Surface Of ZSM-5 Research Articles

Reaction of butyraldehyde formation from ethylene and ethylene oxide on ZSM-5 surface

A recently discovered surface reaction of ethylene oxide (EO) with ethylene yielding butyraldehyde (BA) was studied on ZSM-5 zeolites with different contents of Al, Na, and Fe in the temperature range of -25 to 100 C. Products formed on a zeolite as a result of EO and ethylene transformations were extracted from the surface and identified using gas chromatography, gas chromatography- mass spectrometry, and nuclear magnetic resonance. In addition to BA, the other major reaction products are acetaldehyde and dioxane. Product distribution strongly depends on the composition of the zeolite samples and experimental conditions. Varying of the Al content in the zeolites as well as their temperature pretreatment showed that a key role in the formation of BA play dehydroxylated Al-contained sites. Possible transformations of EO and ethylene on the zeolite were analyzed by quantum-chemical calculations.

Controlled surface properties of Au/ZSM5 catalysts and their effects in the selective oxidation of ethanol

The catalytic activity of gold supported on ZSM5 (Au/ZSM5) was investigated for the selective oxidation of ethanol in the presence of excess oxygen. Au/ZSM5 catalyst pretreated by nonthermal O2 plasma method showed the best oxidative activity compared to low-temperature calcination in air and high-temperature reduction in hydrogen atmosphere. Results from microscopy and X-ray diffraction characterizations proved that plasma pretreatment afforded a small Au particle size and a uniform dispersion of Au nanoparticles on ZSM5 surfaces. Characterization results further demonstrated that the residual ammonia adsorbed on ZSM5 surfaces during the precipitation can be oxidized to nitrate ions by nonthermal O2 plasma treatment, while it converted to NO+ by low-temperature oxygen calcination and was completely removed by high-temperature hydrogen reduction. Dissimilar surface/interface properties caused the tremendously different interaction between gold nanoparticles and zeolite support, and consequently the catalytic performances in ethanol oxidation. In particular, under the nonthermal O2 plasma pretreatment, the formed NO3− species lowered the acidity of ZSM5 surfaces as well as anchored the Au nanoparticles, resulting in nearly 100% selectivity toward selective oxidation instead of acid-catalyzed reactions even under high reaction temperature.

Atomic Layer Deposition of ZnO Thin Films on ZSM-5 Zeolite and Its Catalytic Performance in Chichibabin Reaction

A series of ZnO thin film modified ZSM-5 zeolites was prepared by atomic layer deposition (ALD) method with different ALD cycle numbers. These samples were characterized by nitrogen adsorption–desorption, ICP-AES, XPS, TEM and NH3-TPD techniques. The results of these characterizations showed that the thin film was ZnO, which was deposited on the surface of ZSM-5, especially the edge. The surface and pores of ZSM-5 was covered progressively by the increase of ALD cycles. By relating the Zn content of each cycle to the characters of ALD method, a deposition model of ZnO on ZSM-5 substrate was deduced. The surface acidity of the prepared samples can be tuned by adjusting the ALD cycle number as well. The catalytic properties of these samples were evaluated in Chichibabin reaction of acetaldehyde and ammonia. They could not only highly enhance the total yield of pyridine bases, but also could change the product distribution.

Synthesis of core–shell ZSM-5@meso-SAPO-34 composite and its application in methanol to aromatics

A core/shell-structured ZSM-5@meso-SAPO-34 composite catalyst was hydrothermally synthesized through overgrowing SAPO-34 molecular sieve on the external surface of ZSM-5.

Conversion of methane to methanol with a bent mono(μ-oxo)dinickel anchored on the internal surfaces of micropores.

