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.     

Efficient synthesis of glycerol carbonate from glycerol and urea with lanthanum oxide as a solid base catalyst

Lanthanum oxide catalyst prepared by precipitation method and calcined at 600 °C exhibited better catalytic activity in the catalytic synthesis of glycerol carbonate from glycerol and urea with TOF up to 1506 mmol/g·h. It was proposed that the lanthanum oxide catalyst with more strong basic sites (T_d > 400 °C) exhibited higher catalytic activity. Accordingly, the catalyst containing appropriate amount of La₂O₂CO₃ phase exhibited higher catalytic activity. Moreover, the recycling experiments demonstrated that the catalytic activity can be essentially preserved during the recycling tests investigated.     

Influence of SBA-15 support on CeO2–ZrO2 catalyst for the dehydrogenation of ethylbenzene to styrene with CO2

Pure oxides of ceria (CeO₂) and zirconia (ZrO₂) were prepared by precipitation method and a catalyst comprising of 25 mol% of CeO₂ and 75 mol% of ZrO₂ (25CZ) mixed metal oxide was prepared by co-precipitation method and also a catalyst with 25 wt% of 25CZ (25 mol% of CeO₂ and 75 mol% of ZrO₂) and 75 wt% SBA-15(25/25CZS) was prepared by precipitation–deposition method. Aqueous NH₃ solution was used as a hydrolyzing agent for all the precipitation reactions. These catalysts were characterized by X-ray diffraction and nitrogen adsorption–desorption techniques for the confirmation of SBA-15 structural intactness. All these catalysts were found to be effective for the oxidative dehydrogenation of ethylbenzene (ODHEB) to styrene in the presence of CO₂ and also it was observed that there was a sequential enhancement in the catalytic activity from individual oxides to mixed oxides followed by supported mixed oxide catalysts. Of the catalysts studied in this work, the supported 25/25CZS catalyst exhibited the superior activity, which was about 10–20 times higher than the activity of bulk single oxides in terms of turn over frequency.     

Heterogeneous transesterification processes by using CaO supported on zinc oxide as basic catalysts

Zinc oxide, obtained by thermal decomposition of zinc oxalate, has been impregnated with different amounts of calcium oxide, and used as solid catalyst for transesterification processes. Catalysts have been characterized by chemical analysis, XRD, XPS, FT-IR, SEM, N₂ adsorption–desorption at 77 K and CO₂-TPD. The catalytic behaviour has been evaluated by choosing two transesterification processes: a simple model such as the reaction between ethyl butyrate and methanol and the production of biodiesel from sunflower oil and methanol. Calcium oxide is stabilized by filling the mesoporous network of ZnO, as reveal the corresponding pore size distributions, thus avoiding the lixiviation of the active phase in the reaction medium. These supported CaO catalysts, thermally activated at 1073 K, can give rise to FAME (fatty acid methyl esters) yield higher than 90%, after 2 h of reaction, when a methanol:oil molar ratio of 12 and 1.3 wt% of the catalyst with a 16 wt% CaO were employed.     

Coke removal from deactivated Co–Ni steam reforming catalyst using different gasifying agents: An analysis of the gas–solid reaction kinetics

The reactivity of various gases, namely; O₂, air, CO₂, H₂ and N₂, with carbon deposited on alumina-supported Co–Ni catalyst during propane reforming in a fluidized bed reactor at 773–973 K using relatively low feed steam:carbon ratio (0.8–1.5) has been investigated in a thermogravimetric analysis unit. Analysis of the transient solid weight loss revealed that carbon removal mechanism is dependent on the type of gasifying agent. Carbon gasification kinetics using O₂ and air followed the Avrami-Erofeev (A2) model while data for both CO₂ and H₂ were captured by the geometrical (contracting area, R2) model. However, carbon gasification with inert N₂ proceeded at much slower rate (about 10 times lower than air) and was adequately fitted by the one-dimensional diffusion (D1) model. Specific reaction rates from these phenomenological models were also linearly correlated with the catalyst carbon content with reactivity coefficient of the gasifying agent decreasing in the order, O₂ > air > CO₂ > H₂ > N₂. In order to minimize energy consumption during catalyst regeneration, reduce greenhouse gas emissions and reduce catalyst sintering, it would be desirable to employ a mixture of air and CO₂ as the carbon gasifying agent to take advantage of the coupled exothermic (air oxidation) and endothermic (reverse Boudouard reaction involving CO₂ and carbon) nature taking place during the carbon removal operation.     

