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.     

Thermal-catalytic degradation kinetics of polypropylene over BEA,ZSM-5 and MOR zeolites

In this study, thermal degradation of additive-free polypropylene powder over different type of zeolite catalysts was investigated. BEA, ZSM-5 and MOR with different surface areas, pore structures, acidities and Si/Al molar ratios were used as solid catalysts for degradation of polypropylene (PP). Degradation rate of the PP over zeolites was studied by thermogravimetric analysis (TGA) employing four different heating rates and apparent activation energies of the processes were determined by the Kissinger equation. The catalytic activity of zeolites decreases as BEA > ZSM-5a (Si/Al = 12.5) > ZSM-5b (Si/Al = 25) > MOR depending on pore size and acidity of the catalysts. On the other hand, initial degradation is relatively faster over MOR and BEA than that over both ZSM-5 catalysts depending on the apparent activation energy. It can be concluded that acidity of the catalyst is the most important parameter in determining the activity for polymer degradation process as well as other structural parameters, such as pore structure and size.     

Characterization and application of a Pt/ZSM-5/SSMF catalyst for hydrocracking of paraffin wax

The microstructured Pt/ZSM-5/SSMF catalysts, for hydrocracking of paraffin wax, have been developed by impregnation method to place Pt onto thin-sheet ZSM-5/SSMF composites obtained by direct growth of ZSM-5 on the sinter-locked stainless steel microfibers (SSMF). The best catalyst is the one with ZSM-5 having a SiO₂/Al₂O₃ weight ratio of 200, delivering ~ 95% conversion with 77.5% selectivity to liquid products or 64.4% selectivity to naphtha at 280 °C. This new approach is capable of increasing the naphtha selectivity with high activity maintenance in comparison with the literature catalysts.     

NO reduction over nanostructure M-Cu/ZSM-5 (M: Cr,Mn, Co and Fe) bimetallic catalysts and optimization of catalyst preparation by RSM

The selective catalytic reduction (SCR) of NO with NH₃ in the presence of oxygen over a series of H-ZSM-5 supported transition metal oxides (Co, Mn, Cr, Cu and Fe) was investigated. Among them, Cu/ZSM-5 nanocatalyst was found to be the most promising catalyst based on activity. The modification of Cu/ZSM-5 by adding different transition metals (Co, Mn, Cr and Fe) to improve the efficiency of NO conversion was studied. The results indicated that the Fe–Cu/ZSM-5 bimetallic nanocatalyst was the highest active catalyst for NO conversion (67% at 250 °C and 93% at 300 °C). Response surface methodology (RSM) involving central composite design (CCD) was employed to evaluate and optimize Fe–Cu/ZSM-5 preparation parameters (Fe loading, calcinations temperature, and impregnation temperature) in SCR of NO at 250 °C. The optimum condition for maximum NO conversion was estimated at 4.2 wt.% Fe loading, calcinations temperature of 577 °C and impregnation temperature of 43.5 °C. Under these condition, experimental NO conversion efficiency was 78.8%, which was close with the predicted value (79.4%).     

Photocatalytic reduction of Cr(VI) to Cr(III) in solution containing ZnO or ZSM-5 zeolite using oxalate as model organic compound in environment

Photocatalytic reduction of Cr(VI) to Cr(III) in aqueous solution containing ZnO or ZSM-5 zeolite under ambient condition was studied by using oxalate as model organic compound in the natural environment. ZSM-5 zeolite was characterized by X-ray diffraction (XRD), and point of zero net proton charge (PZNPC) titration. The effect of illumination time, mass content of catalyst (m/V), Cr(VI) initial concentrations, pH, ionic strength, and oxalate concentrations on the photocatalytic reduction of Cr(VI) was determined. The results indicate that the PZNPC of ZSM-5 zeolite is at pH 3.6 ± 0.1. At C[Cr(VI)_(initial)] = 2.00 × 10^?4 mol/L, pH 7.5 ± 0.1 and after illumination time of 24 h, the reduction of Cr(VI) were 1.1 × 10^?5 mol/L (no ZSM-5 zeolite, 4.0 × 10^?3 mol/L oxalate) and 1.0 × 10^?5 mol/L (0.4 g/L ZSM-5 zeolite, no oxalate), respectively; whereas the reduction of Cr(VI) achieved 1.0 × 10^?4 mol/L in the presence of 0.4 g/L ZSM-5 zeolite and 4.0 × 10^?3 mol/L oxalate. The removal of Cr(VI) from solution is dependent on pH value. The results are important for the application of zeolites in the treatment of Cr(VI) polluted solution in the natural environment.     

