The contribution of the methanol-to-aromatics reaction to benzene methylation over ZSM-5 catalysts

The methanol to aromatics conversion is shown to contribute significantly to the benzene methylation with methanol at 400 °C over acidic ZSM-5 catalysts but such contribution over all catalysts is negligible at 250 °C. Benzene-only conversion shows only negligible contribution at both temperatures over the catalysts studied. However, it appears that the methanol-only conversion can be minimised, to enhance the benzene methylation with methanol (and indirectly the oxidative benzene methylation with methane), by using NaZSM-5 with highly reduced Brönsted acidity.     

Synthesis of acrolein by gas‐phase dehydration of glycerol over silica supported Bronsted acidic ionic liquid catalysts

BACKGROUND: Glycerol has become readily available as a byproduct from the biodiesel industry. High functionality and relatively low price make it a potential building block to produce value‐added derivatives such as acrolein. RESULTS: Dehydration of glycerol to acrolein was performed over several silica supported Brønsted acidic ionic liquids as catalysts. All the catalysts prepared were active for the synthesis of acrolein (conversion of glycerol was observed in the range 35–90% with selectivity to acrolein in the range 29–58%). CONCLUSIONS: Catalyst prepared from triphenyl (3‐sulfopropyl) phosphonium 4‐methylbenzenesulfonate gave good activity and selectivity at 4 h reaction time. The conversion of glycerol decreased with increase in glycerol concentration. Higher temperature (325 °C) resulted in significantly lower conversion as well as selectivity to acrolein. With the use of two additional traps cooled to ? 7 °C, the selectivity to acrolein increased significantly for good catalysts. Copyright © 2010 Society of Chemical Industry     

Catalytic Etherification of Glycerol to Diglycerol Over Heterogeneous Calcium-Based Mixed-Oxide Catalyst: Reusability and Stability

The activities of different heterogeneous alkaline-earth metal oxide catalysts and mixed-metal oxide catalysts were investigated. Glycerol etherification was carried out at 250°C in a three-necked glass reactor vessel at atmospheric pressure. In a typical experiment, 50 g of anhydrous glycerol was loaded into the reactor. Then, 2 wt.% of catalyst was added to the reactor. The reactor was then heated to the appropriate reaction temperature in nitrogen atmosphere under continuous stirring. The heterogeneous CaO catalyst showed the highest catalytic conversion (72%) compared with other alkaline-earth metal oxides, with a diglycerol yield of 19%. The highest glycerol conversion of 96% and diglycerol yield of 52% were observed for the mixed-metal oxide catalyst (Ca_1.6Al_0.4La_0.6O₃). Reusability and stability of this catalyst were tested. The ICP-AES analysis was performed to confirm the leaching of the metal species in the liquid phase of the reaction mixture.     

Exploratory Catalyst Screening Studies on the Base Free Conversion of Glycerol to Lactic Acid and Glyceric Acid in Water Using Bimetallic Au–Pt Nanoparticles on Acidic Zeolites

The base free oxidation of glycerol with molecular oxygen in water using bimetallic Au–Pt catalysts on three different acidic zeolite supports (H-mordenite, H-β and H-USY) was explored in a batch setup. At temperatures between 140 and 180 °C, lactic acid formation was significant and highest selectivity (60 % lactic acid at 80 % glycerol conversion) was obtained using Au–Pt/USY-600 (180 °C). A selectivity switch to glyceric acid (GLYA) was observed when the reactions were performed at 100 °C. Highest conversion and selectivity towards GLYA were obtained with Au–Pt/H-β as the catalyst (68 % selectivity at 68 % conversion).

     

Exploratory Catalyst Screening Studies on the Base Free Conversion of Glycerol to Lactic Acid and Glyceric Acid in Water Using Bimetallic Au–Pt Nanoparticles on Acidic Zeolites

The base free oxidation of glycerol with molecular oxygen in water using bimetallic Au–Pt catalysts on three different acidic zeolite supports (H-mordenite, H-β and H-USY) was explored in a batch setup. At temperatures between 140 and 180 °C, lactic acid formation was significant and highest selectivity (60 % lactic acid at 80 % glycerol conversion) was obtained using Au–Pt/USY-600 (180 °C). A selectivity switch to glyceric acid (GLYA) was observed when the reactions were performed at 100 °C. Highest conversion and selectivity towards GLYA were obtained with Au–Pt/H-β as the catalyst (68 % selectivity at 68 % conversion).     

