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 ...resource derived from seafood waste. Nitrogen-containing functional groups (amine and acetamide) of chitosan make it a suitable precursor for the synthesis of N-doped carbon materials. This perspective provides an overview on various techniques for the preparation and characterization of chitosan-based N-doped carbon materials and their application in the field of electrocatalysis and photocatalysis. Additional doping with nitrogen imparts greater electrochemical stability and basic character to the material due to the ability of nitrogen atoms to accept electrons. Nevertheless, each type of C–N bonding configuration has unique potential for catalytic reactions attributed to different electronic structure and catalytically active sites. The ability to acquire desired N-bonding states during the process of doping will provide a better control over the material application. The promising performance of chitosan-based N-doped carbon materials in electrocatalytic and photocatalytic reactions is attributed to their improved electronic structure and charge transfer properties. Moreover, research trends toward the design of chitosan-based N-doped carbons materials with required features for electrocatalytic and photocatalytic applications have also been identified.
The surge in biodiesel production in recent years has resulted in enhanced research interest in the conversion of glycerol to other valuable chemicals such as glycerol carbonate (GLC). In the present ...study, the catalytic transesterification of glycerol with dimethyl carbonate (DMC) for the production of GLC was studied with calcium–lanthanum mixed-oxide catalysts at different Ca/La molar ratios. These catalysts were synthesized using an exo- and endotemplating method. The physicochemical characteristics of the catalysts were determined using powder X-ray diffraction (XRD), N2 sorption, scanning electron microscopy (SEM), and temperature-programmed desorption (TPD) of CO2 and NH3. The transesterification of glycerol was found to be highly dependent on the basicity of the catalysts. The catalyst with a Ca/La molar ratio of 3 (3CaLa) showed the highest glycerol conversion and GLC yield. Optimization of the reaction parameters and reusability of the catalyst were studied with the 3CaLa catalyst in terms of glycerol conversion, GLC yield, and turnover frequency (TOF). At the optimum operating conditions, namely, a reaction time of 90 min, a DMC/glycerol molar ratio of 5, a catalyst mass of 0.217 g, and a temperature of 90 °C, the glycerol conversion and GLC yield were found to be 94% and 74%, respectively, with a reaction rate of ∼0.14 mol L–1 h–1 (with respect to glycerol).
The complexity of intimacy Glaser, Roger
Nature (London),
12/2015, Letnik:
528, Številka:
7581
Journal Article
Recenzirano
On page 245 of this issue, Zecevic et al.2 report a major breakthrough in the design of hydrocracking catalysts, which greatly improves the selectivity of the process so that more of the desired ...products are formed. The results shatter the belief that the noble-metal sites and the acid sites must be as close together as possible for effective catalysis.
Metal–organic frameworks represent a class of microporous adsorbents with high application potential for adsorption heat transformation. Here, we present a functional, full-scale heat exchanger ...coated with the microporous aluminum fumarate MOF Basolite A520 using a polysiloxane-based binding agent. The function of the heat exchanger was evaluated resulting in a gross cooling power of 2900 W (at the beginning of the adsorption cycle) or, respectively an average cooling power of 690 W (up to a limit of 90% equilibrium loading in 7 min) under the working conditions of a realistic adsorption chiller of 90 °C – 30 °C – 18 °C (temperature level of heat source, heat rejection/condenser, and evaporator).
In the future, (electro‐)chemical catalysts will have to be more tolerant towards a varying supply of energy and raw materials. This is mainly due to the fluctuating nature of renewable energies. For ...example, power‐to‐chemical processes require a shift from steady‐state operation towards operation under dynamic reaction conditions. This brings along a number of demands for the design of both catalysts and reactors, because it is well‐known that the structure of catalysts is very dynamic. However, in‐depth studies of catalysts and catalytic reactors under such transient conditions have only started recently. This requires studies and advances in the fields of 1) operando spectroscopy including time‐resolved methods, 2) theory with predictive quality, 3) kinetic modelling, 4) design of catalysts by appropriate preparation concepts, and 5) novel/modular reactor designs. An intensive exchange between these scientific disciplines will enable a substantial gain of fundamental knowledge which is urgently required. This concept article highlights recent developments, challenges, and future directions for understanding catalysts under dynamic reaction conditions.
Dynamic times: In the future, (electro‐)chemical catalysts will have to be more tolerant towards a varying supply of energy and raw materials caused by fluctuating renewable energy sources. To stimulate in‐depth studies of catalysts and catalytic reactors under such transient conditions, this concept article highlights corresponding developments, challenges, and future directions.
Chiral phosphoric acids (CPAs) are among the most frequently used organocatalysts, with an ever-increasing number of applications. However, these catalysts are only obtained in a multistep synthesis ...and are poorly recyclable, which significantly deteriorates their environmental and economic performance. We herein report a conceptually different, general strategy for the direct immobilization of CPAs on a broad scope of solid supports including silica, polystyrene, and aluminum oxide. Solid-state catalysts were obtained in high yields and thoroughly characterized with elemental analysis by inductively coupled plasma-optical emission spectrometry (ICP-OES), nitrogen sorption measurements, thermogravimetric analysis, scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy (STEM/EDX) images, and solid-state NMR spectroscopy. Further, the immobilized catalysts were applied to a variety of synthetically valuable, highly stereoselective transformations under batch and flow conditions including transfer hydrogenations, a Friedländer condensation/transfer hydrogenation sequence, and Mannich reactions under cryogenic flow conditions. Generally, high yields and stereoselectivities were observed along with robust catalyst stability and reusability. After being used for 10 runs under batch conditions, no loss of selectivity or catalytic activity was observed. Under continuous-flow conditions, the heterogeneous system was in operation for 19 h and the high enantioselectivity remained unchanged throughout the entire process. We expect our approach to extend the applicability of CPAs to a higher level, with a focus on flow chemistry and a more environmentally friendly and resource-efficient use of these powerful catalysts.
