Gambo, YahyaAdamu, SagirLucky, Rahima A.Ba-Shammakh, Mohammed S....
23页
查看更多>>摘要：The design and development of novel tandem catalysts to facilitate the production of value-added chemicals and fuels via heterogeneous routes holds great prospect in revolutionizing the chemical industry. Herein, we discuss the fundamentals of tandem catalysis and provided a comprehensive account of recent advances related to the design and tuning of tandem catalysts for direct CO2 hydrogenation to light olefins. Moreover, insights on catalyst deactivation in tandem CO2 hydrogenation has been provided. In addition, the prospects of core-shell configuration and its high flexibility in implementing efficient tandem catalyst design strategies has been discussed. Most importantly, the insights and perspectives provided therein are hoped to stimulate and guide in the future design of highly efficient tandem catalysts that could enable the commercialization of the process as a sustainable and environmentally benign alternative for olefin production.
查看更多>>摘要：Knoevenagel condensation reaction is an important reaction for the manufacture of alpha,13-unsaturated carbonyl compounds. Traditional base catalysts suffer from the disadvantage in catalyst-product separation. Herein, potassium-doped carbon nitride materials supported on SBA-15 (CN/SBA15-KCl) have been prepared through a one-pot calcination method. The characterization results of N2 adsorption-desorption, small-angle XRD, TEM, and SEM revealed that the ordered mesostructures of SBA-15 had been preserved after the loading of carbon nitride and KCl, and nitrogen and potassium species were dispersed on the surface of SBA-15 support. As solid bases, the CN/SBA15-KCl materials demonstrated high and steady catalytic performances in Knoevenagel condensation. Under 50 degrees C of reaction temperature, the optimized conversion of benzaldehyde was up to 74% at 4 h of reaction time, much higher than other carbon-nitride-based materials. The incorporation of potassium has been proved to enhance the basic strength of CN/SBA15, and therefore improved the catalytic activity.
查看更多>>摘要：Direct CO2 hydrogenation into linear alpha-olefins presents a promising route in carbon-neutral chemical manufacture. This work systematically investigated the variable interplay between Reverse Water-Gas Shift (RWGS) and Fischer-Tropsch Synthesis (FTS) during CO2 hydrogenation using model Na-Fe5C2 catalysts, combining dynamic/steady-state CO/CO2 hydrogenation performance, intrinsic kinetics and multiple characterization results. Na-Fe5C2 proves to be surface-enriched with FeOx sites over which RWGS readily proceeds. Meanwhile, CO2 conversion under integral reaction conditions is limited by the subsequent FTS step due to a lack of available FeCx sites. The catalyst performance is steered by the properties and relative quantities of the two different active sites. Na addition promotes the refresh of FeOx sites and beta-elimination of alkyl intermediates over FeCx sites, but at the cost of inhibiting the surface fraction of FeCx sites and thus the single-pass CO2 conversion. These fundamental understandings will enlighten further development of CO2 hydrogenation catalysts with improved hydrocarbon yields.
查看更多>>摘要：Sb doped cryptomelane-type manganese oxides (Sb-OMS-2) with Sb/Mn molar ratios of 0-0.4 were synthesized and investigated for low-temperature selective catalytic reduction of NO by CO (CO-SCR). The resulting catalyst was characterized by X-ray diffractometer (XRD), specific surface area analyzer (BET), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). As a result, the doping of Sb increased the specific surface area and oxygen vacancy concentration of the catalyst. At the same time, most Sb entered the lattice of MnO(6 )to form Sb-O bonds, and a small number of Sb ions replaced K+ in the tunnel. Sb and Mn synergistically catalyzed the reduction of NO. Compared with undoped OMS-2, the NO conversion rate of Sb-0.2-OMS-2 increased from 60% at 150 C to 83%, and from 80% at 300 C to 95%. In the presence of SO2, the NO conversion rate of Sb0.2-OMS-2 at 300 C was 88%, while that of OMS-2 was only 60%.
