The hydration of dimethyl ether (DME) to methanol over various solid acids was studied. The acidity of the catalysts is determined
by FTIR spectroscopy. The hydration is found to occur predominantly on the Br?nsted acid sites. Among the catalysts studied,
WOx/ZrO2 and H-ZSM-5 appeared to be most active and selective. 相似文献
Replacing fossil fuels with biodiesel enables the emission of greenhouse gases to be decreased and reduces dependence on fossil fuels in countries with poor natural resources. Biodiesel can be produced by an esterification reaction between free fatty acids (FFAs) and methanol or by transesterification of triglycerides from oils. Both reactions require homogeneous or heterogeneous catalysis. Production of biodiesel catalyzed by heterogeneous catalysts seems to be the preferred route, enabling easy product separation. As we have previously shown, the Lewis acids AlCl3 and BF3 can serve as highly efficient catalysts under ultrasonic activation. The present study focused on the development of oleic acid (OA) esterification with methanol by the same catalysts immobilized in silica matrices using the sol–gel synthesis route. During the course of immobilization, AlCl3 converts to AlCl3 × 6H2O (aluminite) and BF3 is hydrolyzed with the production of B2O3. The immobilized catalysts can be reused or involved in a continuous process. The possibility of biodiesel production using immobilized catalysts under ultrasonic activation is shown for the conversion of FFAs into biodiesel in batch and continuous mode. 相似文献
The energetically viable fabrication of stable and highly efficient solid acid catalysts is one of the key steps in large-scale transformation processes of biomass resources. Herein, the covalent modification of the classical Dawson polyoxometalate (POMs) with sulfonic acids (-SO3H) is reported by grafting sulfonic acid groups on the POM's surface followed by oxidation of (3-mercaptopropyl)trimethoxysilane. The acidity of TBA6-P2W17-SO3H (TBA=tetrabutyl ammonium) has been demonstrated by using 31P NMR spectroscopy, clearly indicating the presence of strong Brønsted acid sites. The presence of TBA counterions renders the solid acid catalyst as a promising candidate for phase transfer catalytic processes. The TBA6-P2W17-SO3H shows remarkable activity and selectivity, excellent stability, and great substrate compatibility for the esterification of free fatty acids (FFA) with methanol and conversion into biodiesel at 70 °C with >98 % conversion of oleic acid in 20 min. The excellent catalytic performance can be attributed to the formation of a catalytically active emulsion, which results in a uniform catalytic behavior during the reaction, leading to efficient interaction between the substrate and the active sites of the catalyst. Most importantly, the catalyst can be easily recovered and reused without any loss of its catalytic activity owing to its excellent phase transfer properties. This work offers an efficient and cost-effective strategy for large-scale biomass conversion applications. 相似文献
The Koch-type carbonylation of tert-butyl alcohol was studied over H-type zeolites. It was found that the catalytic carbonylation of a large amount of tert-butyl alcohol relative to the acidic sites of the H-zeolites in organic solvents requires an elevated temperature and CO pressure, although previous solid state NMR studies have revealed that the transformation of tert-butyl alcohol of an amount comparable to the acidic sites into 2,2-dimethylpropanoic acid proceeds just upon the CO co-adsorption in the H-zeolites at room temperature and atmospheric pressure. The catalytic performance of different H-zeolites and the influence of CO pressure, H2O addition and solvent effects on the carbonylation of tert-butyl alcohol have been investigated. H-ZSM-5 gives the highest selectivity for 2,2-dimethylpropanoic acid due to its adequate pore dimensions. The present work indicates the possible industrial application of solid acids as carbonylation catalysts instead of liquid acids for the Koch reaction to produce tert-carboxylic acids. 相似文献
Lignosulfonate (LS) is an organic waste generated as a byproduct of the cooking process in sulfite pulping in the manufacture of paper. In this paper, LS was used as an anionic supporting material for immobilizing cationic species, which can then be used as heterogeneous catalysts in some organic transformations. With this strategy, three lignin‐supported catalysts were prepared including 1) lignin‐SO3Sc(OTf)2, 2) lignin‐SO3Cu(OTf), and 3) lignin‐IL@NH2 (IL=ionic liquid). These solid materials were then examined in many organic transformations. It was finally found that, compared with its homogeneous counterpart as well as some other solid catalysts that are prepared by using different supports with the same metal or catalytically active species, the lignin‐supported catalysts showed better performance in these reactions not only in terms of activity but also with regard to recyclability. 相似文献
Water, as a byproduct in esterification, tends to adsorb on solid acid catalysts, causing loss of active components or decomposition of framework and thereby decreasing their reactivity and durability, while the development of water-tolerant solid acids is expected to solve these problems. In this review, the recent developments of major kinds of water-tolerant solid acids including zeolite, mesoporous silica, metal organic framework-based catalyst, magnetic nanoparticles, and polymeric catalyst are discussed in detail. Special attention has been paid to understand the role of hydrophobicity, acid strength, and structure of water-tolerant solid acids in catalytic performance and their stability. From the literature survey, it is found that despite the modified zeolites have a water contact angle as large as 160°, but their acid strength need to be improved and their small micropore sizes restrict their use in catalyzing the esterification of bulky molecules. In contrast, solid acids with abundant acid sites, suitable hydrophobicity, and abundant mesopores or macropores usually exhibit high activity and reusability. Among all the known solid acids, polystyrene-supported acidic ionic liquid catalysts (PS-CH2-[SO3H-pIM] [HSO4]) show a high yield of n-butyl acetate with 99.1% and high reusability of 13 times, which is a breakthrough over the traditional. This review aims to offer a comprehensive understanding for the water-tolerant solid acid catalysts in esterification.