Internal versus external surface active sites in ZSM-5 zeolite: Part 2: Toluene alkylation with methanol and 2-propanol catalyzed by modified and unmodified H3PO4/ZSM-5

Vapor-phase methylation of toluene with methanol and isopropylation of toluene with 2-propanol has been investigated in a down flow reactor under atmospheric conditions using N₂ gas carrier over a series of surface modified and unmodified ZSM-5 (Si/Al = 60–170) loaded with H₃PO₄, differing in the external surface treatment of the zeolites. The feed molar ratios of toluene/methanol and toluene/2-propanol were varied over a wide range (8–0.125), and the optimum feed ratio of toluene/alcohol was less than 0.5 in both cases. Space velocity employed in toluene methylation reported as WHSV (toluene) = 1.2 h⁻¹, and the space velocity employed in toluene isopropylation reported as WHSV (toluene) = 0.8 h⁻¹. The methylation reactions were carried out in the temperature range of 623–773 K, and the isopropylation reactions were carried out in the temperature range of 483–583 K. Atmospheric pressures was maintained in all runs. Catalysts containing 0–4.9 wt.% P were prepared using modified and unmodified ZSM-5 zeolites, and their catalytic performance for vapor-phase alkylation of toluene with methanol and 2-propanol were investigated. The optimum phosphorous content for methylation was 2.1 wt.% P which was greater than the optimum phosphorous loading for isopropylation (0.7 wt.% P).     

Preparation of supported skeletal Ni catalyst and its catalytic performance on dicyclopentadiene hydrogenation

Preparation and catalytic performance of skeletal Ni catalysts supported on Al₂O₃ were studied. The effects of alloy powder/pseudo-boehmite powder mass ratios and calcination temperatures of precursors on surface properties, compressive strength and catalytic performance were investigated. It was found that catalysts prepared by precursors which were molded with alloy powder/pseudo-boehmite powder mass ratio of 4/6 and calcinated at 860 °C in air atmosphere exhibited excellent compressive strength (16.11 N/mm), high dicyclopentadiene conversion (> 95%) and appropriate THDCPD selectivity (> 50%) during 1000-hour evaluation. The operational conditions were obtained as following: T = 120 °C, P = 2.0 MPa, LSHV = 2.0 h^− 1 and hydrogen–oil ratio = 300:1.     

Role of acidity of catalysts on methane combustion over Pd/ZSM-5

Palladium-based catalysts were prepared by the impregnation (I) and ion-exchange method (E) with ZSM-5 and γ-Al₂O₃ as support respectively. The high activity of Pd/ZSM-5(I) and Pd-ZSM-5(E) catalysts for methane combustion was observed. The order of activity is consistent with Brønsted acidity of catalysts: Pd/ZSM-5(I) > Pd-ZSM-5(E) > Pd/Al₂O₃. It is shown by FT-IR that methane adsorbs on acidic bridging hydroxyl groups of ZSM-5-supported Pd catalysts. Symmetric v₁ C–H stretching vibrations of methane shift to low frequency due to the interaction between methane molecules and Brønsted acid sites or Pd²⁺, indicating that methane molecules can be activated.     

Activity and stability studies of MoO2 catalyst for the partial oxidation of gasoline

The present investigation is focused on the performance of molybdenum dioxide (MoO₂) as a catalyst for the partial oxidation of isooctane. Metallic character and high oxygen mobility exhibited by this oxide appear to enhance its catalytic activity, which can be explained in terms of the Mars–van Krevelen mechanism. An oxygen-to-carbon ratio (O/C) of 0.72 seems to stabilize the catalytic performance, which could reach H₂ yields of 78% and carbon conversions of 100%, at 700 °C and 1 atm, after 20 h on stream. In addition, the catalyst was tested for sulfur tolerance using thiophene as model sulfur compound. Our findings indicate that the catalytic activity is barely affected even at sulfur concentrations as large as 500 ppm, after 7 h on stream. Finally, the catalyst performance was compared to that of a nickel catalyst using premium gasoline as fuel. MoO₂ displayed a stable performance whereas the Ni catalyst deactivated due to coke formation.     

Storage of molecular hydrogen into ZSM-5 zeolite in the ambient atmosphere by the sealing of the micropore outlet

The storage of molecular hydrogen into ZSM-5 zeolite in the ambient atmosphere was examined by hydrogen filling into the micropore and the following sealing of the micropore outlet to prevent the release of hydrogen to the outside. The surface grafting of 1,4-bis(hydroxydimethylsilyl)benzene onto ZSM-5 zeolite was applied to the sealing of the micropore outlet. Pressurized hydrogen (10 MPa) was filled into the micropore of ZSM-5 at liquid nitrogen temperature (−196 °C), and then the sample was heated at 150 °C for forming strong binding between the zeolite surface and the disilane compound under the hydrogen pressure. The hydrogen sorption isotherm at −196 °C showed that the adsorption of hydrogen onto the disilane-grafted ZSM-5 thus obtained was reduced to less than 20% from the original ZSM-5. The remarkable hysteresis between the adsorption and desorption branches of the isotherm indicated that the kinetic trap of hydrogen occurred by the narrowed outlets of the micropores of ZSM-5 with the disilane compound. Even after exposing the disilane-grafted ZSM-5 to the atmosphere over a few months, hydrogen could be discharged by heating over 150 °C. This result demonstrated that molecular hydrogen was successfully stored into ZSM-5 zeolite in the ambient atmosphere for a long time.     

