The CO methanation over NaY-zeolite supported Ni/Co3O4, Ni/ZrO2, Co3O4/ZrO2 and Ni/Co3O4/ZrO2 catalysts

The CO methanation was studied over zeolite NaY supported Ni, Co₃O₄, ZrO₂ catalysts. The XRD, N₂ physisorption and SEM analysis were used in order to characterize the catalysts. Catalytic activities were carried out under a feed composition of 1% CO, 50% H₂ and 49% He between the 125 °C to 375 °C. Except for the Ni/Co₃O₄/NaY catalyst, all catalysts gave high surface area because of the presence of zeolite NaY. Average pore diameter of the catalysts fell into the mesopore diameter range. The highest CO methanation activity was obtained with Ni/ZrO₂/NaY catalyst at which the CO methanation was started after 175 °C and 100% CO conversion was obtained at 275 °C using the same catalyst.     

Highly dispersed Mn–Ce mixed oxides supported on carbon nanotubes for low-temperature NO reduction with NH3

A series of Mn–Ce mixed-oxide catalysts supported on carbon nanotubes (CNTs) were prepared for the first time and used for the selective catalytic reduction of NO with NH₃. Mn(0.4)-Ce/CNTs catalysts with loading from 0.6% to 1.8% (molar ratio) in our tests showed more than 90% NO conversion at 120–180 °C at a high space velocity of 42,000 h^− 1. Transmission electron microscopy confirmed that the particle size of Mn–Ce mixed oxides supported on CNTs was 2 to 4 nm. BET result indicated Mn–Ce mixed-oxide catalysts obtained enlarged surface area and pore volume which was beneficial to the catalytic activity.     

Catalysis over bimetallic zeolites: Influence of copper on the catalytic behaviour of nickel in sodium and hydrogen Y zeolites

The catalytic activity of a range of bimetallic nickel/copper zeolite catalysts prepared from NaY and NH₄Y as starting materials has been investigated; the reactions chosen were alkylation of toluene with methanol and the hydrogenation of benzene. The samples prepared from NH₄Y did not reduce benzene although they contained metallic nickel; this is attributed to nickel migration and agglomeration. All the catalysts were active in alkylation and there is evidence that a Cu:Ni ratio of 3:2 favours the formation of intrazeolitic clusters and confers increased acidity on the catalysts.     

Selective reduction of NO by NH3 over Fe-zeolite-promoted V2O5-WO3/TiO2-based catalysts: Great suppression of N2O formation and origin of NO removal activity loss

Great depression of the formation N₂O in the selective catalytic reduction of NO by NH₃ (NH₃-SCR) has been studied by combining a V₂O₅-WO₃/TiO₂ (VWT) catalyst with a Fe-exchanged ZSM-5 zeolite (FeZ). At temperatures > 400 °C, N₂O formation was significant over VWT but < 5 ppm over FeZ/VWT catalysts with the FeZ ≥ 8%. Unfortunately, all these FeZ-promoted catalysts disclosed a decrease in deNO_xing performances, due to an enhanced NH₃ oxidation into NO. At temperatures > 350 °C, the chemically-combined VWT-based FeZ systems could facilitate both N₂O reduction with NH₃ and N₂O decomposition, thereby suppressing N₂O emissions in NH₃-SCR reaction.     

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.     

Influence of CeO2 morphology on the catalytic oxidation of ethanol in air

Nano-CeO₂ catalysts of different shapes were synthesized at different hydrothermal crystallization temperatures from an alkaline aqueous solution. X-ray diffraction (XRD), transmission electron microscope (TEM), and H₂ temperature-programmed reduction (H₂-TPR) were used to study the synthesized nano-CeO₂ catalyst samples. The catalytic properties of the prepared nano-CeO₂ catalysts for the catalytic oxidation of ethanol in air were also investigated. TEM analysis showed that CeO₂ nanorod and nanocube catalysts have been synthesized at hydrothermal crystallization temperatures of 373 K and 453 K, respectively. XRD results showed that the synthesized nano-CeO₂ catalysts have similar cubic fluorite structures. H₂-TPR results indicated that CeO₂ nanorod and nanocube catalysts exhibit different reduction behaviors for H₂ and that the nanorod catalyst has better low-temperature reduction performance than the nanocube catalyst. Ethanol catalytic oxidation results indicated that oxidation and condensation products (including acetaldehyde, acetic acid, CO₂, and ethyl acetate) have been produced from the prepared catalysts. The ethyl acetate and acetic acid can be ignited by ethanol at low temperature on the CeO₂(R) catalyst to give low catalytic combustion temperature for ethyl acetate and acetic acid molecules. CeO₂ nanorods gave ethanol oxidation conversion rates above 99.2% at 443 K and CO₂ selectivity exceeding 99.6% at 483 K, while CeO₂ nanocubes gave ethanol oxidation conversion rates of about 95.1% until 508 K and CO₂ selectivity of only 93.86% at 543 K. CeO₂ nanorod is a potential low-cost and effective catalyst for removing trace amounts of ethanol to purify air.     

