Conversion of ethanol over metal-exchanged zeolites

The effects of metal exchange between zeolites and alkali metals (Li, Na, K; zeolite Y, ZSM-5, T), alkaline earths (Mg, Ca, Sr, Ba; ZSM-5), transition metals (La, Ce, Cr, Mn, Fe, Co, Ni, Pd, Cu, Zn; ZSM-5) and aluminium (ZSM-5) on the conversion of ethanol were studied. Activities of the catalysts and selectivities for ethene, C₃₊ olefins, paraffins and arenes strongly depended on the cation, chosen for the modification. Only ethene was formed by alkali exchanged zeolites, the most active being Li-Y. This could be confirmed by a long-term ageing test with Li-Y pellets under semi-industrial conditions. The exchange of ZSM-5 with alkaline earths or transition metals permitted the formation of a wide variety of products, raning from high ethene to high aromatic yields. A correlation between certain product selectivities and electronegativity was only possible in a rough approximation.     

ZSM-5 supported iron catalysts for Fischer-Tropsch production of light olefin

Fischer-Tropsch Synthesis (FTS) for olefin production from syngas was studied on Fe-Cu-K catalysts supported on ZSM-5 with three different Si/Al ratios. The catalysts were prepared by slurry-impregnation method of metallic components, and were characterized by BET surface area, XRD, hydrogen TPR and ammonia TPD. Fe-Cu-K/ZSM-5 catalyst with a low Si/Al ratio (25) is found to be superior to the other catalysts in terms of better C₂-C₄ selectivity in the FTS products and higher olefin/(olefin + paraffin) ratio in C₂-C₄ because of the facile formation of iron carbide during FTS reaction and also due to a larger number of weak acidic sites that are present in these catalysts.     

In situ analysis of volatiles obtained from the catalytic cracking of polyethylene

The effects of the solid‐acid‐catalyst pore size and acidity on polyethylene catalytic cracking were examined with a comparison of the temperature‐dependent volatile‐product‐slate changes when the polymer was cracked with HZSM‐5 and HY zeolites and the protonated form of MCM‐41. Volatile‐product distributions depended on the catalyst acidity and pore size. With HZSM‐5, paraffins were detected initially, and olefins were produced at somewhat higher temperatures. Aromatics were formed at temperatures 30–40°C higher than those required for olefin production. Small olefins (C₃–C₅) were the most abundant products when HZSM‐5 and MCM‐41 catalysts were employed for cracking polyethylene. In contrast, cracking with HY produced primarily paraffin volatile products (C₄–C₈). HY pores were large enough and the acid sites were strong enough to promote disproportionation reactions, which led to the formation of volatile paraffins. Compared with the other catalysts, HZSM‐5 with its smaller pores inhibited residue formation and facilitated the production of small alkyl aromatics. Volatile‐product variations could be rationalized by a consideration of the combined effects of catalyst acidity and pore size on carbenium ion reaction pathways. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3118–3125, 2001     

Conversion of canola oil to various hydrocarbons over Pt/HZSM-5 bifunctional catalyst

Canola oil conversion was studied at atmospheric pressure over Pt/HZSM-5 catalyst (0.5 mass% Pt) in a fixed bed micro-reactor. The operating conditions were: temperature range of 400?500°C, weight hourly space velocity (WHSV) of 1.8 and 3.6 h^?1 and steam/oil ratio of 4. The objective was to optimize the amount of gasoline range hydrocarbons in the organic liquid product (OLP) and the selectivity towards olefins and isohydrocarbons in the gas product. The gas yields varied between 22–65 mass% and were higher in the presence of steam compared to the operation without steam. The olefin/paraffin mass ratio of C₂-C₄ hydrocarbon gases varied between 0.31–0.79. The isohydrocarbons/n-hydrocarbons ratio was higher with Pt/HZSM-5 (1.6–4.8) compared with pure HZSM-5 catalyst (0.2–1.0). The OLP yields with Pt/HZSM-5 (20–55 mass% of canola oil) were slightly lower compared to HZSM-5 (40–63 mass% of canola oil) under similar conditions. The major components of OLP were aliphatic and aromatic hydrocarbons. A scheme postulating the reaction pathways for the conversion of canola oil over Pt/HZSM-5 catalyst is also presented.     

