Neopentane cracking catalyzed by iron- and manganese-promoted sulfated zirconia

Cracking of neopentane was catalyzed by a sulfated oxide of zirconium promoted with iron and manganese. Reaction at 300–450°C, atmospheric pressure, and neopentane partial pressures of 0.00025–0.005 bar gave methane as the principal product, along with C₂ and C₃ hydrocarbons, butenes, and coke. The order of reaction in neopentane was determined to be 1, consistent with a monomolecular reaction mechanism and with the formation of methane andt-butyl cations; the latter was presumably converted into several products, including only little isobutylene. At 450°C and a neopentane partial pressure of 0.005 bar, the rate of cracking at 5 min onstream was 5×10^–8 mol/(g of catalyst s). Under the same conditions, the rates observed for unpromoted sulfated zirconia and USY zeolite were 3×10^–8 and 6×10^–9 mol/ (g of catalyst s), respectively. The observation that the promoted sulfated zirconia is not much more active than the other catalysts is contrasted to published results showing that the former catalyst is more than two orders of magnitude more active than the others forn-butane isomerization at temperatures <100°C. The results raise a question about whether the superacidity attributed to sulfated zirconia as a low-temperature butane isomerization catalyst pertains at the high temperatures of cracking.     

Study of the Alkylation of Phenol with Methanol on Zn(H)-Exchanged NaY Zeolites

Abstract  

The gas-phase alkylation of phenol with methanol was studied at 473 K on zeolite NaY exchanged with Zn⁺² (samples Zn(x)NaY) or H⁺ (samples Na(x)HY) cations. Zeolite NaY contained only weak and medium Lewis acid sites. The addition of Zn⁺² formed essentially strong Lewis acid sites. In contrast, the exchange of NaY with H⁺ generated Br?nsted acid sites and decreased the density of Lewis acid sites. Zeolite NaY was inactive at 473 K, but after its exchange with Zn²⁺ efficiently promoted the phenol methylation reaction. Phenol conversion and the selectivities to o- and p-cresols increased with the Zn content in the sample. The exchange of Na⁺ with H⁺ also activated the parent NaY zeolite. At similar phenol conversion levels, Na(x)HY samples formed more anisole and less cresols than Zn(x)NaY. All the Zn(x)NaY and Na(x)HY samples deactivated on stream, but the catalyst activity decay increased with the exchange degree.     

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.     

Dispersion and Solid State Ion Exchange of VCl3, CrCl3?6H2O, MnCl2?4H2O and CoCl2?6H2O onto the Surface of NaY Zeolite Using Microwave Irradiation

Transition metal/Y zeolites have been prepared by solid state ion exchange with microwave irradiation of mechanical mixtures of VCl₃, CrCl₃ ⋅ 6H₂O, MnCl₂ ⋅ 4H₂O or CoCl₂ ⋅ 6H₂O with NaY zeolite at 900 W in 10–20 min. The prepared transition metal/Y zeolites were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), simultaneous thermal analysis (STA) and surface area measurement (BET). Concentration of dispersed transition metal on zeolite was measured and results revealed that transition metal was dispersed and ion exchanged onto the surface of NaY zeolite.     

Y型分子筛微波法改性及其选择性吸附脱硫性能

通过微波法进行液态离子交换对NaY分子筛进行改性，采用静态实验对不同吸附剂的脱硫性能进行了考察，筛选出Ce(Ⅳ)-Y吸附性能最好。采用固定床技术对Ce(Ⅳ)-Y的吸附脱硫能力进行了研究，同时运用程序升温脱附法（TPD）和频率响应方法（FR）对吸附脱硫机理进行了进一步探讨。采用微波法进行离子交换改性后的Ce(Ⅳ)-Y分子筛的离子交换度与传统水热法比较有明显提高，吸附容量较NaY有显著提高。     

Catalytic activity of Co,Mo and CoMo supported on NaY zeolite: hydrodesulfurization of gas oil at high pressure