Size controlled ZSM-5 on the structure and performance of Fe catalyst in the selective catalytic reduction of NOx with NH3

Fe/ZSM-5 catalysts with various morphologies and sizes were prepared and the catalytic properties in NH₃-SCR were also investigated. The different ZSM-5 morphologies and sizes indeed influence the dispersion of Fe species. The Fe/ZSM-5 catalyst, which was cauliflower-like morphology of ZSM-5 support aggregated by small nano-crystal zeolite with crystallite size of about 50 nm, exhibited the best NH₃-SCR activity (T_≥ 90% = 280–650 °C). This specific morphology and size of ZSM-5 support were considered to benefit the distribution of isolated Fe^3 + species, which was proved to be the main active sites in SCR reaction.     

Selective catalytic reduction of NO by ammonia using mesoporous Fe-containing HZSM-5 and HZSM-12 zeolite catalysts: An option for automotive applications

Mesoporous and conventional Fe-containing ZSM-5 and ZSM-12 catalysts (0.5–8 wt% Fe) were prepared using a simple impregnation method and tested in the selective catalytic reduction (SCR) of NO with NH₃. It was found that for both Fe/HZSM-5 and Fe/HZSM-12 catalysts with similar Fe contents, the activity of the mesoporous samples in NO SCR with NH₃ is significantly higher than for conventional samples. Such a difference in the activity is probably related with the better diffusion of reactants and products in the mesopores and better dispersion of the iron particles in the mesoporous zeolite as was confirmed by SEM analysis. Moreover, the maximum activity for the mesoporous zeolites is found at higher Fe concentrations than for the conventional zeolites. This also illustrates that the mesoporous zeolites allow a better dispersion of the metal component than the conventional zeolites. Finally, the influence of different pretreatment conditions on the catalytic activity was studied and interestingly, it was found that it is possible to increase the SCR performance significantly by preactivation of the catalysts in a 1% NH₃/N₂ mixture at 500 °C for 5 h. After preactivation, the activity of mesoporous 6 wt% Fe/HZSM-5 and 6 wt% Fe/HZSM-12 catalyst is comparable with that of traditional 3 wt% V₂O₅/TiO₂ catalyst used as a reference at temperatures below 400 °C and even more active at higher temperatures.     

Effect of Ce addition on Cr/γ-Al2O3 catalysts for methane catalytic combustion

Cerium modified and chromium-based catalysts using nano-γ-Al₂O₃ as the carrier were prepared via incipient wetness impregnation method and investigated for the catalytic combustion of methane (CH₄). The Cr-based catalysts promoted with 3 wt.% Ce displayed the most effective catalytic activity among all catalysts investigated. In addition, Ce significantly improved the catalytic performance of CH₄ combustion by increasing the amount of reaction site [CrO₄]_ads species on the surface of Cr-based catalysts. Introduction of Ce content also restrained the deactivation of catalysts at high calcination temperature. Cr-based catalysts modified with cerium seem to be a promising cheap and low-temperature catalyst for CH₄ combustion.     

SO42−–Mn–Co–Ce supported on TiO2/SiO2 with high sulfur durability for low-temperature SCR of NO with NH3

The catalysts SO₄^2 − Mn–Co–Ce/TiO₂/SiO₂ were investigated for the low-temperature SCR of NO with NH₃ in the presence of SO₂. An excellent SO₂ durability at low temperature was obtained with the catalyst used TiO₂/SiO₂ as support and modified with SO₄^2 −. The catalyst sulfated with 0.1 mol/L H₂SO₄ solution and then calcined at 300 °C exhibited the best NO_x conversion efficiency of 99.5% at 250 °C in the presence of 50 ppm SO₂. The conversion efficiency did not decrease after repeatedly used for 8 times.     