The oxidation of methane to methanol is a pathway to utilizing this relatively abundant, inexpensive energy resource. Here we report a new catalyst, bent mono(μ-oxo)dinickel anchored on an internal surface of micropores,which is active for direct oxidation. It is synthesized from the direct loading of a nickel precursor to the internal surface of micropores of ZSM5 following activation in O2. Ni 2p3/2 of this bent mono(μ-oxo)dinickel species formed on the internal surface of ZSM5 exhibits a unique photoemission feature, which distinguishes the mono(μ-oxo)dinickel from NiO nanoparticles. The formation of the mono(μ-oxo)dinickel species was confirmed with X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). This mono(μ-oxo)dinickel species is active for the direct oxidation of methane to methanol under the mild condition of a temperature as low as 150 °C in CH4 at 1 bar. In-situ studies using UV-vis, XANES, and EXAFS suggest that this bent mono(μ-oxo)dinickel species is the active site for the direct oxidation of methane to methanol. The energy barrier of this direct oxidation of methane is 83.2 kJ/mol.

Catalytic combustion of volatile organic compounds over Co/ZSM-5 coated on stainless steel fibers

• A novel gradient porous Co/ZSM-5/PSSF catalyst was prepared. • The Co/ZSM-5/PSSF catalyst presents efficient activity for isopropanol oxidation. • Catalytic efficiency of Co/ZSM-5/PSSF is superior to granular Co/ZSM-5. Co/ZSM-5/PSSF (paper-like stainless steel fibers) catalyst was prepared for the catalytic combustion of volatile organic compounds (isopropanol). The cobalt oxides modified ZSM-5/PSSF catalyst was synthesized by wet impregnation method, and the ZSM-5/PSSF was prepared via secondary growth method on the surface of PSSF supports which was made by wet lay-up papermaking method and sintering process. Characterization of all the samples was carried out by means of X-ray diffraction (XRD), scanning electron microscope (SEM), energy disperse X-ray spectrometer (EDS) mapping, X-ray photoelectron spectrum (XPS), N 2 adsorption/desorption and H 2 -temperature programmed reduction (H 2 -TPR). The results of EDS demonstrated that cobalt oxides had a perfect dispersion on the surface of ZSM-5/PSSF. The performance of catalytic oxidation of single VOCs (isopropanol) was conducted over a zeolite membrane reactor based on Co/ZSM/PSSF catalysts, the experimental results showed that the 0.5 M Co/ZSM-5/PSSF-500 °C catalyst exhibited the best catalytic activity for isopropanol oxidation with 90% conversion of isopropanol at 222 °C with the feed concentration of 4.5 mg/L and GHSV of 7643 h −1 , which was much lower than that of granular Co/ZSM-5 catalyst (293 °C). The special pore structure of ZSM-5/PSSF can offer a relatively higher contacting efficiency, lower diffusion resistance and reasonable mass/heat transfer efficiency.

Synthesis of ionic liquids coated nanocrystalline zeolite materials and their application in the simultaneous determination of adenine, cytosine, guanine, and thymine

In this study, ionic liquids coated nanocrystalline zeolite based inorganic-organic hybrid materials were synthesized. Nanocrystalline ZSM-5 zeolite was prepared under hydrothermal condition in the presence of propyltriethoxysilane as an additive in the synthesis composition of conventional ZSM-5. Ionic liquids (methylimidazolium chloride and 1-butyl-3-methylimidazolium chloride) were coated on the surface of nanocrystalline ZSM-5 by the post synthesis method. For comparative study, ionic liquids coated conventional ZSM-5 based inorganic-organic hybrid materials were also prepared. Ionic liquids coated nanocrystalline ZSM-5/ZSM-5 modified electrodes were constructed for the simultaneous determination of all four DNA bases such as adenine, cytosine, guanine, and thymine. Difference in the electro-catalytic activity of the modified electrode is explained with the help of textural properties, conductivity, and density functional theory. The analytical performance of the proposed method was demonstrated in the simultaneous determination of all four DNA bases in calf thymus DNA sample.