n-heptane hydroconversion over aluminosilicate mesoporous molecular sieves

Aluminosilicate mesoporous molecular sieves (designated Al-MMS) have been prepared at room temperature using the primary amine hexadecylamine as organic templating surfactant. The materials have textural properties typical of mesoporous materials with short-range hexagonal order but exhibit higher Brønsted acidity compared to aluminium-containing MCM-41. The Pt-impregnated materials are efficient catalysts for the hydroconversion of n-heptane. At low Si/Al ratio (≤ 10) the materials have total conversions and selectivity comparable to that of USY zeolite (Si/Al = 21) and in addition exhibit considerable cyclisation at temperatures above 350°C. Our catalytic results show that the Pt-impregnated Al-MMS samples attain a good balance between the metal and acidic functions and that activity and selectivity are dependent on the Brønsted acid content and consequently on the amount of tetrahedral aluminium in the catalysts. The amount of Pt (in the range 0.25-1 wt%) mainly affects the selectivity to cyclised products which increases with Pt content at the expense of cracking; total conversion and selectivity to isomers remain largely unaffected.     

The selectivity changes in 1-hexene isomerization and its relation to acid properties of Pd/SAPO-11, SAPO-11, HZSM-5, and H-mordenite catalysts

The activity and selectivity patterns for 1-hexene isomerrzation have been compared in the temperature range of 150–450°C for four different kinds of acidic zeolites (H-mordenite, HZSM-5, SAPO-11 and Pd/SAPO-11) differing both ir acid properties and geometric structure. At lower reaction temperatures (150–175°C) the predominant reaction pathway was double bond shift(DBS) and was not influenced by the type of catalyst. At higher temperatures significant shifts in selectivity were observed from DBS to cracking (C) or skeletal rearrangement (SR) depending on the type of catalyst. Temperature programmed desorption (TPD) patterns of chemisorbed NH₃ were also determined. Three different peaks were found for the most of TPD patterns. The first peak might be associated with Lewis acidsite, and the other two peaks at higher temperatures might be associated with Brönsted acid-sites. It was found that significant loss of strong Brönsted acidity upon Pd loading on SAPO-11. A selectivity correlation at 350°C showed strong dependence of DBS and cracking on total acidity. The reaction seems well suited for investigation of the interrelation between pore structure and surface acidity in terms of these selectivity factors.     

Producing triacetylglycerol with glycerol by two steps: Esterification and acetylation

A two-step method is proposed to obtain high selectivity and high conversion rate for producing additive triacetylglycerol of biofuel from its byproduct glycerol. The esterification of glycerol with acetic acid was carried out over resin and zeolites. Amberlyst-35 was found to be an excellent catalyst. The reaction conditions were optimized by testing catalysts, temperatures, feedstock ratios as well as loads of catalysts. The optimal conditions are temperature of 105 °C and an acetic acid to glycerol molar ratio of 9:1 with 0.5 g catalyst. After the 4 hour reaction of the optimal condition, the selectivity of triacetylglycerol reaches almost 100% in 15 min by adding thereto acid anhydride. Recycling experiments indicate that no significant deactivation of Amerlyst-35 occurred during the reaction.     

The liquid-phase dehydration of tert.-butyl alcohol on B-P-O catalysts

The dehydration of tert.-butyl alcohol in the liquid phase has been investigated on BPO catalysts with phosphorus/boron molar ratios from 0.8 to 1.4 and pretreatment temperatures up to 400 °C. A maximum in the initial reaction rate occurs at a P/B of 1.25 and a pretreatment temperature of 100 °C. The reaction is catalyzed by Brønsted acid sites and not Lewis acid centers and appears to proceed through a carbonium ion mechanism.     

Lewis and Brønsted acid catalysis with AlMCM-41 and AlMMS: dependence on exchange cation

Mesoporous solid acid catalysts based on AlMCM-41 and AlMMS have been prepared. The two catalysts exhibit similar unidimensional pore structures with hexagonal symmetries. AlMMS shows less long-range order than AlMCM-41 but is considerably easier to synthesise. The catalytic activities have been measured and compared in the Lewis-acid-catalysed alkylation of toluene with benzyl chloride, and the Brønsted-acid-catalysed alkylation of toluene with benzyl alcohol. Activities have been measured for catalysts ion-exchanged with H⁺, Fe³⁺, Al³⁺ and Na⁺, and following thermal activation at temperatures of 150–350°C. They have also been compared with K10, a mesoporous acid-treated clay catalyst. Results show that the acid-treated clay is the most active of the three catalysts in both reactions. For all catalysts, the Fe³⁺ forms exhibit the highest Lewis acid catalytic activities, and the Al³⁺ and H⁺ forms show higher Brønsted acid activities. Infrared spectra of adsorbed pyridine show relative concentrations of Lewis and Brønsted acid sites consistent with this. Differences in the dependence of catalytic activities on thermal activation temperature are interpreted in terms of the hydration properties of the catalysts.     