Effect of addition of surface modified nanosilica into silica–zirconia hybrid sol–gel matrix

An organic–inorganic hybrid sol (MZ) comprising a methacrylate functionalized silane matrix (M) and zirconium-n-propoxide (Z) was prepared using sol–gel technique. Two methodologies were adopted to modify the hybrid sol for generating nanocomposite coatings viz., (a) addition of acrylic surface modified silica nanoparticles (N) of diameter ～20 nm to the sol to enhance their compatibility with the hybrid sol–gel matrix and (b) in-situ formation of a three dimensional silica network by addition of tetraethoxy silane (T) to the sol MZ. In the first methodology, the sols were prepared with six different weight ratios of the nanoparticles to the sol, i.e. 0, 0.01, 0.05, 0.1, 0.25 and 1 which were labelled as MZ+Nx where x=0, 1, 2, 3, 4 and 5 respectively. The prepared sols were dip coated on 100 mm×100 mm polycarbonate substrates followed by thermal curing at 130 °C. The coatings were characterized for their mechanical properties like pencil scratch hardness, scratch resistance using scratch tester, nanoindentation hardness, and abrasion resistance as well as visible light transmittance. FT-IR studies were also carried out on heat-treated gels derived from the sols. A maximum pencil scratch hardness of 3H was obtained for the MZ+T coatings and these coatings withstood a critical load of 4.3±0.7 N before failure during scratch test. The maximum nanoindentation hardness of 3.8±0.01 GPa was obtained for the MZ+N5 coatings. The abrasion resistance of MZ+T coatings was higher when compared to MZ+N0 and MZ+N5 coatings. The scratch and nanoindentation hardness were seen to be better for an in-situ formed –Si–O–Si– network in the hybrid sol when compared to those obtained from coatings generated by external addition of acrylic surface modified silica nanoparticles. The difference in properties was attributed to the level of interaction between the nanoparticles and hybrid sol–gel matrix.     

Preparation and application of Ba/ZSM-5 zeolite for reaction of methyl vinyl ether and methanol

The ZSM-5 zeolite is widely used to catalyze the reactions of methanol to olefins. Herein, we have prepared the H-ZSM-5 doped with barium (Ba/ZSM-5) using incipient wetness impregnation method. The Ba modified catalysts were used to catalyze a new reaction of methanol with methyl vinyl ether to improve the selectivity of ethylene and propylene (C₂⁼ + C₃⁼). The reaction catalyzed by Ba doped H-ZSM-5 shows higher propylene selectivity over H-ZSM-5. The reaction mechanism is discussed.     

Synthesis and characterization of partially crystalline nanosized ZSM-5 zeolites

Partially crystalline nanosize ZSM-5 with high surface area (678 m²/g) was synthesized successfully without using organic template by a two-step temperature process. Aluminum nitrate was used as aluminum source for the first time to synthesize ZSM-5 materials. The presence of MFI structure of the materials was analyzed by XRD, FTIR, Raman spectroscopy and TEM techniques. Addition of commercial HZSM-5 as a seeding agent to the reactants resulted an increase in crystallinity of the ZSM-5 sample and subsequent decrease in specific surface area. The partially crystalline samples exhibited low microporosity and remarkably high meso/macropore volume with pore diameters around 30 nm.     

Photocatalytic reduction of CO2 to energy products using Cu–TiO2/ZSM-5 and Co–TiO2/ZSM-5 under low energy irradiation

Copper or cobalt incorporated TiO₂ supported ZSM-5 catalysts were prepared by a sol–gel method, and then were characterized by XRD, BET, XPS and UV–vis diffuse reflectance spectroscopy. Ti^3 + was the main titanium specie in TiO₂/ZSM-5 and Cu–TiO₂/ZSM-5, which will be oxide to Ti^4 + after Co was doped. With the deposition of Cu or Co, the efficiency of the CO₂ conversion to CH₃OH was increased under low energy irradiation. The peak production rate of CH₃OH reached 50.05 and 35.12 μmol g^− 1 h^− 1, respectively. High photo energy efficiency (PEE) and quantum yield (φ) were also reached. The mechanism was discussed in our study.     