Three series of Co/NaY, Mo/NaY and CoMo/NaY zeolite catalysts with variable metal content, prepared by a conventional impregnation method, were characterized by XRD, IR spectroscopy (oxide state) and acidity measurements (sulfide state), and tested in hydrodesulfurization (HDS) of gas oil at high pressure in the temperature range 275–350°C. The combined results of surface area, XRD and IR showed that in the catalysts with high metal loading a small loss in crystallinity and a partial blockage of the zeolite supercages were produced by Mo oxide species. The number of acid sites, which was lower for the Co/NaY than for the Mo/NaY catalysts, increased with increasing Co or Mo loading, but the strength of the acid sites was stronger for the Co/NaY series. HDS specific activities of the Co/NaY and Mo/NaY monometallic catalysts reached a maximum at very low loadings of Co ( 0.10 at. nm^–2) or Mo ( 0.16 at. nm^–2) by the double action of the metal sulfide species and the strong acid sites generated on the zeolite by the Co or Mo incorporation. In the binary CoMo/NaY catalysts, the synergy between Co and Mo species was significant for high Mo contents only.     

用EDTA脱铝控制NaY沸石硅铝比的探讨

本文用EDTA作为NaY沸石的脱铝剂,制备出具有不同硅铝比的脱铝NaY沸石。考察了EDTA的加入量和pH对脱铝程度的影响。测定了脱铝沸石样品的IR吸收光谱、Cu~( )离子交换度和对水的吸附能力。结果表明,在pH=1～2条件下脱铝程度是与加入的EDTA量成线性关系,可根据需要控制脱铝NaY沸石的硅铝比。     

Suppressed hydrogen chemisorption of zeolite encaged metal clusters: discrimination between theoretical models on the basis of Ru/NaY

The effects of thermal treatment and zeolite proton concentration on the chemical state and metal particle size of zeolite Y supported ruthenium (3.0 wt%) have been investigated using H₂-TPR, H₂-TPD, TPMS, FTIR, TEM, and EXAFS. Heating in Ar of the precursor after ion exchange, [Ru(NH₃)₆]³⁺/NaY, up to 400°C leads to nearly 100% autoreduction of the ruthenium, as evidenced by H₂-TPR and TPMS. Heating in O₂ results in the formation of volatile ruthenium oxides. After autoreduction, the Ru clusters are extremely small, their coordination numbers, derived from EXAFS, are 0.6 for Ru/HY and 0.8 for Ru/NaY. Subsequent treatment at 500°C in flowing H₂ induces Ru agglomeration to particles which are about the size of the zeolite Y supercages, as indicated by TEM and EXAFS. The Ru-Ru distances are contracted compared to bulk Ru metal. Washing of autoreduced Ru/NaY with NaOH, thus removing the protons formed during autoreduction, results in Ru agglomeration to large particles (60-100 Å). Comparison of the hydrogen adsorption of Ru clusters with similar sizes of 10-15 Å reveals a marked interaction of the Ru clusters with zeolite protons. Increasing the H⁺/Ru ratio from 3 for Ru/NaY to 10 for Ru/HY, results in a suppression of hydrogen chemisorption per Ru atom by 75%. The conclusion that formation of metal-proton adducts affects the electronic structure of the Ru clusters, thus being one of the main causes of the lowering of the heat of hydrogen chemisorption, is supported by FTIR data of adsorbed CO. The most pronounced C-O vibration band in Ru/HY is located at 2099 cm^-1; this band is absent in Ru/NaY. Significant blue-shifting of the IR bands is in conformity with electron-deficiency of the Ru clusters in Ru/HY. The results confirm that adsorptive properties of zeolite encaged metal clusters can be "tuned" by other ions sharing the same cavities.     

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.     

