Yield of gasoline-range hydrocarbons as a function of uniform ZSM-5 crystal size

Uniform ZSM-5 nanocrystals were synthesized by a single-templating procedure. The samples were then characterized by a variety of physical techniques such as XRD, SEM, BET, ICP and TPD. The dehydration of methanol over synthesized ZSM-5 zeolite was studied in a fixed-bed continuous flow reactor at 370 °C and WHSV of 2.6 gg⁻¹ h under ambient pressure. The effect of crystal size of zeolite catalysts on product distribution in methanol dehydration reaction was investigated. Good correlation was observed between catalytic performance, product distribution and size of ZSM-5 crystals. It was found that the decrease in crystal size significantly influences light olefins (ethylene and propylene) and paraffins (C₁–C₄) selectivity in methanol dehydration reaction. Furthermore, nanocrystal ZSM-5 showed long-term catalytic stability compared with conventional ZSM-5 provided that the reaction activity is strongly dependent on the crystal size in methanol dehydration process. The results indicated that crystal size significantly affects the catalyst lifetime and hydrocarbon distributions in product stream. Based on the obtained results, it is concluded that the use of uniform ZSM-5 nanocrystals improves the yield of propylene and alkyl aromatics in methanol conversion reaction at mild conditions.     

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.     

Enhanced production of high octane gasoline blending stock from methanol with improved catalyst life on nano-crystalline ZSM-5 catalyst

Methanol value addition reaction has been studied on lab-synthesized nano-crystalline ZSM-5, Si/Al = 13 (NZ) possessing particle size of ∼29–51 nm and a micro-crystalline ZSM-5 (MZ) of similar atomic ratio is also taken as standard for comparison studies. The NZ sample exhibited excellent catalytic activity to produce 50.7 wt.% of high octane (Research Octane Number = 137) gasoline blending stock rich in desired toluene and xylene components, while the undesired benzene is very low, suitable for fuel applications. The superior performance of NZ to MZ catalyst reflected in three fold increase in gasoline yield and considerably high time-on-stream performance.     

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.     

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.     

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.     

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.     

Confirmation of NH species in the framework of nitrogen-incorporated ZSM-5 zeolite by experimental and theoretical studies

Nitrogen-incorporated zeolites have drawn much attention as a new family of basic solid materials and N atoms are expected to be introduced into the frameworks of zeolites. In this study, nitrogen-incorporated ZSM-5 zeolites were prepared by temperature-programmed nitridation and their physicochemical properties were characterized by means of XRD, SEM and BET techniques. Combined a detailed IR characterization with a theoretical IR simulation, the bands relating to bridging Si–N(H)–Si groups at 1151 and 985 cm^?1 were observed in the IR fingerprint region of nitrogen-incorporated zeolites. The results confirmed that N atoms have been introduced into the framework of ZSM-5 zeolites by nitridation to form basic –NH– species, which was also supported by results of ²⁹Si MAS NMR characterization. Furthermore, the basic catalytic properties of nitrogen-incorporated ZSM-5 zeolites were evaluated by Knoevenagel condensation of benzaldehyde and malononitrile and enhanced conversion of benzaldehyde was achieved.     

High selective and stable performance of catalytic aromatization of alcohols and ethers over La/Zn/HZSM-5 catalysts

The catalytic conversions of methanol, ethanol, dimethyl ether and diethyl ether to aromatic hydrocarbons (especially benzene, toluene and xylene) were achieved over 0.8%Zn/0.6%La/HZSM-5 catalyst with a BTX selectivity as high as over 50% at reaction conditions of 710 K, WHSV 0.8 h^?1. The selectivity of BTX hydrocarbons in methanol aromatization reaction could remain 35% in 40 h.     

Methanol-to-olefins over FeHZSM-5: Further transformation of products

The catalytic activity of FeHZSM-5 was investigated for the conversion of both methanol and mixed C₃° + C₄ hydrocarbons. For methanol conversion at WHSV = 1 h^− 1 and 470 °C, 0.35% FeHZSM-5 showed increased selectivity for propylene and C₂⁼–C₄⁼ olefins by 21% and 4%, respectively, compared with HZSM-5. The selectivity of propane and butylene decreased. High temperature favored the conversion of C₃° + C₄ mixture while the selectivity of ethene + propylene achieved a maximum at 470 °C. Improved olefins selectivity for methanol conversion was attributed to FeHZSM-5 with more weak acid but less strong acid amount and to further transformation of the products.     

Tuning the mesoscopically structured ZSM-5 nanosheets for the alkylation between toluene and methanol

Mesoscopically structured ZSM-5 nanosheets were prepared as highly active catalysts for the alkylation between toluene with methanol. The results showed that the Brønsted acid sites of ZSM-5 nanosheets were mainly distributed on the external surface in aluminum-rich zeolites owing to the charge-balance between positive quaternary ammonium cation (N⁺) in C_ph-10-6-6, Na⁺ ions and negative aluminosilicate species. In addition, it revealed that high alkalinity was easier to depolymerize the Si O Si species in Aluminum-rich synthesis gel, and the high alkalinity was required for silica-rich systems to dissolve silica species in order to finish the self-assemble process, leading to ZSM-5 nanosheets with high alkalinity presenting enhanced catalytic performance. Moreover, the optimized ZSM-5-50-2.5 was effective for the alkylation between toluene and methanol with toluene conversion of up to 50%, and it was stably operated for 48 h under the harsh conditions of WHSV = 32.5 h⁻¹ with a desired stability.     