查看更多>>摘要：Fe4O3@SiO2 supported vanadium-substituted polyoxometalates were fabricated and applied as catalysts for components separation from corncob in choline chloride-lactic acid (CC-LA) 1:10 (molar ratio) reaction system. PMoV3-Fe4O3 @SiO2 was selected as the optimal catalyst based on its performance in component separation process. The optimal temperature decreased from 150 ? to 120 ? with the application of catalyst. Under 120 ?, the application of catalyst can enhance the extraction percentage from 71.65% to 92.40% under the same reaction conditions. The purities of the lignin fractions are increased from 85.62% to 97.07%. But the difference between the M-w and M-n for the lignin fractions derived from the two reaction systems is quite gentle. Meanwhile, the components of the filtrates obtained under the catalyst supplemented system showed higher dissolved saccharides percentage compared with catalyst free system, and no lignin was detected. The residuals achieved by catalyst supplemented system showed high purity compared with the catalyst free system. The delignification kinetics for both reaction systems are more satisfied with pseudo-first-order kinetic model. The activation energy (E-a) could also decrease from 31.95 kJ & BULL;mol(-1) to 18.86 kJ & BULL;mol(-1). The catalyst was easily separated from DESs due to its magnetic property and showed excellent reusability. The possible reaction mechanism was proposed to benefit the refining of biomaterials.
Teles, Camila A.Ciotonea, CarmenGomes, NicolasGoncalves, Vinicius O. O....
11页
查看更多>>摘要：The effect of aluminium content (x = 5, 20 and 40 wt %) in SBA-15 type silica supports used to obtain Pd/xAl-SBA-15 catalysts was evaluated in the HDO reaction of m-cresol at 300 degrees C, under atmospheric and high (30 bar) pressure. Aluminium incorporation was performed using the two-step pH-adjustment method, affording the deposition of Al phases over silica previously precipitated. Pd was thereafter deposed using incipient wetness impregnation. Physico-chemical properties of the catalysts were investigated by XRD, N-2 physisorption, H-2 chemisorption, DRIFTS of adsorbed pyridine, STEM-EDX mapping coupled to HAADF imaging. The acidity (Bronsted and Lewis sites) generated by the incorporation of aluminium at low content (i.e. 5 wt %) onto the SBA-15 structure resulted in the improvement of HDO of m-cresol, with an increase in selectivity toward the deoxygenated products, toluene under atmospheric pressure (38 % for the Pd/SBA vs. 77 % for the Pd/Al5-SBA) and methylcyclohexane under high pressure (14 % for the Pd/SBA vs. 30 % for Pd/Al5-SBA). The selectivity into methylcyclohexanone was also affected by the total pressure: 5 % under atmospheric pressure vs 64 % under 30 bar over Pd/Al5-SBA). However, under atmospheric pressure, at higher Al contents, side reactions catalyzed by acid sites were promoted, such as isomerization and disproportionation reactions, which were not observed under high pressure. Besides that, the increase of quantity of Al leaded to the decrease of the surface accessibility and hence drop on the reactions rate over both pressure conditions. This work demonstrated the efficiency of Pd catalyst in HDO reaction which can be obtained by a precise adjustment of the quantity of Al in the SBA catalytic support.
查看更多>>摘要：As a salt of cyameluric acid and a derivative of tri-s-triazine, rod-shaped potassium cyamelurate K-3[C6N7O3] has been synthesized and employed as a homogeneous photocatalyst for photodegradation of aquatic tetracycline hydrochloride (TC-HCl) under visible-light irradiation for the first time. The water-soluble K3[C6N7O3] owns excellent visible-light-driven photocatalytic activity, which is approximately 9 and 10 times higher than those on melon and g-C3N4 in water, respectively. The photocatalytic process is investigated experimentally and theoretically, and the active centers of K-3[C6N7O3] are identified by first principles calculations. The active radicals for the photodegradation are identified and a reaction mechanism is proposed. Moreover, K-3[C6N7O3] can also work as an efficiently heterogeneous photocatalyst for the removal of TC-HCl in ethanol. This work provides a novel photocatalyst bridging homogenous and heterogeneous photocatalysis for environmental protection and opens a new application space for alkali cyanurates.