Zirconia-supported niobia catalyzed formation of propanol from 1,2-propanediol via dehydration and consecutive hydrogen transfer

Vapor-phase catalytic dehydration of 1,2-propanediol was investigated over Zirconia-supported niobia catalysts. The catalysts exhibit selectivity favoring propanol (approximately 39%) at 85.0% 1,2-propanediol conversion at 290 °C under 1 atm N₂. The ZrNbO catalysts were analyzed by various techniques; the results indicated that the active sites were weak Brønsted acid sites. A dehydration and hydrogen transfer mechanism was also proposed.     

Catalytic activity of ZIF-8 in the synthesis of styrene carbonate from CO2 and styrene oxide

The catalytic activity of ZIF-8 in the synthesis of styrene carbonate from carbon dioxide and styrene oxide is presented. ZIF-8 crystals displayed catalytic activity even at temperatures as low as 50 °C, with styrene carbonate yields as high as ~ 54% at 100 °C. In contrast to many prior-art catalysts, solvents or co-catalysts were not required. Pyridine and ammonia were used as probe molecules to estimate the type and density of acid sites in fresh and reused ZIF-8 catalysts. DRIFT spectroscopy of adsorbed pyridine revealed the presence of both Brönsted (B) and Lewis (L) acid sites. The B-sites have nearly vanished in the case of recycled ZIF-8 catalysts. The simultaneous presence of both the acid sites and the nitrogen basic moieties from the imidazole linker in ZIF-8 promoted the adsorption of the CO₂ on the solid surface and its further conversion to the cyclic carbonate. The ZIF-8 catalysts could be recycled and reused without significant loss in catalytic activity.     

Direct synthesis,characterization and catalytic performance of Al–Fe-SBA-15 materials in selective catalytic reduction of NO with NH3

A series of Al–Fe-SBA-15 catalysts were synthesized by microwave methods with various iron and aluminum contents. The samples were characterized by XRD, SEM, TEM, BET, NH₃-TPD, FT-IR. Results indicated that all the samples that exhibited well-ordered hexagonal arrays of mesopores, disk-like and petal-like morphologies were observed for different catalysts. NH₃-TPD indicated that the introduction of Al results in the generation of Brönsted acid originated from Al–OH. Brönsted acid played important roles in the selective catalytic reduction of NO by NH₃, NO_x conversion over Al–Fe-SBA-15 samples increased rapidly as temperature increased and achieved 95% at about 360 °C.     

Effects of water density on acid-catalytic properties of TiO2 and WO3/TiO2 in supercritical water

The effects of water density on the acid-catalytic properties of TiO₂ and WO₃/TiO₂ catalysts in supercritical water at 400 °C were investigated by using the kinetic analysis of the dehydration reaction of glycerol. The reaction selectivity of TiO₂ and WO₃/TiO₂ catalysts and the apparent-reaction orders for water indicated that the acid-catalytic properties of these two catalysts show different dependence on water density. In the reaction using TiO₂, the contribution of Lewis acid sites in TiO₂ was large at a low water density, while the contribution of Brönsted acid sites in TiO₂ increased with increasing water density. On the other hand, the reaction using WO₃/TiO₂ was mainly catalyzed by Brönsted acid sites in WO₃/TiO₂ even at a low water density, and the nature of Lewis/Brönsted acid sites in WO₃/TiO₂ was not influenced by the water density.     

Generation of Brønsted Acid Over Alumina-Supported Niobia Calcined at High Temperatures

Nb₂O₅/Al₂O₃ catalysts calcined at high temperatures exhibited the Brønsted acid property. A monolayer of niobic acid-like compound, which has distorted octahedral symmetry, was stabilized over 16 wt% Nb₂O₅/Al₂O₃ catalyst calcined at 1,173 K. The two-dimensional Nb–O–Nb network of stabilized niobic acid-like compound probably accounts for the generation of Brønsted acid.     