Catalytic performance and characterization of Ni-doped HZSM-5 catalysts for selective trimerization of n-butene

A series of Ni-doped HZSM-5 catalysts were prepared and the catalytic performance of these catalysts in n-butene trimerization was investigated. The Ni-loading, the Si/Al ratio of HZSM-5 and the reaction conditions (temperature, pressure and WHSV) played great influences on the catalytic performance of these catalysts in the reaction. 77.5 wt.% conversion of n-butene and 50.5 wt.% selectivity of trimers as well as 19.6 × 10^? 2 g_trimers/(g_cat h) yield of trimers were obtained on 1NiHZSM-5(320) catalyst up to 148 h at 420 °C, WHSV = 2 h^? 1 and 1.0 MPa. In addition, the physicochemical properties of these catalysts were comparatively characterized by powder X-ray diffraction (XRD), N₂ isothermal adsorption–desorption, infrared red spectroscopy (IR) and pyridine adsorbed infrared red spectroscopy (Py-IR) techniques. The doping of Ni into HZSM-5(320) modified the specific surface area and the acidity of these catalysts, which in turn affected the catalytic performance of these catalysts in n-butene trimerization. The acidic amount and the ratio of Lewis/Brönsted acid sites (L/B) on the external surface of these catalysts were close relative to the catalytic performance of these catalysts. 1NiHZSM-5(320) catalyst showed the highest catalytic performance in n-butene trimersization among the investigated catalysts because it had the proper acidic amount and the proper L/B ratio on its external surface.     

The effect of BaO and Al2O3 addition on the crystallization behaviour of cordierite glass ceramics in the presence of V2O5 nucleant

The effect of V₂O₅ nucleant on crystallization of stoichiometric cordierite glass ceramics in the presence of various amounts of BaO and Al₂O₃ additives were investigated by DTA, XRD and SEM. It was shown that 3 wt.% V₂O₅ and 1.5 wt.% BaO were the optimum amounts of the additives effective in inducing both surface and bulk crystallization in the above glass ceramics.This resulted in ～90 wt.% cordierite after a 3 h heat treatment at 1020 °C. The specimens possessing 4–5 wt.% Al₂O₃ in excess of the stoichiometric cordierite composition, developed mullite along with cordierite in the temperature range of 1045–1055 °C, whereas in the specimen containing 6 wt.% excess Al₂O₃, mullite was detected as the sole crystallization product.     

Optimization and statistical modeling of catalytic oxidation of 2-propanol over CuMnmCo2−mO4 nano spinels by unreplicated split design methodology

Optimization of 2-propanol oxidation over CuMn_mCo_2?mO₄ nanospinels was carried out by a split design method. 15-term model was proposed to fit the experimental data. The model revealed that both whole plot and subplot variables have significant effects on conversion of 2-propanol. The model predicted the interaction of subplot and whole plot variables as well as their importance. The maximum conversion of 2-propanol was observed over CuMn₂O₄ (x₁ = 0.33, x₂ = 0, x₃ = 0.67) at calcination and reaction temperatures of 800 °C (z₁ = 1) and 300 °C (z₂ = 1), respectively. The predicted response and the response obtained from experiment for optimum conditions were 93.36 and 96, respectively.     

Gas-phase selective oxidation of chloro- and methoxy-substituted toluenes on TiO2–Sepiolite supported vanadium oxides

Catalytic behaviour of vanadium oxide systems (5–20 wt.% V₂O₅) supported on TiO₂–Sepiolite (with titania loading around the theoretical monolayer, 12 wt.%, 12Ti–Sep) and, as reference, on Sepiolite calcined (Sepc) in the p-substituted toluene derivatives selective oxidation was studied. In all the catalysts studied p-chloro (p-ClBA) and p-methoxybenzaldehyde (p-MeOBA) were the main products. The yields to benzaldehydes obtained with %V/12Ti–Sep are comparable with some of those reported in the literature under similar kinetically controlled experimental conditions (S_p-ClBA = 70% and X = 19% were obtained at 653 K on 20 V/12Ti–Sep). The activity for benzaldehyde derivatives formation of the %V/12Ti–Sep systems was superior to that exhibited by the %V/Sepc systems and in both series it notably increased when vanadium loading did. Furthermore, both p-substituents favourably influenced the partial oxidation of the methyl group to the corresponding aldehyde, whose formation at isoconversion is as follows: p-ClBA > p-MeOBA > BA. A concerted reaction mechanism in the oxidation of the toluenes to benzaldehydes on polymeric vanadia species has been proposed which is able to explain the toluene substituent effects as well as the activity of the catalysts.     

Rheological study of organoclays prepared from Indian bentonite: Effect of dispersing methods

Rheological properties of the organoclays prepared by cation exchange reaction of Indian bentonite with quaternary ammonium compounds viz. Hexadecyltrimethylammonium bromide, N-cetylpyridinium chloride and Stearyldimethylbenzylammonium chloride have been investigated. The basal spacing, particle size and bulk density of organoclays were affected by the chain length and/or carbon content (organic density) of quaternary ammonium compounds. The rheological behavior study revealed that all the toluene–organoclay-dispersions exhibited shear-thinning flow behavior, degree of shear-thinning, stability of the gel structures and yield stress. The incorporation of a mixture of 5 vol.% of H₂O in methanol as polar activator studied in the range of 33 to 100 wt.% of organoclay reinforced the rheological properties, viscosity and gel volume, and the degree of shear-thinning, stability of the gel structures and yield stress of the toluene–organoclay-dispersions. The organoclays with polar activator having 65 wt.% concentration exhibited optimum rheological reinforcement. The rheological properties were found to be more enhanced by ultrasonication relative to conventional stirring/shearing. Power-law and Casson equations have been used to describe the rheological properties of toluene–organoclay-dispersions.     

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.