查看更多>>摘要：The application of deep eutectic solvents (DESs) in the catalytic degradation of polyethylene terephthalate (PET) has attracted increasing attention due to the high efficiency, biodegradability, and low toxicity of DESs. How-ever, the relationship between the structure and activity of DESs is still ambiguous. Herein, we report an efficient 1,5,7-triazabicyclo[4.4.0]decium acetate/zinc acetate (HTBD-OAc/Zn(OAc)(2)) DES catalyst for recycling waste PET based on a combination of experimental and theoretical studies. First, the HTBD-OAc/Zn(OAc)(2) DES structure, in which the HTBD-OAc moiety and Zn(OAc)(2) were connected through a N-H-O hydrogen bonding interaction, was clearly determined through theoretical calculations and experimental verification. Then, the HTBD-OAc/Zn(OAc)(2) was found to be effective for waste PET glycolysis, where the PET conversion reached 100%, and the bis(hydroxyalkyl) terephthalate (BHET) yield reached 88.5% at 190 C within 40 min in atmosphere. Additionally, the catalyst had high reuse performance; BHET yield remained 84.6% after the catalyst was used for over seven cycles. Density functional theory (DFT) calculations demonstrated that the PET glycolysis reaction mediated by the HTBD-OAc/Zn(OAc)(2) DES included two stages, and the 1,5,7-triazabicyclo[4.4.0]decium cation (HTBD) played a crucial role. In the first stage, the active species [Zn]-OCH2CH2OH anion was generated through proton transfer from HTBD to OAc-, which was followed by HOCH2CH2O-H bond activation through the cooperation of HTBD and Zn. In the second stage, catalytic depolymerization of PET occurred through the cooperative functions of the Zn center and HOCH2CH2O- anion ligand.
查看更多>>摘要：Nicotinamide adenine dinucleotide (NADH) is an essential coenzyme for many oxidoreductases in enzyme-catalyzed reactions. However, the reuse of NADH is necessary owing to its high price and high consumption. By mimicking the photosynthesis and leaf structure of plants, we designed a biomimetic leaf microreactor consisting of glass and waterproof double-sided tape for artificial photosynthesis. The glass substrates of the microreactor mimic the cuticle of the leaf epidermal cells to avoid water evaporation. In addition, the high flexibility of the waterproof double-sided tape makes it possible to prepare microreactors rapidly, without the constraints of expensive molds and materials. Moreover, the waterproof double-sided tape makes it easy and fast to combine the microchamber with the glass substrates without plasma bonding. The regeneration ratio of NADH in the biomimetic leaf microreactor reached 87.19%. To further increase the throughput, we propose a concept of a "leaf mosaic " microreactor array based on the leaf mosaic structure of plants.
查看更多>>摘要：To clarify the relationship between the structure and performance for the Ir-based catalysts, a series of Ir/SiO2 catalysts were prepared by the colloid-impregnation method and evaluated in the lean methane oxidation at low temperature. The results indicate that the colloid-impregnation is effective to attain highly dispersed Ir nanoparticles on the SiO2 support. The catalytic activity of Ir/SiO2 is sensitive to the structure and state of loaded Ir species; the Ir/SiO2 catalyst with abundant defective Ir3+ species and mean Ir particle size below 2.0 nm exhibits extraordinarily high activity in methane oxidation. However, the activity of Ir/SiO2 decreases considerably with the increase of calcination temperature, due to the agglomeration of Ir particles induced by high temperature. Nevertheless, the thermal stability of supported Ir catalysts can be greatly improved by employing proper support with strengthened metal-support interaction, suggesting the enormous potential of supported Ir catalysts in the related applications.
NSTL
Elsevier