Catalytic CO2 reforming of methane over Ir/Ce0.9Gd0.1O2−x

CO₂ reforming of methane over Ir loaded Ce_0.9Gd_0.1O_2−x (Ir/CGO) has been studied between 600 and 800 °C and for CH₄/CO₂ ratios between 2 and 0.66 in order to evaluate its potential use as an anode material for direct conversion of biogas at moderate temperatures in solid oxide fuel cells. The catalyst exhibited a superior catalytic activity compared to the support alone and other Ir based catalysts. High CH₄/CO₂ ratios and temperatures were required to obtain the maximum H₂/CO ratio, which could never exceed unity. Long-term experiments were carried out, showing the excellent stability of the catalyst with time on stream. Carbon formation was totally inhibited (in most experimental conditions) or very limited in the most severe conditions of the study (800 °C, CH₄/CO₂ = 2). This carbon was found to be highly reactive towards O₂ upon TPO experiments.     

Solvent free synthesis of chalcone and flavanone over zinc oxide supported metal oxide catalysts

Liquid phase Claisen–Schmidt condensation between 2′-hydroxyacetophenone and benzaldehyde to form 2′-hydroxychalcone, followed by intramolecular cyclisation to form flavanone was carried out over zinc oxide supported metal oxide catalysts under solvent free condition. The reaction was carried out over ZnO supported MgO, BaO, K₂O and Na₂O catalysts with 0.2 g of each catalyst at 140 °C for 3 h. Magnesium oxide impregnated zinc oxide was observed to offer higher conversion of 2′-hydroxyacetophenone than other catalysts. Further MgO impregnated with various other supports such as HZSM-5, Al₂O₃ and SiO₂ were also used for the reaction to assess the suitability of the support. The order of activity of the support is ZnO > SiO₂ > Al₂O₃ > HZSM-5. Various weight percentage of MgO was loaded on ZnO to optimize maximum efficiency of the catalyst system. The impregnation of MgO (wt%) in ZnO was optimized for better conversion of 2′-hydroxyacetophenone. The effect of temperature and catalyst loading was studied for the reaction.     

Water-tolerant graphene oxide as a high-efficiency catalyst for the synthesis of propylene carbonate from propylene oxide and carbon dioxide

Graphene oxide (GO) was found to be a metal-free, water-tolerant and high-efficiency catalyst towards the cycloaddition of carbon dioxide (CO₂) to propylene oxide (PO) for the synthesis of propylene carbonate (PC) at room temperature (RT) and atmospheric pressure without the need for a solvent. Using GO as catalyst and tetrabutylammonium bromide (Bu₄NBr) as co-catalyst, PO is rapidly converted to PC with 96% yield and 100% selectivity under relatively mild conditions (100 °C, 2.25 MPa, 1 h). The effects of catalyst amount, temperature, time and water (H₂O) addition on the reaction were investigated. It is found that the presence of a proper amount of H₂O enhances the conversion of epoxide remarkably. A comparison of the catalytic activities of a number of reduced graphene oxide (r-GO) samples under similar reaction conditions revealed that it is the hydroxyl groups (rather than the carboxyl groups) on GO that form hydrogen bonds with PO, and act synergistically with halide anions to promote the cycloaddition reaction. A possible mechanism is proposed.     