Iron exchanged ZSM-5 and Y zeolites calcined at different temperatures: activity in N2O decomposition

ZSM-5 and Y zeolites were modified with iron by an ion-exchange method and then calcined at 773, 873, 973 and 1,073 K. The obtained materials were characterized with respect to textural parameters (low-temperature N2 sorption), structure (X-ray diffraction, UV–vis–DRS), redox properties (H2-temperature programmed desorption, TPD) and surface acidity (NH3-TPD). The obtained results have shown that the structure of zeolites influenced form, aggregation and content of the introduced iron species. In case of the FAU type structure characterized by wide pores (max. ring size, T-atoms—12) mainly iron in form of mononuclear Fe3+ cations and Fex3+Oy oligonuclear clustered species was found. On the other hand for the MFI type structure characterized by smaller pores (max. ring size, T-atoms—10) significant contribution of iron in the form of bulky Fe2O3 clusters located possibly on the outer surface of ZSM-5 was detected. Such significant differences in distribution of iron species is probably related to various mobility of iron species in the pore systems of both zeolites. The obtained materials were tested as catalysts in the process of N2O decomposition. Calcination of zeolites at different temperatures influenced neither the properties nor the activity of the obtained catalysts.

In vitro hydroxiapatite formation on the Ca doped surface of ZSM-5[Ga] type zeolite

Abstract A high SiO 2 /Al 2 O 3 ratio ZSM-5[Ga] type zeolite was synthesized. Then an ionic exchange of Na by Ca ions on the surface was performed. The in vitro bioactivity was assessed by immersing samples in Simulated Body Fluid (SBF) for different periods of time. Bonelike apatite was formed on the zeolite as early as 7 days of immersion. This indicates that this ZSM-5[Ga] zeolite with a Ca-functionalized surface is a potential material for bone tissue regeneration.

Structural Characterization and Selective Catalytic Reduction of Nitrogen Oxides with Ammonia: A Comparison between Co/ZSM-5 and Co/SBA-15

Cobalt-containing catalysts supported on ZSM-5 zeolite and mesoporous siliceous SBA-15 were prepared and characterized by nitrogen sorption, X-ray diffraction, scanning electron and transmission electron microscopies, energy-dispersive X-ray, Fourier transform infrared, ultraviolet–visible diffuse reflectance, X-ray photoelectron spectroscopies, and temperature-programmed desorption of ammonia measurement. The effect of cobalt loading ratio on the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with ammonia was investigated. The existing Brønsted acid sites contributed to the cobalt species finely dispersed within the ZSM-5 zeolite, either as isolated cobalt ions anchored at α, β, and γ sites, or as amorphous cobalt oxides enriched on the ZSM-5 surface. NOx conversion profiles of Co/ZSM-5 exhibited two peaks. The low-temperature peak (<300 °C) was induced by cobalt ions at β and γ sites, while the high-temperature peak (>300 °C) was assigned to the amorphous and crystalline cobalt oxides. With increasing cobalt content, the intensity of low-temperature peak was enhanced monotonously, and the peak position remained constant. Increasing cobalt content promoted the high-temperature peak to shift toward lower temperatures. NOx conversion profiles of Co/SBA-15 only exhibited a high-temperature peak. For Co/SBA-15, the poor dispersion of cobalt species was derived from the absence of Brønsted acid sites. The activity of Co/SBA-15 catalysts was lower than that of the Co/ZSM-5 catalysts due to inactive cobalt ions anchored on isolated Si–OH groups, and agglomerated cobalt oxides within the SBA-15 channels blocking the reactant pathway to active sites.

Role of ZSM5 Distribution on Co/SiO2 Fischer–Tropsch Catalyst for the Production of C5–C22 Hydrocarbons

Fischer–Tropsch synthesis (FTS) for the production of gasoline and middle distillates in the range of C5–C22 hydrocarbons was investigated using ZSM5-modified Co/SiO2 FTS catalysts. The Co/SiO2 catalyst was prepared by an impregnation method using a cobalt nitrate precursor in a slurry of SiO2, and theh ZSM5-modified Co/SiO2 catalyst was subsequently prepared by synthesizing ZSM5 (Si/Al ratio = 40) by in situ hydrothermal synthesis over the Co/SiO2 catalyst at different ZSM5/(Co/SiO2) weight ratios. The catalytic performance was largely altered by changing acidity and reducibility of cobalt oxides on ZSM5-modified Co/SiO2 catalysts due to the different extents of migration of cobalt oxides from SiO2 to the ZSM5 surface with different degrees of catalytic olefin cracking reaction. The ZSM5-modified Co/SiO2 catalyst with 25 wt %ZSM5 shows a maximum selectivity to C5–C22 hydrocarbons with a high CO conversion due to the smaller cobalt crystallite size possessing a high reducibility and optimum acid site dens...