Characterization of Modified Nanoscale ZSM-5 Zeolite and Its Application in the Olefins Reduction in FCC Gasoline

Nanoscale HZSM-5 zeolite was hydrothermally treated with steam containing 0.8 wt% NH₃ at 773 K and then loaded with La₂O₃ and NiO. Both the parent nanoscale HZSM-5 and the modified nanoscale HZSM-5 zeolites catalysts were characterized by TEM, XRD, IR, NH₃-TPD and XRF, and then the performance of olefins reduction in fluidized catalytic cracking (FCC) gasoline over the modified nanoscale HZSM-5 zeolite catalyst was investigated. The IR and NH₃-TPD results showed that the amount of acids of the parent nanoscale HZSM-5 zeolite decreased after the combined modification, so did the strong acid sites deactivating catalysts. The stability of the catalyst was still satisfactory, though the initial activity decreased a little after the combined modification. The modification reduced the ability of aromatization of nanoscale HZSM-5 zeolite catalyst and increased its isomerization ability. After 300 h onstream, the average olefins content in the gasoline was reduced from 56.3 vol% to about 20 vol%, the aromatics (C₇–C₉ aromatics mainly) and paraffins contents in the product were increased from 11.6 vol% and 32.1 vol% to about 20 vol% and 60 vol% respectively. The ratio of i-paraffins/n-paraffins also increased from 3.2 to 6.6. The yield of gasoline was obtained at 97 wt%, while the Research Octane Number (RON) remained about 90.     

Selective synthesis of light olefins from syngas over potassium-promoted molybdenum carbide catalysts

In the hydrogenation of CO at atmospheric pressure, unsupported molybdenum carbide catalyst produced mostly C₁-C₅ paraffins. Promotion of the catalyst with K₂CO₃ yielded C₂-C₅ hydrocarbons consisting of 80–100% olefins and reduced the methane selectivity. The selectivity of C₂-C₅ olefins among all hydrocarbon products was 50–70 wt% at CO conversions up to 70%.This work has been supported by Korean Science and Engineering Foundation through a contract 88-03-1302.     

Effects of HZSM-5 addition during catalytic cracking ofn-hexadecane on HY

Additions of HZSM-5 to HY during cracking ofn-hexadecane enhances formation of olefins in the range C₃–C₅, with concurrent suppression of hydrogen transfer processes. Ratios of branched to linear isomers are decreased for paraffins by addition of the pentasil, while the reverse is observed for olefinic products.     

Transformation of methanol to gasoline range hydrocarbons using HZSM-5 catalysts impregnated with copper oxide

Various CuO/HZSM-5 catalysts were studied in a fixed bed reactor for the conversion of methanol to gasoline range hydrocarbons at 673 K and at one atmospheric pressure. The catalysts were prepared by wet impregnation technique. Copper oxide loading over HZSM-5 (Si/Al=45) catalyst was studied in the range of 0 to 9 wt%. XRD, BET surface area, metal oxide content, scanning electron microscopy (SEM) and thermogravimetric (TGA) techniques were used to characterize the catalysts. Higher yield of gasoline range hydrocarbons (C₅-C₁₂) was obtained with increased weight % of CuO over HZSM. Effect of run time on the hydrocarbon yields and methanol conversion was also investigated. The activity of the catalyst decreased progressively with time on-stream. Hydrocarbon products’ yield also decreased with the increase in wt% of CuO. Relatively lower coke deposition over HZSM-5 catalysts was observed compared to CuO impregnated HZSM-5 catalyst.     

Development of catalysts based on pentasil-type zeolites for selective synthesis of lower olefins from methanol and dimethyl ether

Using an integrated physicochemical approach to the study of zeolites and catalysts, scientific foundations for the targeted synthesis of catalysts based on ZSM-5 type zeolites for selective production of lower olefins from methanol and dimethyl ether have been developed. The selective synthesis of the C₂₌ and C₃₌ olefins takes place on medium-strength acid sites. The domination of strong acid sites increases the extent of the secondary oligomerization, aromatization, and cracking reactions and intensifies the deactivation of the catalyst. The effects of reaction conditions (feed partial pressure and temperature) on the outcomes of the process have been investigated. High-efficiency Zn-containing catalysts based on modified pentasils and promoted with magnesium and phosphorus have been developed for C₂₌–C₄₌ olefin synthesis. These catalysts compare well with the industrial catalyst used in the Lurgi process.     