Co(II) coordinated metal-organic framework: An efficient catalyst for heterogeneous aerobic olefins epoxidation

An 8-connected, linear trinuclear cluster-based microporous metal organic framework (NH₄)₂[Co₃(Ina)(BDC)₃(HCOO)] (denoted as Co₃InaBDC₃, Ina = isonicotinate and BDC = 1,4-benzenedicarboxylate, CCDC is 935147) had been successfully synthesized by a facile hydrothermal synthesis method. The compound was extended through BDC linkers breadthwise and Ina linkers lengthways to the highly-connected framework. The Co₃InaBDC₃ was characterized through FT-IR, N₂ adsorption, XRD, TGA and SEM, and its characteristic structure was elucidated by single crystal X-ray diffraction. Using O₂ as oxidant, the Co₃InaBDC₃ was investigated as a good performed heterogeneous catalytic material for cyclooctene epoxidation. An extremely high turnover frequency (1370 h^− 1) for epoxycyclooctane was achieved, and Co₃InaBDC₃ exhibited excellent stabilities in 5 recycles without any loss of its catalytic performance.     

The performance of CNT as catalyst support on CO oxidation at low temperature

A carbon nanotube (CNT) was used as catalyst support impregnated with transition metal cobalt for CO oxidation at low temperature. Catalyst properties were analyzed by X-ray powder diffractometer (XRD), X-ray photoelectron spectrometer (XPS), and transmission electron microscope (TEM). Analytical results for TEM and XRD demonstrated that cobalt particles were highly dispersed on the carbon nanotube (20–30 nm) with nanosized cobalt particles (10–15 nm). These investigations indicated that Co/CNT generates about 99% of the high activity for CO conversion at 250 °C and thermally stability that is superior to Co/activated carbon (AC). The optimum reaction conditions for CO conversion were O₂ concentration 3%, operation temperature 250 °C, CO concentration 5000 ppm, and space velocity 156,000 h⁻¹. At 250 °C, CO may act as a reductant for NO reduction over Co/CNT in the presence of oxygen, whereas CO/NO = 2.5 showed that maximum NO reduction was 30%. Under H₂ rich conditions, the optimum reaction temperature for CO conversion was under 300 °C, and performance of CO₂ selectivity was better at 200 °C than 250 °C as the oxygen concentration increased.     

Tunable ceria–zirconia support for nickel–cobalt catalyst in the enhancement of methane dry reforming with carbon dioxide

Ceria–zirconia mixed oxides (CeZr) were glycol-thermally synthesised as nano-crystalline supports with tunable ratios for the anchoring of nickel–cobalt (Ni–Co) catalyst to enhance methane dry reforming (MDR) reaction with carbon dioxide. High conversion of methane (90%) and carbon dioxide (92%), good output (H₂ = 32%; CO = 44%), and selectivity and stability of syngas prove the effectiveness of the catalyst deposited on this support. 80:20 for Ce:Zr was identified as the optimal ratio to attain active and stable catalytic performance in MDR, with a low coking content of 0.47 wt.%.     

Ni-ZSM-5 catalysts: Detailed characterization of metal sites for proper catalyst design

Nickel was introduced in ZSM-5 zeolite by two different methods: dry impregnation and ionic exchange. Different loadings of metal, ranging from 0.4 to 6 wt% were explored. These materials were thoroughly characterized by EXAFS, TPR, acidity measurements by H/D isotope exchange and ethane hydrogenolysis. Regardless of the metal introduction method, at 0.4 wt% Ni, the Ni-ZSM-5 catalysts present only nickel located inside the zeolite channels as compensation cations. In contrast, an increase to 1 wt% nickel (via impregnation) led to its presence both inside and outside the channels.The catalytic activity of these Ni-ZSM-5 zeolites was tested in n-hexane cracking. Depending on the way the metal was introduced, it was possible to modify the n-hexane cracking activity and the selectivity toward light alkenes. Hence, a proper design of metal and acid sites could be achieved.     

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.     

A novel monolith catalyst of plate-type anodic alumina for the hydrolysis of dimethyl ether

A novel monolith catalyst of plate-type anodic alumina was applied in the dimethyl ether (DME) hydrolysis reaction system. The reactivity of the anodic alumina with hydration treatments in DME hydrolysis reaction was investigated. The preferred hydration-treated temperature was found to be 80 °C and the anodic Al₂O₃/Al monolith exhibited higher activity than the commercial Al₂O₃ in DME hydrolysis reaction. Meanwhile, the anodic Al₂O₃/Al monolith was proven to have higher MeOH effluent mole percentage with less unfavorable side reactions than the ZSM-5 catalyst. The anodic γ-Al₂O₃/Al monolith had just 0.85% coking while the ZSM-5 catalyst had 8.81% after 100 h of continuous experiments.