Mixed matrix membranes with HF acid etched ZSM-5 for ethanol/water separation: Preparation and pervaporation performance

The mixed matrix membranes (MMMs) were prepared from crosslinked PDMS incorporated with HF acid etched ZSM-5. ZSM-5 zeolite was etched with a series of HF aqueous-acetone solution and characterized by SEM, BET, XRD and FT-IR. It was found that HF etching process was very effective for removing organic impurities in zeolite and micro-pores were observed out of the surface of zeolite particles, which enhanced the hydrophobicity and surface roughness of ZSM-5 successfully. Both tensile strength and swelling resistance of ZSM-5/PDMS MMMs increased with the rising concentration of HF solution, which can mainly be attributed to the improved zeolite-PDMS interfacial adhesion resulted from the intrusion of PDMS into micro-pores out of the ZSM-5 surface. Subsequently, the sorption experiment was performed with the results suggesting preferential sorption of ethanol by MMMs. Moreover, the sorption selectivity of ZSM-5/PDMS MMMs increased notably as the concentration of HF solution increased. The pervaporation performance of ethanol/water mixtures using MMMs was also investigated in detail. The MMMs filled with etched ZSM-5 showed much better selectivity than that filled with non-etched ones, with a little expense of permeability. It was found that with the same zeolite loading, increasing the HF acid concentration in etching process enhanced the zeolite-PDMS interfacial adhesion which promoted the ethanol selectivity of MMMs, while depressed the total permeation flux a little. In addition, both ethanol permeation and the selectivity increased with an increase of the zeolite loading from 10% to 30%. Nevertheless, excessive zeolite loading or decreasing thickness of selective layer led to the poor selectivity to ethanol. A decline of the ethanol selectivity was also observed as the feed ethanol concentration as well as feed temperature increased.

Hierarchic zeolites: Zeolite ZSM-5 desilicated with NaOH and NaOH/tetrabutylamine hydroxide

The desilication of zeolite ZSM-5 (Si/Al=31.6) was performed by the treatment with NaOH of various concentrations (0.1, 0.2, 0.5 and 1M) and with NaOH/TBAOH mixtures of various concentrations and ratios between both bases. The information on the composition of both bulk and surface was obtained by ICP-OES and XPS, respectively. It has been found that diluted NaOH solutions extracted Si equally from the surface and bulk of ZSM-5. In more concentrated NaOH the desilication from the bulk was more effective than from the surface. The MAS NMR studies showed that Si(4Si,0Al) was less stable and was removed from the zeolite structure before Si(3Si,1Al). Higher stability of Si(3Si,1Al) was explained by the repulsion of AlO4- and OH−. According to the IR results the desilication, leading to mesopore formation, increased distinctly the amount of Si–OH on mesopore walls and also the contribution of acidic Si–OH–Al. Calcination of desilicated zeolite at air atmosphere resulted in a significant loss of tetrahedral Al due to the “steaming” of zeolite with water physisorbed in mesopores facilitated by lower stability of framework injured by desilication. Both NMR and IR studies suggested that the stability of Si atoms in the zeolite framework increased in the following order: (SiO)3Si–OH<(SiO)3Si–OSi<(SiO)3Si–OAl. Porosimetric experiments evidenced that the NaOH treatment produced mesopores with very broad pore size distribution (a majority of pore diameters was close to 20nm). The desilication with the NaOH/TBAOH mixtures produced mesopores of higher surface area and pore volume but of smaller diameter than with NaOH alone. We suppose that in the presence of TBAOH a larger number of narrower pores is formed, or narrow pores penetrate zeolite crystal more deeply.