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.     

Translating clean liquid fuels synthesis with low aromatics over NaFe@C/HZSM-22 directly in CO2 hydrogenation

Fuel production is an option for valorizing CO₂, yet deficient catalysts meeting the standard fuel production has impeded progress of this promising technology. Herein, liquid fuel synthesis is rationalized over a catalyst consisting ‘C′, ‘Na’, and ‘Fe’, as in NaFe@C, configured with ZSM-22 and ZSM-5 in CO₂ hydrogenation. While the ‘Na’ and ‘C′ functioned as structural promoters on Fe to enhance CO₂ conversion and olefins synthesis, the characteristics of the zeolites facilitated oligomerization of lighter hydrocarbons. A high C₅ + selectivity was obtained over the HZSM-22 composite in CO₂ hydrogenation dominated by olefins and isoparaffins. Model reactions for exemplar oligomerization activity over the zeolites revealed ZSM-5 as highly active with selectivity towards isoparaffins and aromatic. The ‘Na’ cations induce Lewis’s acid sites (LAS) which suppresses hydrocracking during chain growth. This consistency, revealed between the model and CO₂ hydrogenation unlocks a door to zeolite usage in CO₂ hydrogenation to clean heavy hydrocarbons.     

Effect of process conditions on the composition of products in the conventional and deep catalytic cracking of oil fractions

With the purpose of increasing the yield of light C₂-C₄ olefins in comparison with that in conventional catalytic cracking, we experimentally study the effect of temperature and catalyst-to-oil ratio on the distribution of the basic products of oil catalytic cracking on the bizeolite and industrial LUX catalysts. The bizeolite catalyst contains ZSM-5 and ultrastable Y zeolites in equivalent amounts, while the LUX catalyst contains 18 wt % of Y zeolite in the HRE form. As shown by the results of our tests, the yield of C₂-C₄ olefins and gasoline in the deep catalytic cracking of hydrotreated vacuum gasoil on the bizeolite catalyst within a range of catalyst-to-oil ratios of 5–7 and temperatures of 540–560°C reaches 32–36 and nearly 30 wt %, respectively. In cracking on the LUX catalyst under similar conditions, the yield of light olefins and gasoline is 12–16 and 37–45 wt %, respectively. The distribution of target products in the deep catalytic cracking of different hydrocarbon fractions (vacuum gasoil, gas condensate, its fraction distilled from the cut boiling below 216°C, and the hydrocracking heavy residue) on the bizeolite catalyst is studied. It is shown that the fractions of gas condensate and hydroc-racking residue can serve as an additional source of hydrocarbon raw materials in the production of olefins.     

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.     

Bifunctional Catalysis of Mo/HZSM-5 in the Dehydroaromatization of Methane to Benzene and Naphthalene XAFS/TG/DTA/MASS/FTIR Characterization and Supporting Effects

The direct conversion of methane to aromatics such as benzene and naphthalene has been studied on a series of Mo-supported catalysts using HZSM-5, FSM-16, mordenite, USY, SiO₂, and Al₂O₃as the supporting materials. Among all the supports used, the HZSM-5-supported Mo catalysts exhibit the highest yield of aromatic products, achieving over 70% total selectivity of the hydrocarbons on a carbon basis at 5–12% methane conversion at 973 K and 1 atm. By contrast, less than 20% of the converted methane is transformed to hydrocarbon products on the other Mo-supported catalysts, which are drastically deactivated, owing to serious coke formation. The XANES/EXAFS and TG/DTA/mass studies reveal that the zeolite-supported Mo oxide is endothermally converted with methane around 955 K to molybdenum carbide (Mo₂C) cluster (Mo-C, C.N.=1,R=2.09 Å; Mo-Mo, C.N.=2.3–3.5;R=2.98 Å), which initiates the methane aromatization yielding benzene and naphthalene at 873–1023 K. Although both Mo₂C and HZSM-5 support alone have a very low activity for the reaction, physically mixed hybrid catalysts consisting of 3 wt% Mo/SiO₂+HZSM-5 and Mo₂C+HZSM-5 exhibited a remarkable promotion to enhance the yields of benzene and naphthalene over 100–300 times more than either component alone. On the other hand, it was demonstrated by the IR measurement in pyridine adsorption that the Mo/HZSM-5 catalysts having the optimum SiO₂/Al₂O₃ratios, around 40, show maximum Brönsted acidity among the catalysts with SiO₂/Al₂O₃ratios of 20–1900. There is a close correlation between the activity of benzene formation in methane aromatization and the Brönsted acidity of Mo/HZSM-5, but not Lewis aciditiy. It was found that maximum benzene formation was obtained on the Moz/HZSM-5 having SiO₂/Al₂O₃ratios of 20–49, but substantially poor activities on those with SiO₂/Al₂O₃ratios smaller and higher than 40. The results suggest that methane is dissociated on the molybdenum carbide cluster supported on HZSM-5 having optimum Brönsted acidity to form CH_x(x>1) and C₂-species as the primary intermediates which are oligomerized subsequently to aromatics such as benzene and naphthalene at the interface of Mo₂C and HZSM-5 zeolite having the optimum Brönsted acidity. The bifunctional catalysis of Mo/HZSM for methane conversion towards aromatics is discussed by analogy with the promotion mechanism on the Pt/Al₂O₃catalyst for the dehydro-aromatization of alkanes.     

