Tungstophosphoric acid supported on titania: A solid acid catalyst in benzylation of phenol with benzylalcohol

Benzylation of phenol with benzylalcohol was carried out in liquid phase over tungstophosphoric acid (TPA) supported on titania. The catalysts were prepared with different TPA (10–25%) loading by wet impregnation method, were calcined at 700 °C and characterized by XRD, surface area, FTIR and acidity of the catalysts was measured by temperature programmed desorption of NH₃–TPD, FTIR pyridine adsorption. The catalysts have been represented by a general formula as xPTiO₂₋y (where x = wt%, P = TPA, and y = calcination temperature in °C). The 20PTiO₂ catalyst calcined at various temperatures to know the effect of calcination temperature on activity of the catalyst and the 20PTiO₂-700 showed highest activity in benzylation of phenol with benzylalcohol because it had highest acidity. The effects of temperature, catalyst weight, mole ratio of the reactants on conversion of phenol and product selectivities have been optimized. 20PTiO₂-700 catalyst gave conversion of benzylalcohol (BA) 98% and the selectivity to benzyl phenol (BP) 83.6%, phenyl benzyl ether (PBE) 9.4%, benzylether (BE) 7% at 130 °C, phenol to benzylalcohol molar ratio 2 and in 1 h.     

n-Butyl acrylate production by esterification of acrylic acid with n-butanol combined with pervaporation

In this study, the esterification reaction of acrylic acid and n-butanol to produce n-butyl acrylate and water was studied using the pervaporation–esterification hybrid process to perform the separation and reaction simultaneously to increase the conversion of limiting reactant. A Pervap 2201 polymeric membrane was used to separate water and also to shift the equilibrium. The Pervap 2201 membrane showed high selectivity to water in the n-butanol, acrylic acid, n-butyl acrylate, and water reaction system. The effects of temperature, the initial molar ratio of n-butanol to acrylic acid, catalyst loading, and the ratio of membrane area to reaction volume (S/V) were studied. The maximum conversion of acrylic acid was calculated as 96.3% at a temperature of 358 K, a molar ratio of 8, with a catalyst loading of 10 g/L and an S/V ratio of 70 m⁻¹.     

Meerwein–Ponndorf–Verley reaction of acetophenones with 2-propanol over MgAl mixed oxide: The substituent effect

The MPV reaction of several substituted acetophenones with 2-propanol over an Mg(Al)O_x catalyst were carried out to estimate the Hammett’s reaction constant. Also, the MPV reaction of acetophenone was carried out at different temperatures and variable amount of catalyst and 2-propanol:acetophenone molar ratios. The results show that the optimal reaction conditions are: 82 °C, 1 g of catalyst and an alcohol:ketone molar ratio of 30. In these conditions the yield and selectivity to 1-phenylethanol are 90% and 100%, respectively. These results are similar or better than the obtained by other catalysts in this process.     

Ionic liquid as an efficient promoting medium for synthesis of dimethyl carbonate by oxidative carbonylation of methanol

The synthesis of dimethyl carbonate by oxidative carbonylation of methanol using Cu salt catalysts in the presence of various room temperature ionic liquids (RTILs) was reported. Among the ionic liquids used, N-butylpyridinium tetrafluoroborate was the most effective promoter in terms of the conversion of methanol and the selectivity to dimethyl carbonate (DMC). The influences of reaction temperature, pressure, time, molar ratio of CO/O₂, and amount of the ionic liquid on the oxidative carbonylation of methanol were investigated. The results indicated that under the reaction conditions of 120 °C and 2.4 MPa of a 2:1 mixture of CO and O₂, 17.2% conversion of methanol, 97.8% selectivity of DMC and a DMC productivity of 4.6 g g⁻¹ cat h⁻¹ were achieved. The N-butylpyridinium tetrafluoroborate-meditated CuCl catalyst system could be reused at least five recycles with the same selectivity and a slight loss of catalytic activity due to loss of the catalyst during handling and transferring the reaction mixture.     

Biodiesel production from waste cooking oil in a microtube reactor

Waste cooking oil (WCO) was used to produce biodiesel in a microtube reactor. First, the acid value of the WCO was reduced from 3.96 mg KOH/g to less than 1 mg KOH/g via acid catalyzed esterification. The effects of the methanol-to-WCO molar ratio (4.5:1–18:1), the H₂SO₄ concentration (0.5–2 wt.%), reaction temperature (55–70 °C), and reaction time (5–20 s) were studied. The optimal conditions were 9:1 methanol-to-WCO molar ratio, 1 wt.% H₂SO₄, 65 °C and 5 s of reaction time. Triglycerides in the product from the first step were transesterified with methanol and alkaline catalyst. Methyl ester content of the biodiesel was 91.76%.     