Novel NaY zeolite-supported nanoscale zero-valent iron as an efficient heterogeneous Fenton catalyst

NaY zeolite-supported nanoscale zero-valent iron (NZVI/NaY) was synthesized by in-situ reduction of exchanged iron ions. Composition and structural characterization showed that α-Fe nanoparticles (50–100 nm) were supported on the surface of NaY zeolite. Catalytic efficiency of the composite powders was tested in degradation of potassium acid phthalate (KHP) solution (425 mg/L). At pH 3.5, the chemical oxygen demand (COD) removal ratio reached 79%. The NZVI/NaY exhibited efficient catalytic activity close to that of iron homogeneous catalyst but with less than 50% leaching of iron cations. Further, it performed well under much wider pH range (pH 1.7–5) compared to classic Fenton reagent, providing potential alternative as a novel heterogeneous Fenton catalyst for environmental remediation.     

Seeded synthesis of small polycrystalline NaY zeolite membrane using zeolite structure-directing agent and its pervaporation performance

Continuous and polycrystalline NaY zeolite membranes were synthesized successfully on porous α-Al₂O₃ tubes by zeolite structure-directing agent (ZSDA) method. This ZSDA method consists of two steps: preparation of NaY ZSDA and growth of NaY zeolite membranes with ZSDA by the secondary hydrothermal treatment. The synthesis parameters, such as aging time, aging temperature and the amount of ZSDA added, etc. were investigated. Scanning electron microscopy and X-ray diffraction technology were used to characterize the morphology and the crystal structure of the as-synthesized zeolite membranes, respectively. The results indicated that the growth of NaY zeolite membranes on the supports depended strongly on ZSDA, which could not only accelerate the formation of NaY zeolite membranes but also inhibit the transformation of NaY zeolite phase. It was also found that the prolonged aging time, the lower aging temperature and the increasing amount of ZSDA resulted in a crystal size diminution of the product, thus linking the aging process directly to the increasing number of formed nuclei. Compared with the larger crystal NaY zeolite membrane, the small crystal NaY zeolite membrane exhibited much higher separation selectivity. At 308 K, the highest separation selectivities achieved towards 1,3-propanediol/glycerol and 1,3-propanediol/glucose were 80 and 2,400, respectively.     

Vapour phase tertiary butylation of phenol over sulfated zirconia catalyst

Vapour phase butylation of phenol was carried out over a sulfated zirconia solid superacid catalyst in the temperature range 448–473 K using t-butyl alcohol as the alkylating agent. A good substrate (phenol) conversion and excellent product (para-tertiary BP) selectivity was obtained. The catalytic activity remains nearly the same on repeated use of the catalyst. Further, the catalyst was not deactivated when the reaction was carried out for a longer duration, i.e., even after several hours of reaction.     

Surface changes in Ru/KL supported catalysts induced by the preparation method and their effect on the selective hydrogenation of citral

Several 2 wt.% Ru/KL supported catalysts were prepared by various methods with different ruthenium precursors and characterized by CO and H₂ chemisorption, N₂ adsorption, TPD of NH₃, TEM and XPS. Furthermore, CO chemisorbed species have been studied by FT-IR and microcalorimetry. Characterization measurements of catalyst IWI-Ru, prepared by incipient wetness impregnation from ruthenium acetylacetonate, evidence metal nanoparticles of 1 nm placed inside the zeolite channels, thus blocking the accessibility to part of ruthenium loading inside the micropores. Catalyst prepared by treating the KL zeolite with RuCl₃·xH₂O aqueous solution (I-Ru) exhibits nanoparticles in the range 6–8 nm at the external surface and clusters smaller that 1 nm, inside the micropores. These latter do not significantly affect the diffusion of probe molecules through the channels. Catalytic performances in the selective hydrogenation of citral in the liquid phase, at 323 K and 5 MPa, show that IWI-Ru is less active than I-Ru, but more selective towards unsaturated alcohols. Furthermore, for IWI-Ru, selectivity increases with the increasing conversion. On the other hand, removal of acid sites of the I-Ru catalyst enhances the hydrogenation activity and increases the selectivity towards citronellal. All these results are analyzed and discussed in terms of the size, shape and location of ruthenium particles in the catalysts, as well as of the metal–support interaction.     