CrHZSM-5 Zeolites – Highly Efficient Catalysts for Catalytic Cracking of Isobutane to Produce Light Olefins

The CrHZSM-5 catalysts with trace amount of Cr were firstly used for catalytic cracking of isobutane, and the effect of Cr-loading on the catalytic performances of CrHZSM-5 catalysts for the cracking of isobutane was also studied. The results suggested that when the loading of Cr in the CrHZSM-5 catalysts was less than 0.038 mmol/g Cr, especially at Cr loading of 0.004 mmol/g, both the reactivity of isobutane cracking and the selectivity to light olefins of CrHZSM-5 samples were greatly enhanced compared with the unpromoted HZSM-5, and very high yields of olefins(C₂+C₃) and ethylene were obtained. For instance, the yield of olefins(C₂+C₃) and ethylene reached 56.1% and 30.8%, respectively, at 625 °C when 0.004 mmol/g Cr was loaded on HZSM-5 sample.     

The skeletal isomerization of C4-C7 1-olefins over ferrierite and ZSM-5 zeolite catalysts

The skeletal isomerization of C₄-C₇ 1-olefins was studied on ferrierite (FER) and ZSM-5 (MFI) zeolites to elucidate the effect of the molecular distribution in zeolite pores on the selectivity foriso-olefin formation. Regardless of the difference in molecular length of 1-olefins, the FER zeolite showed high selectivity foriso-olefins, while the selectivity became slightly low at the skeletal isomerization of long olefin molecules. The drastic decrease in the selectivity of MFI zeolites by increasing the conversion is concurrently observed in the skeletal isomerization of C₄-C₇ 1-olefins. The high selectivity of FER zeolites is explained by their sparse distributions of olefin molecules in pores, which induces a high preference for monomolecular skeletal isomerization.     

Ethanol steam reforming study over ZSM-5 supported cobalt versus nickel catalyst for renewable hydrogen generation

The renewable hydrogen generation through ethanol steam reforming is one of the anticipated areas for sustainable hydrogen generation. To elucidate the role of Ni and Co with ZSM-5 support, catalysts were prepared by wet impregnation method and ethanol steam reforming(ESR) was performed. The catalysts were characterized by HR-XRD, ATR–FTIR, HR-SEM, TEM with SAED, EDAX, surface area analyzer and TPR. It had shown complete ethanol conversion at 773 K, but the selectivity in hydrogen generation was found higher for 10% Ni/ZSM-5 catalyst as compared to 10% Co/ZSM-5. The 10% Ni/ZSM-5 catalyst has about 72% hydrogen selectivity at temperature 873 K. It indicates that Ni is a more sustainable catalyst as compared to Co with ZSM-5 support for ESR. The C_2H_4 was found major undesirable products up to 823 K temperature. Nevertheless, the 10% Ni/ZSM-5 catalyst had shown its stability for high temperature(873 K) ESR performance.     