Sorbitol Hydrogenolysis Over Ni, Pt and Ru Supported on NaY

The hydrogenolysis of sorbitol into 1,2-propanediol (PD), ethylene glycol (EG) and glycerol (G) was investigated over Ni, Pt and Ru supported on NaY at 220 °C and 60 bar in a batch reactor. Ni(6 %)–NaY was investigated in detail at different process conditions, including its recyclability. Attempts have been made to rationalize the experimentally observed conversion and product selectivity obtained over the different catalysts with results of Density Functional Theory calculations of adsorption energy and bond length changes in sorbitol adsorbed over various planes of Ni, Pt and Ru.     

Pt/Ni wet impregnated over Al incorporated mesoporous silicates: a highly efficient catalyst for anisole hydrodeoxygenation

This work reports, formation of benzene from anisole via hydrodeoxygenation process using vapour phase fixed bed reactor. The surface properties of bimetallic catalysts such as textural properties, acidic, and Pt/Ni dispersion has established by various characterization techniques. The reaction was carried out at 370 and 420 °C with space velocity 3.3 & 6.6 h^??1, over acidic and non-acidic supported mono and bimetallic catalysts. The optimum conversion and selectivity was observed at 420 °C and WHSV?=?3.3 h^??1 for all mono and bimetallic catalysts. Pt/Ni/Al-SBA-15 acidic bimetallic catalyst shows maximum anisole conversion 59% with benzene selectivity 37% under atmospheric pressure, due to the more acidic centres and high dispersion of Pt/Ni species on the bimetallic catalyst, enhance the anisole conversion; this was proved by NH₃-TPD and HR-TEM analysis. The acidic Pt/Ni bimetallic catalyst shows higher anisole conversion as compared to the mono metallic Pt/Ni catalysts and it works predominantly through demethylation and hydrogenolysis reaction pathway.     

Gold-Nano Particles Supported on Na-Y and H-Y Types Zeolites: Activity and Thermal Stability for CO Oxidation Reaction

Gold nano particles (GNP) were deposited on Na-Y and H-Y zeolite substrates using chloroauric acid (HAuCl₄) solution. The synthesized catalysts were then characterized and the catalytic activity toward CO oxidation reaction was investigated using a tubular fix bed micro reactor under atmospheric pressure. It was found that CO conversion of 100% and 5% can be achieved at 20 °C on Au/Na-Y and Au/H-Y fresh catalysts, respectively. Thermal stability of catalysts was also investigated by treating the catalysts at 400 °C for 4 h. After thermal stability test, activity tests of the catalysts at 20 °C were shown that CO conversion of Au/Na-Y catalyst was decreased to 65% whereas the activity of the Au/H-Y at 20 °C was increased up to 15%. Characterization tests were revealed that the structures of the zeolitic supports were remained unchanged after thermal pretreatment.     

Steam conversion of glycerol on Ni and Au-Ni catalysts

During primary screening, catalysts which enable production of syngas or hydrogen from glycerol with high yields under soft conditions were revealed. Nickel and nickel-gold catalysts on various supports support were studied in the reaction of steam conversion of glycerol. Nickel catalysts on acidic supports (F-Al₂O₃ and B₂O₃-Al₂O₃) were ascertained to provide 73% selectivity toward H₂ at temperatures as low as 520°C, glycerol conversion amounting to 48%, which allows one to consider these catalysts to be applicable for H₂ production from glycerol. 30% Ni/Al₂O₃ catalyst produced according to the original sol-gel procedure allows one to obtain syngas with a composition suitable for methanol production at relatively low temperatures (520–570°C) and almost complete glycerol conversion. A strongly pronounced synergetic effect was ascertained for 0.27% Au-0.09% Ni/Al₂O₃. Glycerol conversion on this catalyst at 570°C attains 67%; the composition of the resultant gas mixture is applicable for methanol production.     

Etherification of glycerol to polyglycerols over hydrotalcite catalyst prepared using a combustion method

Selective etherification of glycerol to polyglycerols by hydrotalcite catalysts prepared using combustion method was investigated. Characteristics and activity of catalysts synthesized using various fuel types in the combustion method (glucose, fructose and saccharose) and calcination temperature (450 °C to 850 °C) were elucidated. Due to suitable molecular size and enthalpy, glucose was the most suitable fuel to be used. Calcination at 650 °C led to the highest catalytic activity (77.7% conversion) in 16 h. However, 850 °C was detrimental to catalytic activity due to the extraction of MgO from the hydrotalcite framework.