A structured catalyst: Noble metal supported on a plate-type zirconia substrate prepared by anodic oxidation for steam reforming of hydrocarbon

A structured catalyst: noble metal supported on a plate-type zirconia substrate was prepared by subjecting a zirconium plate to a process consisting of anodic oxidation in an oxalic acid bath and calcination in the air, followed by rhodium or ruthenium component deposition by the dipping treatment. The catalytic performances of the prepared catalysts were evaluated for steam reforming of n-butane and propane. The substrate surface was significantly corroded by the anodic oxidation and calcination, and a rugged zirconia layer about 100 μm thick was formed. The crystalline state of zirconia was mainly monoclinic and tetragonal. In steam reforming of n-butane, the structured ruthenium catalyst had some activity, while the activity of the rhodium catalyst exceeded that of the commercial catalyst. For the rhodium catalyst, its reforming activity was improved by changing the temperature of dipping bath and the number of dips for adjustment of the rhodium deposition state. The rhodium catalyst prepared by dipping twice at a bath temperature of 25 °C has the largest metal surface area and a higher metal dispersion, which were thought to be the causes for the high performance. In steam reforming of propane, the rhodium catalyst showed a significantly higher activity than the commercial catalyst. The rhodium catalyst was less prone to deterioration of activity due to n-butane and propane reforming.     

Alumina supported Pt(1%)/Ce0.6Zr0.4O2 monolith: Remarkable stabilization of ceria–zirconia solution towards CeAlO3 formation operated by Pt under redox conditions

A structured Pt(1 wt%)/ceria–zirconia/alumina catalyst and the metal-free ceria–zirconia/alumina were prepared, by dip-coating, over a cordierite monolithic support. XRD analyses and Rietveld refinements of the structural data demonstrate that in the Pt supported catalysts ceria–zirconia is present as a Ce_0.6Zr_0.4O₂ homogeneous solid solution and that the deposition over the cordierite doesn’t produce any structural modification. Moreover no Pt sintering occurs.By comparing the XRD patterns recorded on Pt/ceria–zirconia/alumina and ceria–zirconia/alumina after three redox cycles, it results that Pt, favouring the structural reorganization of the ceria–zirconia into one cubic solid solution, prevents any CeAlO₃ formation. On the contrary, such phase due to the interaction between Ce³⁺ and the alumina present in the washcoat is detected when redox cycles are carried out on the ceria–zirconia metal free.Transmission electron microscopy (TEM) investigations of the redox cycled Pt/ceria–zirconia/alumina catalyst detected ceria–zirconia grains with diameter between 10 and 35 nm along with highly dispersed Pt particles (2–3 nm) strongly interacting with ceria.Scanning electron microscopy (SEM) and EDX analyses, recorded on the redox cycled Pt/ceria–zirconia/alumina washcoated monolith evidence a homogeneous distribution of the active components through the channels even after redox aging.Reduction behaviour and CO oxidation activity are in good agreement with the structural modification of the solid solution induced by the redox cycles and reflect the positive effect of Pt/ceria interaction on the catalytic performances.The effect of redox aging on the NO reduction by C₃H₆, in lean conditions, was investigated over the Pt/ceria–zirconia/alumina monolith. The catalyst shows at low temperature (290 °C) good NO removal activity and appreciable selectivity to N₂.     

H–D exchange between CD4 and solid acids: AlCl3/sulfonic acid resin, promoted and unpromoted sulfated zirconia, and zeolite HZSM-5

The H–D exchange reaction between CD₄ and each of a family of solid acids (the zeolite HZSM-5, sulfated zirconia, iron- and manganese-promoted sulfated zirconia, and AlCl₃/sulfonic acid resin) was investigated with a batch recirculation flow reactor; the data determine initial rates of the exchange reaction giving CD₃H at temperatures ranging from 440 K for AlCl₃/sulfonic acid resin to 688 and 703 K for the zeolite and promoted sulfated zirconia, respectively. Extrapolated results show that the reaction is three orders of magnitude faster with the AlCl₃/sulfonated resin (an analogue of the very strongly acidic combination of AlCl₃ and H₂SO₄) than with HZSM-5 or promoted sulfated zirconia and two orders of magnitude faster with the latter than with sulfated zirconia.     