Polyoxometalate as effective catalyst for the deep desulfurization of diesel oil

Aiming at the deep desulfurization of the diesel oil, a comparison of the catalytic effects of several Keggin type POMs, including H₃PW_xMo_12?xO₄₀ (x = 1, 3, 6), Cs_2.5H_0.5PW₁₂O₄₀, and H₃PW₁₂O₄₀, was made, using the solution of DBT in normal octane as simulated diesel oil, H₂O₂ as oxidant, and acetonitrile as extractant. H₃PW₆Mo₆O₄₀ was found to be the best catalyst, with a desulfurization efficiency of 99.79% or higher. Hence, it is promising for the deep desulfurization of actual ODS process. The role of the main factors affecting the process including temperature, O/S molar ratio, initial sulfur concentration, and catalyst dosage, was investigated, whereby the favourable operating conditions were recommended as T = 60 °C, O/S = 15, and a catalyst dosage of 6.93 g (H₃PW₆Mo₆O₄₀)/L (simulated diesel). With the aid of GC–MS analysis, sulfone species was confirmed to be the only product after reaction for 150 min. Furthermore, macro-kinetics of the process catalyzed by H₃PW₆Mo₆O₄₀ was studied, from which the reaction orders were found to be 1.02 to DBT and 0.38 to H₂O₂, and the activation energy of the reaction was found to be 43.3 kJ/mol. Moreover, the catalyst recovered demonstrated almost the same activity as the fresh.     

Removal characteristics of nitrogen oxide of high temperature catalytic filters for simultaneous removal of fine particulate and NOx

The CuMnOx catalysts were deep coated into polysulfonamide felts by vacuum suction to simultaneously remove the particulate and nitrogen oxides. This filter consists of a high temperature foam layer as a surface layer, a catalytic pleated felt as a medium layer and glassfiber fabric layer with high temperature phenol resin as a final layer. In this study, the effects of catalyst loading on the pleated felt, operating temperature on nitrogen oxides reduction with NH₃ were mainly investigated. Tests were conducted at operating temperature range from 150 to 250 °C and at face velocity of 1 m/min. Within these ranges, NO removal efficiency was over 90% at the catalyst loading of 350 g/m² and 200 °C.     

Ceramic monolith supported Mn–Ce–M ternary mixed-oxide (M=Cu,Ni or Co) catalyst for VOCs catalytic oxidation

The MO_x (M=Cu, Ni or Co) modified manganese-cerium mixed-oxide catalysts supported on ceramic monolith were prepared by sol-gel method and examined for the catalytic combustion of o-xylene. Results show that the addition of CuO_x could significantly enhance the catalytic properties of the monolithic catalysts, which may be correlated with the Mn-Cu synergistic interaction. The effects of the preparation parameters including the Cu content, the total amount of active phase and the calcination temperature and time, as well as the reaction conditions, i.e., the space velocity and concentration of o-xylene, on the catalytic performance for the combustion of o-xylene were also investigated. It is shown that the MnCeCu_0.4/monolith catalyst with the active phase loading of 11.4 wt% and calcined at 500 °C for 3 h displays the highest catalytic activity. When the concentration of o-xylene is 1000 ppm and the space velocity is 10,000 h⁻¹, the temperature at which 90% o-xylene conversion is reached is 277 °C. It is also seen that the optimum catalyst has a good catalytic stability and exhibits an excellent activity not only at a rather high space velocity but also within a wide range of o-xylene concentration. Furthermore, the optimum catalyst also show the high combustion performance for other hydrocarbons, e.g., n-butanol and styrene.     

Mn/Mg/Al-spinels as catalysts for SOx abatement: Influence of CeO2 incorporation and catalytic stability

Mg,Mn,Al-oxides with spinel structure, Al/(M²⁺ + Al) molar ratio of 0.25 and 0.50 and an Mn/Mg molar ratio of 0.30 have been evaluated as catalysts for SO_x removal under conditions similar to those found in FCC units. The best performance was that of the sample with the higher aluminium content. The incorporation of CeO₂ in this sample favored SO_x uptake for short reaction times as well as the reduction of the sulfated catalysts. When the regeneration was started at 530 °C, only H₂S was observed as reaction product, but when this step started at 650 °C, the release of SO₂ preceded that of H₂S, regardless of the chemical composition of the sample. As to the additive performance for successive reaction–regeneration cycles, the incorporation of CeO₂ produced a less efficient catalyst with regard to the removal of the SO₂ along the process, but with a higher regeneration efficiency and a lower formation of SO₂ as regeneration product.     