In-situ growth of supported embryonic TS-1 zeolite (<10 nm) on a silica support was achieved by steam-assisted crystallization (SAC). The use of low amounts of TPABr and steam at a moderate ...temperature of 130 °C was the key factor to control partial transformation of silica into supported embryonic TS-1. Compared with the reference crystalline TS-1, supported embryonic TS-1 exhibits a higher activity in dibenzothiophene (DBT) oxidation (TOF: 8–275 h–1 vs 2.7–160 h–1 at 30–98 °C), a higher resistance to poisoning by nitrogen-containing compounds, and a higher selectivity (>97%) in the productive utilization of the oxidant in DBT oxidation. The activity of the amorphous titanosilicate (TOF: 21.2–210 h–1 at 30–80 °C), the solid precursor of the SAC process, was higher than that of the embryonic and the crystalline TS-1. The analysis of the structural properties–catalytic performance of these catalysts showed an improved accessibility to defective Ti active sites “Ti(OH)(OSi)3” with higher catalytic activity. The results of this study should be encouraging to unearth many other active amorphous catalysts with the potential of industrial application.
A dealuminated Y-zeolite with a nSi/nAl ratio of 130 is treated in pure water and aqueous solutions of NaCl at different pH values between 3 and 7 at 100 °C for up to 3 weeks. The change of specific ...micropore volume, the specific external surface, and the mesopore size distribution are monitored by N2-adsorption (77 K). The decrease of micropore volume proceeds due to a zero order kinetics. The zeolite loses no mass, but according to an XRD analysis the loss of micropore volume is paralleled by the formation of mainly amorphous material. The amorphization is assumed to start at the outer surface of the zeolite crystals leading to a core-shell distribution of amorphous and zeolitic material. The amorphization is coupled with the formation of mesopores and an increasing external surface area. The evolution of mesopores mainly occurs at diameters near the lower boundary region of the pore size analysis by N2 sorption (3 nm). The degradation is catalyzed by hydroxide ions present in bulk water. Both the exchange of the acidic protons with Na+-ions and the presence of NaCl in the water phase accelerate the degradation at pH 7. The zeolite is decomposed in 1 M NaCl at pH 7 and 100 °C within 40 min. However, when the pH is lowered to 3, it is stable in 1 M NaCl for more than 10 days. The protonated form in pure water is about half as stable as the Na+-form in 1 M NaCl at pH 3.
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•Extremely unstable in 1 M NaCl at pH 7.•Extremely stable in 1 M NaCl at pH 3.•H+-form in water somewhat less stable than in 1M NaCl at pH 3.•Decrease of micropores follows a zero order type reaction.
In this study, the adsorption of CO2 and H2S has been investigated on commercial activated carbon Desorex K43 impregnated with K2CO3, NaOH, or Fe2O3 in order to assess their potential for “upgrading” ...and desulfurization of biogas or contaminated natural gas. Different chemical Fourier transformed infrared spectra (FTIR), X-ray fluorescence (XRF) and pH measurements and textural characterization techniques (N2 adsorption/desorption isotherms) were used to study the material surface and confirm the presence of K, Na, and Fe. Gravimetric experiments of single and binary gas sorption isotherms were used to evaluate CO2 uptake and selectivity with respect to CH4. Breakthrough curves under dry and humid conditions were performed to assess the adsorption of H2S. The materials studied showed high adsorption capacities for both gases: in the range from 0.85 to 4.58 mmol g–1 for H2S and from 1.61 to 1.88 mmol g–1 CO2, under dry conditions and 1 bar. Furthermore, the selectivity of the activated carbons for CO2 in relation to CH4 was in the range of 1.2–2.4, Desorex K43-BG being the material with higher adsorption capacity for gases under study. The data obtained by the adsorption experiments were correlated with the textural characteristics and the chemical properties of the materials, which allowed one to identify how promising an adsorbent is for the removal of acidic gases from biogas to obtain biomethane. The best compromise between H2S adsorption and CO2/CH4 selectivity was found for the sample containing Na (Desorex K43-Na), which benefited from both a basic surface chemistry and pore size distribution restricted to the micropore range.
The demand for cooling devices has increased during the last years and this trend will continue. Adsorption‐driven chillers (ADCs) using water as the working fluid and low temperature waste energy ...for regeneration are an environmentally friendly alternative to currently employed cooling devices and can concurrently help to dramatically decrease energy consumption. Due to the ideal water sorption behavior and proven lifetime stability of Al(OH)(m‐BDC) ∙ x H2O (m‐BDC2− = 1,3‐benzenedicarboxylate), also denoted CAU‐10‐H, a green very robust synthesis process under reflux, with high yields up to 95% is developed and scaled up to 12 kg‐scale. Shaping of the adsorbent is demonstrated, which is important for an application. Thus monoliths and coatings of CAU‐10‐H are produced using a water‐based binder. The composites are thoroughly characterized toward their mechanical stability and water sorption behavior. Finally a full‐scale heat exchanger is coated and tested under ADC working conditions. Fast adsorption dynamic leads to a high power output and a good power density. A low regeneration temperature of only 70 °C is demonstrated, allowing the use of low temperature sources like waste heat and solar thermal collectors.
Metal–organic frameworks (MOFs) can be implemented as active materials in adsorption‐driven chillers. Therefore a green robust synthesis for the Al‐MOF CAU‐10‐H, scalable to 12 kg‐scale, is developed. Monoliths and coatings are produced using a water‐based binder and are investigated as composite material. Finally a full‐scale heat exchanger is coated and measured under adsorption‐driven chiller working conditions.
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