Aqueous-phase hydrogenation of biomass-derived itaconic acid to methyl-γ-butyrolactone over Pd/C catalysts: Effect of pretreatments of active carbon

The effect of active carbon pretreatment on the catalytic performance of Pd/C catalysts in the hydrogenation of itaconic acid was studied. The catalysts were prepared by deposition–precipitation and characterized by XRD, BET, NH₃-TPD, TEM and FT-IR. Due to the modification of the surface functional groups, surface structure and surface acidities of active carbon via pretreatment, the Pd/C catalysts showed varied catalytic performances. High dispersion and uniform particles were conducive to the excellent activity of Pd/C catalyst with support copretreated with HNO₃ and NaClO, which exhibited 89.5% selectivity towards methyl-γ-butyrolactone at 180 °C, 4 MPa H₂ for 20 h.     

Metal organic framework Cu/MIL-53(Ce)-mediated synthesis of highly active and stable CO oxidation catalysts

The highly dispersed CuO@CeO₂ catalysts were produced from Cu/MIL-53(Ce) through encapsulated copper in a matrix of metal organic framework MIL-53(Ce), serving as a catalyst for CO oxidation. Comparison on the catalytic performance between the CuO@CeO₂ and the (CuO or MIL-53(Ce)) catalytic material has been conducted to understand the catalytic behavior of the catalysts. The CuO@CeO₂ catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), N₂ adsorption-desorption, and the hydrogen temperature-programmed reduction (H₂-TPR). The analyses indicated that the unique CuO@CeO₂ spatial confinement in the obtained solids minimize catalyst deactivation, resulting in high active and stable operation. Indeed, the heterogeneous catalytic composite materials CuO@CeO₂ catalyst exhibited excellent activity in CO oxidation test, with 100% conversion at 79–95 °C and the catalytic activity were stable after reaction 300 h.     

Dimethyl ether synthesis via methanol and syngas over rare earth metals modified zeolite Y and dual Cu–Mn–Zn catalysts

A series of zeolite Y modified with La, Ce, Pr, Nd, Sm and Eu were prepared via ion-exchange, and characterized by XRD, FT-IR and NH₃-TPD. It was found that these rare earth metals were encapsulated in the supercage of zeolite Y and resulted in its enhanced acidity. Among them, La-, Ce-, Pr- and Nd-modified zeolite Y exhibited higher activity and stability (than pure HY) for methanol dehydration to dimethyl ether (DME). For DME synthesis directly from CO hydrogenation using the dual Cu–Mn–Zn/modified-Y catalysts, it was found that Cu–Mn–Zn/La–Y and Cu–Mn–Zn/Ce–Y were more active than Cu–Mn–Zn/pure-HY. The conversion of CO on Cu–Mn–Zn/Ce–HY achieved 77.1% in an isothermal fixed bed reactor at 245 °C, 2.0 MPa, H₂/CO = 3/2 and 1500 h⁻¹.     

Fractional-hydrolysis-driven formation of non-uniform dopant concentration catalyst nanoparticles of Ni/CexZr1 − xO2 and its catalysis in methanation of CO2

Ni/ceria–zirconia solid solution (Ni/Ce_xZr_1 − xO₂) with Ce and Ni enriched on the surface of the catalysts are prepared via a simple, low-cost method. The aqueous phase reactions simplify the preparation process, save the cost and lead the Ce to enriching on the surface of products. The impregnation method makes the Ni enriching on the surface of products which enhances the efficiency of active component. These catalysts exhibit significantly high catalytic performance. The formation mechanism is also investigated.     

Hydrogenation of 2-methylindole using supported metal catalysts

The hydrogenation of 2-methylindole to 2-methylindoline in toluene was studied at 60 °C and 40 bar hydrogen pressure in a batch mode using a range of carbon, alumina, and zeolite supported metal catalysts were performed in toluene. The results were compared with a more conventional catalytic system containing besides 5% Pt/C also 1.2 eq. of p-toluenesulfonic acid in ethanol:water (50:50 v/v). The highest turnover frequency (TOF) was obtained a zeolite supported iridium catalyst.     

Catalytic synthesis of methanethiol from methanol and carbon disulfide over KW/Al2O3 catalysts

A series of KW/γ-Al₂O₃ catalysts with varying K/W mole ratio were prepared for the synthesis of methanethiol from carbon disulfide and methanol, and characterized by N₂ adsorption–desorption, XRD and NH₃/CO₂-TPD techniques. Experimental results showed that the acidic and basic property of the catalyst plays a key role on the catalytic performance. It is shown that the conversion of CH₃OH is chiefly related to the acid sites, while the base sites of catalysts are favorable for the selectivity toward CH₃SH and hydrocarbons, but the strong base sites will restrain the selectivity toward CH₃SH. When the K/W mole ratio is K/W = 2/1 and the reaction temperature is at 603 K, the conversion of CH₃OH and the selectivity toward CH₃SH are 98.3 and 56.2%, respectively.     