Redox features in the catalytic mechanism of the “standard” and “fast” NH3-SCR of NOx over a V-based catalyst investigated by dynamic methods

The redox mechanism governing the selective catalytic reduction (SCR) of NO/NO₂ by ammonia at low temperature was investigated by transient reactive experiments over a commercial V₂O₅/WO₃/TiO₂ catalyst for diesel exhaust aftertreatment. NO + NH₃ temperature-programmed reaction runs over reduced catalyst samples pretreated with various oxidizing species showed that both NO₂ and HNO₃ were able to reoxidize the V catalyst at much lower temperature than gaseous O₂: furthermore, they significantly enhanced the NO + NH₃ reactivity below 250 °C via the buildup of adsorbed nitrates, which act as a surface pool of oxidizing agents but are decomposed above that temperature. Both such features, which were not observed in comparative experiments over a V-free WO₃/TiO₂ catalyst, point out a key catalytic role of the vanadium redox properties and can explain the greater deNO_x efficiency of the “fast” SCR (NO + NH₃ + NO₂) compared with the “standard” SCR (NO + NH₃ + O₂) reaction. A unifying redox approach is proposed to interpret the overall NO/NO₂–NH₃ SCR chemistry over V-based catalysts, in which vanadium sites are reduced by the reaction between NO and NH₃ and are reoxidized either by oxygen (standard SCR) or by nitrates (fast SCR), with the latter formed via NO₂ disproportion over other nonreducible oxide catalyst components.     

Impact of support oxide and Ba loading on the NOx storage properties of Pt/Ba/support catalysts: CO2 and H2O effects

A series of 1 wt.%Pt/_xBa/Support (Support = Al₂O₃, SiO₂, Al₂O₃-5.5 wt.%SiO₂ and Ce_0.7Zr_0.3O₂, x = 5–30 wt.% BaO) catalysts was investigated regarding the influence of the support oxide on Ba properties for the rapid NO_x trapping (100 s). Catalysts were treated at 700 °C under wet oxidizing atmosphere. The nature of the support oxide and the Ba loading influenced the Pt–Ba proximity, the Ba dispersion and then the surface basicity of the catalysts estimated by CO₂-TPD. At high temperature (400 °C) in the absence of CO₂ and H₂O, the NO_x storage capacity increased with the catalyst basicity: Pt/20Ba/Si < Pt/20Ba/Al5.5Si < Pt/10Ba/Al < Pt/5Ba/CeZr < Pt/30Ba/Al5.5Si < Pt/20Ba/Al < Pt/10BaCeZr. Addition of CO₂ decreased catalyst performances. The inhibiting effect of CO₂ on the NO_x uptake increased generally with both the catalyst basicity and the storage temperature. Water negatively affected the NO_x storage capacity, this effect being higher on alumina containing catalysts than on ceria–zirconia samples. When both CO₂ and H₂O were present in the inlet gas, a cumulative effect was observed at low temperatures (200 °C and 300 °C) whereas mainly CO₂ was responsible for the loss of NO_x storage capacity at 400 °C. Finally, under realistic conditions (H₂O and CO₂) the Pt/20Ba/Al5.5Si catalyst showed the best performances for the rapid NO_x uptake in the 200–400 °C temperature range. It resulted mainly from: (i) enhanced dispersions of platinum and barium on the alumina–silica support, (ii) a high Pt–Ba proximity and (iii) a low basicity of the catalyst which limits the CO₂ competition for the storage sites.     

Synthesis and characterization of Ce–La oxides for the formation of dimethyl carbonate by transesterification of propylene carbonate

A series of cerium–lanthanum catalysts prepared using the co-precipitation method were investigated for transesterification of propylene carbonate (PC) with methanol to produce dimethyl carbonate (DMC). Synthesized catalysts were characterized by XRD, CO₂- and NH₃-TPD, N₂ adsorption/desorption and SEM–EDX techniques. Studies were carried out to study the effect of reaction conditions such as methanol/PC molar ratio (4–12), catalyst dose (2–10 wt.% of PC), reaction time (2–10 h) and temperature (140–180 °C) on the DMC yield. Highest PC conversion and DMC yield of 72% and 74%, respectively, were observed with catalysts having a 1:4 Ce/La molar ratio.     

