-like, chlatrasil type structures often co-crystallize with the open structures, evidencing that an appropriate balance between TMA and the bulky SDA is required to achieve the crystallization of open-frameworks. When BMP is used, mixtures of structurally related ferrierite and cage-like RUB-10 are obtained if an excess of TMA is present in the synthesis gel, while MCM-22 crystallizes together with the structurally related cage-like MTN phase. [ABSTRACT FROM AUTHOR]

Extra-large pore germanosilicate zeolite with UTL structure was tested in the n-decane hydroisomerization/hydrocracking reaction. The product selectivity demonstrated UTL to be the most open zeolite material ever characterized with the decane test. Al- and B-containing samples were synthesized with high degree of crystallinity. The incorporation of part of the heteroelements was confirmed with Al and B NMR spectroscopy. The catalytic activity and the structural stability of these samples was significantly lower compared to germanosilicate UTL and followed the sequence: UTL > Al-UTL > B-UTL. [ABSTRACT FROM AUTHOR]

Modification of textural and chemical properties of SSZ-35 was investigated in respect to the catalytic behavior of this zeolite in p-xylene alkylation with isopropyl alcohol. Acidic treatment of the external surface of SSZ-35 crystals resulted in a decrease in the void volume of the zeolite and in the concentration of acid sites mainly located on the external surface. This was evidenced from the FTIR spectra of adsorbed pyridine and 2,6-di-tert-butylpyridine. The modification caused a significant increase in the selectivity to 2,5-dimethylcumene while the p-xylene conversion decreased only very slightly. [ABSTRACT FROM AUTHOR]

The skeletal isomerization of n-butenes to isobutene has been carried out over ferrierite catalysts (Si/Al ~ 15) containing different acid sites distribution and different amount of defects. The zeolite crystals were synthesized under hydrothermal conditions in fluoride medium in the absence of alkaline cations by using suitable combinations of structure directing agents. Template-driven low density of acid sites in 10-membered-ring channels enhances the isobutene selectivity and decreases catalyst deactivation. The presence of high amount of silanol groups and Lewis acid sites increases the yields of by-products and catalysts decay. [ABSTRACT FROM AUTHOR]