Effect of cation location on the hydrothermal stability of rare earth-exchanged Y zeolites

NaY zeolites ion-exchanged with rare earth (RE) cations (La^3 +, Ce^3 +, Pr^3 +, Nd^3 +) were prepared by a double-exchange double-calcination method. The position, occupation and coordination of the zeolite extra-framework RE cations were identified by powder X-ray diffraction with the Rietveld refinement. The results indicate that Ce species were insusceptible to migration into the sodalite cages compared with others under the same circumstances, which may be attributed to the facile formation of CeO₂(IV) based on Ce(OH)^2 + and oxygen as well as the retarded migration of tetravalent cerium. Furthermore, the stability and activity of REY zeolites increased with decreasing ionic radii of RE elements.     

Effects of steaming-made changes in physicochemical properties of Y-zeolite on cracking of bulky 1,3,5-triisopropylbenzene and coke formation

The effects of acidic properties and structural changes of Y zeolite, produced by steaming, on the zeolite cracking activity, coking tendency and distribution of various products during catalytic conversion of bulky 1,3,5-triisopropylbenzene (TIPB) are reported. NaY zeolite with framework Si/Al ratio of 2.4 was synthesized by a hydrothermal method and ammonium exchanged. The zeolite was dealuminated by a temperature-programmed steaming to form USY1 and USY2 zeolites with framework Si/Al ratio of 8.1 and 12.3 respectively. The catalysts were characterized by XRD, XRF, SEM, AAS, NH₃–TPD and N₂ adsorption–desorption techniques. The samples were in-situ activated at 748 K and evaluated by TIPB cracking at 623 K. The coke content of the catalyst beds was estimated by TPO using an FT-IR gas cell. The results of activity measurements reveal that the dealuminated zeolites lead to lower cracking activity initially; while, they exhibit higher activity at longer times. In addition, a slight modification of the window diameter of Y zeolite, as revealed by pore size distribution analyses, alters the diffusion limitation of the reactant and products through the pores of the zeolite and significantly affects the adsorbent–adsorbate interactions. TPO experiments show that compared to the precursor zeolite, lower amount of coke is formed on the dealuminated catalysts possessing lower density of acid sites. However, the coke formed on USY samples is heavier than that formed on its precursor Y zeolite. This may be attributed to the larger pores shaped in the dealuminated catalysts which in turn provide suitable places for coke formation and growth.     

Zeolite H-USY for the production of lactic acid and methyl lactate from C3-sugars

Lactic acid is an interesting platform chemical with many promising applications. This includes the use as a building block for the production of biodegradable plastics and environmentally friendly solvents. A study of the liquid-phase conversion of the triose-sugars, glyceraldehyde and dihydroxyacetone directly to methyl lactate and lactic acid catalyzed by inexpensive commercially available zeolites is presented. One particular zeolite, H-USY (Si/Al = 6) is shown to be quite active with near quantitative yields for this isomerization. Deactivation of the H-USY-zeolite was studied by correlating the catalytic activity to data obtained by TPO, XRD, N₂-sorption, and NH₃-TPD on fresh and used catalysts. Coking and irreversible framework damage occurs when lactic acid is produced under aqueous conditions. In methanol, methyl lactate is produced and catalyst deactivation is suppressed. Additionally, reaction rates for the formation of methyl lactate in methanol are almost an order of magnitude higher as compared to the rate of lactic acid formation in water.     

Ammonolysis of ethanol on pure and zinc oxide modified HZSM-5 zeolites

Reaction between ethanol and ammonia have been studied on various zinc oxide modified HZSM-5 (Si/Al=225) catalysts under various conditions of temperature, C/N ratio of the reactants and their WHSV. Two pure zinc oxides were taken for the study. One was a highly active acidic form Z₁ and the other was a stoichiometric non acidic zinc oxide Z₂. The activity of the catalysts for ammonolysis reaction followed the order Z₂⪡Z₁⪡HZSM-5. However, for composite catalysts containing 10–40% Z₁ on HZSM-5, the activity increased synergistically and became maximum (∼81% conversion of alcohol) for the catalyst 40% Z₁/HZSM-5 and about 50% conversion for the catalyst 40% Z₂/HZSM-5. The products formed were mainly N-heterocycles. Some novel high molar mass N-heterocycles were also detected. The catalytic activity and product selectivity was crucially affected by the reaction conditions, particularly the effect of temperature; the optimum yield of the products was obtained at the catalyst temperature of 723 K, C/N ratio 0.3892 and WHSV of 2.5 h⁻¹.