High efficient mesoporous HZSM-5 nanocatalyst development through desilication with mixed alkaline solution for methanol to olefin reaction

Methanol to olefin (MTO) process is a non-oil route for the light olefins production. We report the mesoporous and high siliceous HZSM-5 nanocatalyst development through the new desilication process including the mixed alkaline solution. The properties of nanocatalysts were characterized using TGA/DTA, XRD, ICP, FE-SEM, BET, FT-IR, and NH₃-TPD techniques. FE-SEM images represent the spherical morphology of parent nanocatalyst including smooth surface. The XRD analysis confirms that applied desilication does not change the typical MFI-type structure of ZSM-5 nanocatalysts. The BET and NH₃-TPD results show that mixed alkaline solution including 40 wt% TPAOH results in the best adjustment of textural (299.7 m²/g) and acidity (strong/weak ratio of 0.21) properties, respectively. The PHZ-NaTP0.4 nanocatalyst represents the highest methanol conversion (99.2%), propylene selectivity (48.3%), C₃ ⁼/C₂ ⁼ molar ratio (7.4) as well as lowest selectivity to C₁–C₄ alkanes (4.6%) for long time on stream (170 h). The low selectivity of light alkanes (C₁–C₄) and high total light olefins (ca. 75%) confirm the stable performance of nanocatalyst. Consequently, the developed PHZ-NaTP0.4 nanocatalyst is a high efficient MTO catalyst and can be candidate for commercial scale up.     

Effect of hydrothermal treatment temperature on FCC gasoline upgrading properties of the modified nanoscale ZSM-5 catalyst

Nanoscale HZSM-5 zeolite was hydrothermally treated with ammonia water at different temperatures and then loaded with La₂O₃ and ZnO. The parent and the modified nanoscale HZSM-5 catalysts were characterized by SEM, NH₃-TPD, IR and XRF. The performance of the modified HZSM-5 catalysts for FCC gasoline upgrading was evaluated in a fixed bed reactor in the presence of hydrogen. The results indicated that the modified catalyst which was hydrothermally treated at 400 °C exhibited excellent aromatization activity, isomerization activity and higher ability of reducing olefin content in FCC gasoline. Under the given reaction conditions, the olefin content in FCC gasoline could be decreased from 49.6 to 8.1 vol.%. The catalytic performance of the modified nanoscale ZSM-5 catalyst hardly changed within 300 h time on stream, and the research octane number (RON) of gasoline was preserved.     

Tuning millisecond chemical reactors for the catalytic partial oxidation of cyclohexane

It is demonstrated that millisecond partial oxidation of cyclohexane can be tuned by varying the catalyst and operating conditions to generate product distributions that favor (1) oxygenates, (2) olefins, or (3) syngas (H₂ and CO). High selectivities to parent oxygenates require low conversions using low-temperature catalysts, such as Ag or Co. Olefins are favored by Pt or Pt-Sn and H₂ addition eliminates the production of CO and CO₂, thereby increasing olefin selectivities. For syngas, Rh is the catalyst of choice. Finally, a Pt-10% Rh single gauze gives high selectivities to both oxygenates and olefins.Conventional methods for the partial oxidation of cyclohexane are liquid-phase processes that are plagued by poor conversions, high recycle costs, long residence times (minutes to hours), and expensive catalysts. In contrast, with a cyclohexane–oxygen feed at C₆H₁₂/O₂=2, a Pt-10% Rh single gauze catalyst can give total selectivities exceeding 80% to oxygenates and olefins at 25% cyclohexane conversion and complete oxygen conversion. The products consist of nearly 60% selectivity to the C₆ products, cyclohexene and 5-hexenal. The temperature profile attained in the single-gauze reactor allows the preservation of these highly non-equilibrium products.Alternative catalysts for cyclohexane oxidation to oxygenates and olefins include α-alumina monoliths coated with Pt, Rh, Pt-Rh, Pt-Sn, Co, Mo or Ag. The Co, Mo and Ag catalysts give very high selectivities to C₆ oxygenates but are hindered by poor conversions (<5%) of both cyclohexane and oxygen at these millisecond contact times. H₂ addition to cyclohexane oxidation feed mixtures over Pt and Pt-Sn is shown to significantly increase the selectivities to C₆ olefins while reducing the formation of CO and CO₂.Cyclohexane oxidation in air over Rh monoliths enables the production of high yields (>95%) of syngas. This process could find applications in the automotive industry as the production of hydrogen from liquid fuels becomes important.