Silica sol-gel entrapped acids, bases and organometallic catalysts are used successfully in one-pot reactions without interfering with each other. Both physically and covalently entrapped acids and bases were employed in these processes, including polystyrene sulfonic acid, 1-propane sulfonic acid, molybdosilicic acid (SiO2-MoO3), poly[(vinylbenzyltrimethyl)ammonium] hydroxide and 1,5,7-triazabicyclo[4.4.0]decene. The entrapped metal-based catalysts are Rh2Co2(CO)12 and RuCl2(PPh3)3. The one-pot reactions carried out with these heterogenized reagents and catalysts include formation of alkenes under acidic and basic conditions, C—C bond formation by condensation reactions with an -carbon to a carbonyl, hydroformylation and hydrogenation. 相似文献
Acylation of anisole and 3-methylanisole was performed with several acylating reagents (acetylation by AcCl and Ac2O and bromoacetylation by BrAcCl and (BrAc)2O) over different solid acid catalysts. The reaction conditions were optimized with respect to the acylation reagent, overall
yield, solid acid catalyst, and the products selectivities. While acylation of anisole with acetyl chloride or acetic anhydride
resulted in its full conversion to para-substituted acetophenone, the use of bromoacetyl bromide or bromoacetic anhydride yielded also the ortho-substituted product. Acylation of 3-methylanisole also yielded both para- and ortho-substitutions, and the products distribution was affected by the reaction conditions and catalyst type. It was found that
while more acidic catalysts (caesium salt of heteropolyacid and zeolites) were the most active towards anisole acylation,
the most active catalysts for the acylation of 3-methylanisole were ion-exchange catalysts. Employing HY-740 zeolite resulted
in the highest ortho-selectivity in the acylation of anisole with bromoacetyl bromide and bromoacetic anhydride and in the acylation of 3-methylanisole
with acetic anhydride. 相似文献
A green and effective approach for comprehensive hydrolyzation of cellulose has been described. Several carbon-based solid acids were successfully prepared using various biomass (glucose, microcrystalline cellulose, bamboo, and rice husk) and used to catalyze cellulose hydrolysis. The acid groups (–SO3H and –COOH) were successfully introduced onto the surface of the carbon-based solid acid catalysts as evidenced by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The structure of the prepared catalysts was characterized by scanning electron microscope and X-ray diffraction. The catalysts showed excellent catalytic performance for hydrolysis of cellulose. To improve the reaction efficiency, ball-milling and solubilization in ionic liquids of cellulose were adopted. A maximum total reducing sugar yield of 81.8 % was obtained in ionic liquid 1-butyl-3-methyl imidazolium chloride at 125 °C for 90 min when the water addition was 10 % of ionic liquid. This study provided a promising strategy to synthesize solid acids from lignocelluloses, which were further used to convert biomass into biofuels and platform chemicals. 相似文献
Porous inorganic-organic hybrids have been prepared by the reaction of 4,4′-biphenylbis(phosphonic acid) with Zr(IV) in organic solvents. The resultant products consist of α-zirconium phosphate-type layers crosslinked by biphenyl pillars. By using an excess of Zr in the synthesis, surface areas of ∼400 m2/g have been obtained and the pores can be controlled to be the micro-type with diameters of 10-20 Å and a relatively narrow pore size distribution. The aromatic rings are readily sulfonated by SO3 under pressure to produce very strong Bronsted acid catalysts. An NMR procedure, utilizing the shift of the carbonyl carbon of acetone-2-13C sorbed onto the sulfonated products, indicated an acid strength for the Bronsted acid sites equal to that of 100% sulfuric acid. Unpillared Zr(O3PC6H4SO3H)2 has a somewhat lower acid strength, but still has a higher acid strength than zeolites HX and HY. The particles of this layered acid exfoliate in water and light-scattering data show that they are in 5 nm size range. They also exhibit high proton conductivity as solid membranes. These sulfonated materials have a potential as strong acid catalysts for a variety of reactions at a low temperature. 相似文献