Syntheses and catalytic activities of homogenous and hierarchical ZSM-5 grafted Pd(II) dicarbene complex of imidazole based ionic liquids

Pd(II) dicarbene complex of imidazole based cyclic and acyclic ionic liquids were prepared and their catalytic activities were compared in the Heck and the Sonogashira reactions of deactivated and economical bromobenzene/chlorobenzene. Acyclic Pd complex was found to be more active than the cyclic one. Geometrically optimized structures of cyclic and acyclic Pd complexes, which was computed using density functional method was able to explain the low activity of cyclic Pd complex. Further, these catalysts were grafted on hierarchical ZSM-5 surface and their catalytic activity and recyclability were investigated. Pd(II) dicarbene complex grafted on hierarchical ZSM-5 were found to be efficient and recyclable catalysts for CC coupling reactions. Catalysts were found to be stable and show negligible loss in activity even after the five cycles.

C–H bond activation of methane on M- and MO-ZSM-5 (M = Ag, Au, Cu, Rh and Ru) clusters: A density functional theory study

Density functional theory (DFT) calculations were carried out in a study of C–H bond activation of methane on [(SiH 3) 4AlO 4(M, MO)] (where M = Ag, Au, Cu, Rh and Ru) cluster models representing ZSM-5 surfaces. The following activity order of clusters with respect to their activation barriers could be qualitatively classified: Au ≫ Rh > Cu = Ru > Ag for metal-ZSM-5 clusters and Ag > Cu > Au ≫ Rh > Ru for MetalO-ZSM-5 clusters. Therefore, activation barriers based on transition state calculations showed that Ag–O–, Cu–O– and Au–O-ZSM-5 clusters (4, 5, and 9 kcal/mol, respectively) are more active than all the other clusters for C–H bond activation of methane.

A density functional theory study of C–H bond activation of methane on a bridge site of M–O–M-ZSM-5 Clusters (M = Au, Ag, Fe and Cu)

C–H bond activation of methane on a bridge site M–O–M- of ZSM-5 (M = Au, Ag, Fe and Cu) clusters has been performed by means of Density Functional Theory (DFT) calculations with the utilization of [Si 6Al 2O 9H 14(M–O–M)] 2+ (where M = Au, Ag, Fe and Cu) cluster models representing ZSM-5 surfaces. According to the activation barrier data based on TS calculations. The following activity order of clusters with respect to their activation barriers could be classified: Ag ≈ Au > Cu » Fe for Metal–O–Metal-ZSM-5 clusters. Activation barriers for C–H bond activation of methane on Au–O–Au- and Ag–O–Ag-ZSM-5 clusters are calculated as 4.83 and 4.79 kcal/mol, respectively. These values are lower than the activation barrier values for C–H bond activation on Cu–O–Cu-ZSM-5 and Fe–O–Fe-ZSM-5 which are 9.69 and 26.30 kcal/mol, respectively. Activation process is exothermic on Au–O–Au-, Cu–O–Cu-, and Fe–O–Fe-ZSM-5 clusters whereas it is endothermic on Ag–O–Ag-ZSM-5 cluster.

Oxidation of methane to methanol and formaldehyde over Co–ZSM-5 molecular sieves: Tuning the reactivity and selectivity by alkaline and acid treatments of the zeolite ZSM-5 agglomerates

Alkaline treatment of templated Na–ZSM-5 zeolites with NaOH solutions resulted in the creation of intercrystalline mesopores within the zeolite agglomerates, while preserving the micropore volume and crystallinity. It was found that the zeolite external surface area increased with increasing NaOH concentration and pretreatment time. These alkaline-treated samples were loaded with cobalt and a linear relationship between the number of cobalt oxidic species and the external surface area of the zeolite could be established. This in turn leads to a linear relationship between the ZSM-5 surface area and the amount of methanol produced over Co–ZSM-5 from methane and oxygen at 423 K. Attempts to remove extra framework alumina species by an acid treatment were successful. However, this acid treatment increased, after Co-deposition, the amount of highly dispersed Co 2+ inside the ZSM-5 channels, which resulted in a higher selectivity towards formaldehyde. The nature of the charge-compensating cation also determined the cobalt speciation. Co–H–ZSM-5 samples contained more cobalt inside the channels and were more selective towards formaldehyde formation than Co–Na–ZSM-5 samples.