Selective epoxidation of styrene with air catalyzed by CoOx and CoOx/SiO2 without any reductant

Cobalt oxide (CoOx) prepared by a direct calcination of cobalt nitrate was considerably active for the epoxidation of styrene with air in DMF under mild conditions. A substrate conversion of 75.8 mol% with an epoxide selectivity of 82.1% was achieved at 353 K over 10 mg of cobalt oxide catalyst. Once CoOx was loaded on the support SiO₂ through a simple procedure consisting of wet impregnation, drying and calcination, the as-prepared catalyst presented higher catalytic activity and epoxide selectivity than cobalt oxide itself. Over the optimized catalyst CoOx/SiO₂ (1.0 wt% Co), 85.7 mol% of styrene was effectively converted at 363 K within 4 h, with a high epoxide selectivity up to 86.0%. The results showed that many factors influenced the performance of the catalyst, such as the Co loading, the support, the temperature and the atmosphere, etc. The leaching of cobalt from the catalyst CoOx/SiO₂ was negligible, indicating the applicability of the catalyst CoOx/SiO₂ as a true heterogeneous catalyst. The control test and UV–vis spectra revealed a synergic interaction among solvent, oxygen and substrate over CoOx/SiO₂.     

One-pot synthesized multi-functional graphene oxide as a water-tolerant and efficient metal-free heterogeneous catalyst for cycloaddition reaction

A series of functional graphene oxide (F-GO) materials were prepared by silylanization of graphene oxide (GO) with chlorine-terminal silanes and subsequent nucleophilic substitution reaction with tertiary amine in a one-pot approach. The quaternary ammonium salt was generated and immobilized simultaneously in situ, and the primary amine is beneficial to improve the number of surface functionalities on GO. This is the first time that a multi-functional GO material was designed, prepared and used for the synthesis of cyclic carbonates through the cycloaddition of carbon dioxide (CO₂) to epoxides. The F-GO catalyst can be easily separated and reused for at least five times without significant loss of activity (TOF = 46.4 h⁻¹). The excellent performance is attributed to the synergetic effect of silanol group and halide anion for ring opening of epoxide as well as the role of amine for CO₂ adsorption and activation. A possible mechanism is proposed for the cycloaddition reaction over F-GO.     

Low-temperature catalytic conversion of lignite: 1. Steam gasification using potassium carbonate supported on perovskite oxide

The catalytic conversion of alkali metal carbonate (K₂CO₃) catalyst supported on perovskite oxide was carefully examined as an effective catalyst for low-temperature catalytic gasification of lignite. It showed much higher activity than K₂CO₃ alone as well as K₂CO₃ supported on γ-alumina under gasification conditions below 800 °C. Furthermore, catalyzed syngas had higher H₂ and lower CO₂ ratios than non-catalyzed syngas. Promisingly, there was also much less tar formation, less than 50 wt.% compared to non-catalyzed gasification. Also, less loss of K₂CO₃ and no coke formation on the catalyst surface were confirmed, comparing to the catalytic gasification with K₂CO₃ supported on γ-alumina.     

Characterisation of BN-supported palladium oxide catalyst used for hydrocarbon oxidation

Hexagonal boron nitride (BN), with a graphite-type structure and with surface area of 184 m²/g was used as a support for palladium oxide (PdO/BN). About 1 wt% of palladium was deposited on BN by incipient wetness method by using palladium nitrate as precursor. The support and the catalyst were characterized by BET, TEM, XRD, XPS, ICP, TG, TPD, in situ ac electrical conductivity and by ammonia adsorption microcalorimetry. Oxidation of propylene and methane were used as model reactions to study the catalytic properties of the PdO/BN catalyst. The BN support was practically inactive in propylene oxidation up to 400 °C, while the onset of the oxidation was detected around 200 °C on PdO/BN, which points out the role of the palladium in adsorption of the reactive hydrocarbon species. At the same time, this temperature is coincident with the increase of the electronic conductivity on both BN and PdO/BN samples, which is important for oxygen adsorption/activation as electrophilic species. The catalyst was inactive in methane oxidation below 400 °C. Only about 2% CH₄ conversion was observed at 400 °C, increasing sharply up to 87% at 550 °C with methane transformation only to CO₂ and water.     