Carbon Monoxide Hydrogenation on Cobalt/Zeolite Catalysts

The synthesis of hydrocarbons from catalytic hydrogenation of CO/H₂ was investigated over Co/zeolite catalysts at 1 atm, 493–553 K, H₂/CO = 2, and GHSV = 1200. Various zeolites, such as NaA, NaX, NaY, KL and NaMordenite, were used as the supports. The catalysts were prepared by impregnation and were characterized by H₂/CO chemisorption and temperature-programmed reduction (TPR). Based on TPD measurements, the CO/H₂ adsorption ratio can be used as an index for the extent of metal-zeolite interaction. The stronger the metal-zeolite interaction is, the higher the Co/H₂ adsorption ratio on metal is. The activity and selectivity of cobalt supported in zeolites were affected by complex factors such as framework structure, Si/Al ratio, and the complementary cations. The activity of the catalyst is in the order: Co/KL > Co/NaX > Co/NaY > Co/NaMordenite > Co/NaA. All of the Co/zeolite catalysts had a very high selectivity to C₂–C₄ olefins, which would decrease with increasing reaction temperature. Cobalt oxide supported in zeolite was difficult to reduce. Increasing the reduction temperature could increase the reducibility of cobalt and resulted in the increase of activity.     

Adsorptive Removal of Thiophene from Benzene by NaY Zeolite Ion-Exchanged with Ce(IV)

The commercial NaY zeolite with the Si/Al ratio of 5:1 was selected and modified for researching the adsorptive removal of thiophene from benzene. The zeolite was ion-exchanged in Ce(NO₃)₃ solution and then calcined in muffle to prepare the CeY sorbent. The results show that it is a suitable method to prepare the sorbent removing thiophene from benzene that NaY zeolite is ion-exchanged by cerium in Ce(NO₃)₃ solution. The desulfurization efficiency of CeY sorbent increases obviously comparing with NaY zeolite. The effects of the calcination temperature, calcination time, concentration of Ce(NO₃)₃ solution, ion-exchange time, and ion-exchange times on the desulfurization capacity of CeY sorbent were also studied. The results show that the optimal CeY sorbent can be obtained when NaY zeolite is ion-exchanged in 0.5 mol/L Ce(NO₃)₃ solution at 100°C for 4 h, calcined at 700°C for 2 h, and repeated the above steps two times. The results of XRD and BET characterization indicate that those preparation conditions mainly influence on the crystallinity, specific surface area of CeY sorbent. The best CeY sorbent can remove thiophene to 136.8 mg/L from 550.0 mg/L in thiophene-benzene solution at ambient temperature and pressure with the agent-liquid ratio of 1:16 (g/mL).     

Characterization and catalytic activity of zeolite NaY supported iridium catalysts

Two catalysts were prepared (ca. 1 wt% Ir), one with metal particles located on the external surface of zeolite NaY and the other with metal particles located inside the zeolite supercages. The two catalysts exhibited very different activities and selectivities for the hydrogenolysis of n- butane, with the Ir in NaY catalyst much less active and less selective (53% ethane) than the Ir on NaY catalyst (83% ethane). The differences in catalytic activity and selectivity between Ir on NaY and Ir in NaY are attributed to differences in the size of the active metal particle, an ensemble effect, and not to the location (encagement) of the particle. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pore-volume and surface area in microporous–mesoporous solids

To show the correct evaluation of pore-volume and surface area in microporous–mesoporous samples a series of mechanical mixtures of microporous zeolite NaY and mesoporous γ-alumina was prepared. The nitrogen adsorption isotherms (77 K) were analyzed by the modified (three parameters) BET equation and compared with the independent textural information obtained (a) from t-plots (with the standard isotherm of nonporous α-alumina and the standard isotherms of Lecloux–Pirard); and (b) by subtracting the isotherm of the parent NaY from mixed sample isotherms.For illustration, the failure of the classic (two-parameter) BET equation for samples of that type was demonstrated.