Cu-ZSM-5 Zeolites for the Formation of Methanol from Methane and Oxygen: Probing the Active Sites and Spectator Species

A series of Cu-ZSM-5 zeolites was prepared by varying nature of the charge compensating cation, copper precursor, copper loading, and pH. The materials were tested for the oxidation of methane to methanol using oxygen. A linear relationship between the amount of methanol produced over Cu-ZSM-5 zeolites from methane and oxygen and a UV–Vis-NIR DRS charge transfer band at 22,700 cm−1 is reported irrespective of the synthesis route used. The absolute intensity of the 22,700 cm−1 band is always low, indicating a low number of active sites in the samples. In all studied Cu-ZSM-5 zeolites at least two copper species were present: (a) Cu–O clusters dispersed on the outer surface of ZSM-5 and (b) highly dispersed copper-oxo species inside the channels, a minority fraction in the sample. By relating catalytic activity to FT-IR data of adsorbed pivalonitrile, visualizing Cu–O particles on the outer surface of the zeolite, and subsequently adsorbed NO, indicative of the Cu–O species inside the zeolite channel, it was concluded that Cu–O species on the outer surface are not involved in the oxidation reaction, while copper inside the channels are responsible for the selective conversion of methane to methanol.

Direct Methane Oxidation to Methanol by N2O on Fe- and Co-ZSM-5 Clusters with and without Water: A Density Functional Theory Study

Density functional theory (DFT) calculations were carried out in a study of oxidation of methane to methanol by N2O on the Fe- and Co-ZSM-5 clusters. The catalytic cycle steps have been studied on model clusters ((SiH3)4AlO4M) (where M = Fe, Co). Calculations indicate very low methanol selectivity without water and increasing rate of methanol formation with water. These results are in qualitative agreement with the experimental literature. The methanol formation step is also found to be the rate-limiting step, and this result is in agreement with other theoretical work. Co-ZSM-5 cluster has a lower activation barrier when compared to that of Fe-ZSM-5 cluster (49 kcal/mol vs 53 kcal/mol). Activation barrier values decrease to 48 and 39 kcal/mol for Fe- and Co-ZSM-5 clusters, respectively, in the presence of water molecule adsorbed after the formation of a hydroxy group on the ZSM-5 surface. The methanol formation step is the most difficult reaction for both clusters with and without water.

Interaction of titanium and iron oxide with ZSM-5 to tune the catalytic cracking of hydrocarbons

In order to increase the yield of ethylene and propylene in the catalytic pyrolysis of heavy oil, ZSM-5 zeolite was modified by Fe 2O 3 and TiO 2 via pore volume impregnation. XRD, SEM, and TEM analysis indicated that the structure of the ZSM-5 remained intact after modification, and that the Ti and Fe partially entered the channels of the ZSM-5. Measurement of the number of Brønsted acid sites by n-propylamine temperature-programmed reaction and FTIR measurements showed that the Brønsted acid sites of Ti/ZSM-5 (TiO 2 loaded ZSM-5) and Fe–Ti/ZSM-5 (Fe 2O 3 and TiO 2 loaded ZSM-5) catalysts increased through the polarization function of Ti 4+. DRS, XPS, and TPR results showed that the presence of Ti species improved the dispersion of Fe species on the surface of ZSM-5, whereas Fe 2O 3 promoted the reduction of TiO 2. After modification by Fe 2O 3 and TiO 2, the acidity and reduction properties of Fe–Ti/ZSM-5 improved; such improvement led to a decrease of the apparent activation energy of isopropyl benzene cracking over Fe–Ti/ZSM-5 by about 21 kJ/mol compared with that over ZSM-5. As a result, catalyst Fe–Ti/ZSM-5 showed a better catalytic cracking performance of n-decane and isopropyl benzene than catalysts Ti/ZSM-5, Fe/ZSM-5 (Fe 2O 3 loaded ZSM-5) or ZSM-5.