High pressure plant for heterogeneous catalytic CO2 hydrogenation reactions in a continuous flow microreactor

The CO₂ hydrogenation to methanol is favored by high pressure from the thermodynamic point of view. Mostly experimental work on this reaction is limited at 400 bar due to technical and safety reasons. In this work we present a high pressure plant able to conduct CO₂ hydrogenation reactions at pressures up to 950 bar in a capillary microreactor; we focus on the influence of pressure concerning process intensification.To validate the plant functionality the reverse water–gas shift (RWGS) reaction was conducted over a 1 wt% Pt/CeO₂ catalyst at 450 °C and between 200 and 950 bar. A mass flow controller for hydrogen was developed due to lack of commercial available hydrogen mass flow controller able to work in the micro liter per minute range and up to 1000 bar. Additional to the RWGS reaction two more reactions take place. The first is the CO disproportionation reaction which results in deposited carbon on the catalyst. The second is the subsequent hydrogenation of carbon to methane. The experimentally determined CO₂ conversion is clearly below the equilibrium of the entire reaction network, hence the reaction is kinetically limited. The reaction performance increases with pressure showing process intensification.     

Density and N2O solubility of sodium and potassium carbonate solutions in the temperature range 25 to 80 °C

To deduce kinetic parameters for the reactions of carbon dioxide (CO₂) in carbonate solutions the physical solubility of CO₂ into the reacting solution is needed. To measure the physical solubility directly with CO₂ is not possible, so the solubility of nitrous oxide (N₂O) is normally measured instead. The physical solubility of CO₂ can then be calculated based on the solubility of CO₂ and N₂O into water and the solubility of N₂O in the solution of interest invoking the so called N₂O analogy (Clarke, 1964; Laddha et al., 1981). To obtain good accuracy of the solubility measurements the accurate density of the solution is needed. In this study the densities were measured with pycnometers up to 353 K.In this paper the parameters in the model of Weisenberger and Schumpe (1996) were refitted specifically for the two carbonate systems using experimental data up to 353 K and up to 30 wt% (3.7 kmol/m³) aqueous sodium carbonate and up to 50 wt% (5.5 kmol/m³) aqueous potassium carbonate solutions.     

Hydrogenation of phenol in scCO2 over carbon nanofiber supported Rh catalyst

A catalyst of Rh nanoparticles supported on a carbon nanofiber, 5 wt.% Rh/CNF, with an average size of 2–3 nm has been prepared by a method of incipient wetness impregnation. The catalyst presented a high activity in the ring hydrogenation of phenol in a medium of supercritical CO₂ (scCO₂) at a low temperature of 323 K. The presence of compressed CO₂ retards hydrogenation of cyclohexanone to cyclohexanol under the reaction conditions used, and this is beneficial for the formation of cyclohexanone, increasing the selectivity to cyclohexanone. But the selectivity to cyclohexanone is very low at the completion of reaction in the absence of CO₂, at low CO₂ pressures, and in the presence of pressurized N₂ instead of CO₂. That is, high selectivity to cyclohexanone can be achieved with CO₂ species at higher pressures but not with the application of an inert hydrostatic pressure on the liquid substrate phase.     

Mechanism of NO reduction by CO over Pt/SBA-15

The mechanism of the CO + NO reaction catalyzed by Pt/SBA-15 was studied via independent investigations of CO oxidation and NO disproportionation. Below 400 °C, both CO + O₂ and CO + NO reactions approach 100 % conversion, while the catalyst shows negligible activity for NO disproportionation. These results suggest that CO oxidation by atomic oxygen arising from NO dissociation is not a major route for CO₂ formation in the CO + NO reaction. In situ IR spectra reveal the formation of isocyanates (NCO⁻) adsorbed on silica. Their surface concentration changes with the extent of the CO + NO reaction. A mechanism is proposed in which isocyanates are reaction intermediates.     