Synthesis of 3,3′-dimethyl-4,4′-diaminodiphenylmethane catalyzed by zeolites replacing mineral acids

Synthesis of 3,3′-dimethyl-4,4′-diaminodiphenylmethane (MDT) from o-tolylamine and formaldehyde over zeolites was investigated. Among the three tested zeolites, Hβ showed higher catalytic activity than HY and HZSM-5 for MDT synthesis. In the case of Hβ as a catalyst, the effects of feed composition, reaction time and temperature on the yield and selectivity of product MDT were further examined to optimize process conditions. In an o-tolylamine:formaldehyde = 8:1 molar ratio, the two-step reaction running at 413 K for 0.5 h and then 433 K for 0.5 h gave the MDT yield of 87.5%.     

Mesoporous CexZr1−xO2 solid solutions supported CuO nanocatalysts for toluene total oxidation

Mesoporous Ce_xZr_1−xO₂ solid solutions were prepared by the surfactant-assisted method and used as support of CuO nanocatalysts for catalytic total oxidation of toluene. The prepared CuO/Ce_xZr_1−xO₂ catalysts have a wormhole-like mesoporous structure with high surface area and uniform pore size distribution, and the CuO nanoparticles were highly dispersed on the surface of Ce_xZr_1−xO₂. The doping of ZrO₂ in CeO₂ promotes the dispersion of active copper species and enhances the reducibility of copper species. The effect of Ce/Zr ratio, calcination temperature and CuO loading amount on the catalytic performance of CuO/Ce_xZr_1−xO₂ was investigated in detail. The 400 °C-calcined 8%CuO/Ce_0.8Zr_0.2O₂ catalyst exhibits the highest activity with the complete toluene conversion temperature of 275 °C at the condition of GHSH = 33,000 h⁻¹ and the toluene concentration of 4400 ppm. The interfacial interaction between CuO and the Ce_xZr_1−xO₂ support, highly dispersed CuO nanoparticles and the nature of the support contribute to the high catalytic activity of mesoporous CuO/Ce_xZr_1−xO₂ nanocatalysts.     

Dielectric properties of cubic bismuth based pyrochlores containing lithium and fluorine

In this work dielectric properties of Bi_1.5Zn_1?xLi_xNb_1.5O_7?xF_x with x = 0.25 were investigated in a 20 Hz–12 GHz frequency and 120–500 K temperature range and compared to that of regular cubic BZN (when x = 0). Measurements showed that both ceramics have dipolar glass type dielectric dispersion with wide relaxation time distributions. Mean relaxation time follows Arrhenius law in the investigated frequency range, although Vogel–Fulcher law was anticipated.     

A new NOx storage-reduction electrochemical catalyst

A new NO_x storage-reduction electrochemical catalyst has been prepared from a polycrystalline Pt film deposited on 8 mol% Y₂O₃-stabilized ZrO₂ (YSZ) solid electrolyte. BaO has been added onto the Pt film by impregnation method. The NO_x storage capacity of Pt-BaO/YSZ system was investigated at 350 °C and 400 °C under lean conditions. Results have shown that the electrochemical catalyst was effective for NO_x storage. When nitric oxides are fully stored, the catalyst potential is high and reaches its maximum. On the other hand, when a part of NO and also NO₂ desorb to the gas phase, the catalyst potential remarkably drops and finally stabilizes when no more NO_x storage occurs but only the reaction of NO oxidation into NO₂. Furthermore, the investigation has clearly demonstrated that the catalyst potential variation versus temperature or chemical composition is an effective indicator for in situ following the NO_x storage-reduction process, i.e. the storage as well as the regeneration phase. The catalyst potential variations during NO_x storage process was explained in terms of oxygen coverage modifications on the Pt.     

Water-gas shift reaction over Cu–Zn,Cu–Fe,and Cu–Zn–Fe composite-oxide catalysts prepared by urea-nitrate combustion

Water-gas shift reaction was investigated over Cu–Zn, Cu–Fe and Cu–Zn–Fe composite-oxide catalysts at atmospheric pressure from 200 to 375 °C in terms of reducing the CO content with maximal H₂ yield. The Cu_0.15ZnFe₂ spinel catalyst expressed a higher CO conversion level and H₂ yield at a lower temperature compared to the Cu_0.15Zn and Cu_0.15Fe catalysts. Adding H₂O to the feed up to 30% (v/v), but not above, increased the CO reduction level, presumably by increasing the hydroxyl species to react with the adsorbed CO. Increasing the W/F ratio to 0.24 g s cm^?3 increased the CO conversion level to 0.76 at 275 °C with the Cu_0.15ZnFe₂ catalyst, and could be further increased to 0.86 at 350 °C by increasing the Cu molar ratio to 0.30 (Cu_0.30ZnFe₂). Nevertheless, increasing the Cu molar content to 0.50 reduced the CO conversion level. No requirement for adding O₂ when using the Cu_0.30ZnFe₂ catalyst at >260 °C was observed. Increasing the CO content in the reactant decreased its conversion level. The performance of the Cu_0.30ZnFe₂ catalyst was stable over a test period in a CO-rich condition. No undesired product was detected, suggesting a higher selectivity for hydrogen production with a low CO content.     

Benzylation of benzene to diphenylmethane using zeolite catalysts

The catalytic liquid phase benzylation of benzene to diphenylmethane (DPM) with benzyl chloride (BC) is investigated over a number of zeolite catalysts at 358 K and under atmospheric pressure. Conventional homogeneous Lewis acid catalyst, AlCl₃, is also included for comparison. Zeolite H-β is found to be more selective but less active compared to HY and H-ZSM-5 zeolites in the benzylation of benzene. The conversion of BC, rate of BC conversion and selectivity to DPM over H-β after 6 h of reaction time are 33.3 wt%, 4.7 × 10⁻³ mmol g⁻¹ h⁻¹ and 89.1 wt%, respectively. For comparison, the conversion of BC, rate of BC conversion and selectivity to DPM over AlCl₃, under identical reaction condition, are found to be 100 wt%, 170 × 10⁻³ mmol g⁻¹ h⁻¹ and 58 wt%, respectively. Higher amounts of consecutive products are obtained over AlCl₃ due to its non shape selectivity. The acidity of the zeolite catalysts is measured by temperature programmed desorption method. The effect of the duration of the run, SiO₂/Al₂O₃ ratio of H-β, catalyst concentration, reaction temperature and benzene to BC molar ratio on the catalyst performance is also investigated in order to optimize the conversion of BC and selectivity for DPM. The conversion of BC using H-β is increased with the increase in the reaction time, catalyst concentration, reaction temperature and molar ratios whereas it decreases with the increase in SiO₂/Al₂O₃ molar ratio of H-β. H-β is recycled two times and a slight decrease in BC conversion is observed after each cycle, which is related to the minor dealumination of the zeolite catalyst by HCl, which is produced during the reaction as by product. The formation of DPM is explained by an electrophilic attack of the benzyl cation (C₆H₅CH₂⁺) on the benzene ring, which is produced by the polarization of BC over acidic sites of the zeolite catalysts.     

Low-temperature continuous wet oxidation of trichloroethylene over CoOx/TiO2 catalysts

TiO₂-supported metal oxides such as CoO_x, CuO_x, NiO_x and FeO_x have been used for catalytic wet oxidation of trichloroethylene (TCE) in a continuous flow type fixed-bed reactor system, and the most promising catalyst for this wet catalysis has been characterized using XPS and XRD techniques. All the supported catalysts gave relatively low conversions for the wet oxidation at 36 °C, except for 5 wt% CoO_x/TiO₂ which exhibited a steady-state conversion of 45% via a transient activity behavior up to 1 h on stream. XPS measurements yielded that a Co 2p_3/2 main peak at 779.8 eV appeared with the 5 wt% CoO_x/TiO₂ catalyst after the continuous wet TCE oxidation at 36 °C for ca. 6 h (spent catalyst) and this binding energy value was equal to that of Co₃O₄ among reference Co compounds used here, while the catalyst calcined at 570 °C (fresh catalyst) possessed a main peak at 781.3 eV, very similar to that for CoTiO_x species such as CoTiO₃ and Co₂TiO₄. Only characteristic reflections for Co₃O₄ were indicated upon XRD measurements even with the fresh catalyst sample. The simplest model, based on these XPS and XRD results, for nanosized Co₃O₄ particles existing with the fresh catalyst could reasonably explain the transient activity behavior observed upon the wet TCE oxidation.     

Structures and temperature-dependent electrical properties in Ba0.8Sr0.2TiO3–BiAlO3 electrostrictive ceramics

Lead-free piezoceramics of (1 ? x)Ba_0.8Sr_0.2TiO₃–xBiAlO₃ [(1 ? x)BST–xBA (0 ≤ x ≤ 0.12)] have been synthesized and the structures and properties have been investigated systemically. X-ray diffraction patterns indicated that the solid solution limit is close to x = 0.04, and a morphotropic phase boundary (MPB) separating tetragonal and pseudocubic phases exists near x = 0.02. The ferroelectricity weakens monotonously with increasing x, accompanied by weakened butterfly shaped bipolar strain–electric field curves. The temperature dependent properties of the composition with x = 0.02 have been typically investigated, showing that with increasing temperature, the ferroelectricity tends to be weakened. Pure electrostrictive effect has been found in the compositions with x = 0.02 and 0.03 close to room temperature temperature. Based on the results, the effects of BA on structures and electric properties were discussed.