Oxidative dehydrogenation of 1-butene to 1,3-butadiene over BiFe0.65NixMo oxide catalysts: Effect of nickel content

BiFe_0.65Ni_xMo oxide catalysts (x = 0–0.2) were prepared and applied for the oxidative dehydrogenation of butenes to 1,3-butadiene. Temperature programmed reoxidation (TPRO) measurements revealed that the catalytic activity was closely related to the oxygen mobility. The surface modification by small amounts of nickel addition is favorable in this reaction. Among the catalysts studied here, BiFe_0.65Ni_0.05Mo oxide catalyst showed the highest conversion and BD yield (X = 86% and Y_BD = 72%) due to the high oxygen mobility. The BiFe_0.65Ni_0.05Mo oxide catalyst is very stable and no deactivation during the 100 h reaction was shown.     

Polyoxometalate as co-catalyst of tetrabutylammonium bromide in polyethylene glycol (PEG) for coupling reaction of CO2 and propylene oxide or ethylene oxide

The coupling reaction of CO₂ and propylene oxide or ethylene oxide to produce corresponding cyclic carbonate in the presence of a catalytic system composed of n-Bu₄NBr, α₂-(n-Bu₄N)₉P₂W₁₇O₆₁(Co²⁺ · Br) (abbreviated as P₂W₁₇Co) and PEG (MW 400) has been investigated. The experimental results indicated that the synthesis of propylene carbonate (PC) or ethylene carbonate (EC) achieved with over 98% yield and 100% selectivity within 1 h at 120 °C by using the above catalyst system. When the catalyst system was recycled, the catalytic activity slowly diminished. Moreover, a plausible mechanism was proposed.     

A novel low-temperature methanol synthesis method from CO/H2/CO2 based on the synergistic effect between solid catalyst and homogeneous catalyst

The activity of a binary catalyst in alcoholic solvents for methanol synthesis from CO/H₂/CO₂ at low temperature was investigated in a concurrent synthesis course. Experiment results showed that the combination of homogeneous potassium formate catalyst and solid copper–magnesia catalyst enhanced the conversion of CO₂-containing syngas to methanol at temperature of 423–443 K and pressure of 3–5 MPa. Under a contact time of 100 g h/mol, the maximum conversion of total carbon approached the reaction equilibrium and the selectivity of methanol was 99%. A reaction pathway involving esterification and hydrogenolysis of esters was postulated based on the integrative and separate activity tests, along with the structural characterization of the catalysts. Both potassium formate for the esterification as well as Cu/MgO for the hydrogenolysis were found to be crucial to this homogeneous and heterogeneous synergistically catalytic system. CO and H₂ were involved in the recycling of potassium formate.     

In situ FTIR micro-spectroscopy to investigate polymeric fibers under supercritical carbon dioxide: CO2 sorption and swelling measurements

An original experimental set-up combining a FTIR (Fourier Transformed InfraRed) microscope with a high pressure cell has been built in order to analyze in situ and simultaneously the CO₂ sorption and the polymer swelling of microscopic polymer samples, such as fibers, subjected to supercritical carbon dioxide. Thanks to this experimental set-up, we have determined as a function of the CO₂ pressure (from 2 to 15 MPa) the CO₂ sorption and the polymer swelling at T = 40 °C of four polymer samples, namely PEO (polyethylene oxide), PLLA (poly-l-lactide acid), PET (polyethylene terephtalate) and PP (polypropylene). The quantity of CO₂ sorbed in all the studied polymers increases with pressure. PEO and PLLA display a significant level of CO₂ sorption (20 and 25% respectively, at P = 15 MPa). However, we observe that a lower quantity of CO₂ can be sorbed into PP and PET (7 and 8% respectively, at P = 15 MPa). Comparing their thermodynamic behaviors and their intrinsic properties, we emphasize that a high CO₂ sorption can be reach if on one hand, the polymer is able to form specific interaction with CO₂ in order to thermodynamically favor the presence of CO₂ molecules inside the polymer and on the other, displays high chains mobility in the amorphous region. PLLA and PEO fulfilled these two requirements whereas only one property is fulfilled by PET (specific interaction with CO₂) and PP (high chains mobility). Finally, we have found that for a given CO₂ sorption, the resulting swelling of the polymer depends mainly on its crystallinity.