磷改性ZSM-5沸石的催化裂化性能

用磷改性ZSM-5沸石,并将其制备成催化剂。初步考察了其物化性能的变化,并在固定床重油微反装置上考察了其催化裂化反应特性。研究发现,磷能显著改善ZSM-5沸石的活性、稳定性和选择性。ZSM-5沸石上不同的磷含量和其与不同的Y型分子筛配伍对催化裂化反应有着显著的影响。合理调配催化裂化催化剂的活性组分,适当控制其氢转移能力和烷基化能力,对增产丙烯有着积极的意义。     

Side chain alkylation of 2-picoline with formaldehyde over alkali modified zeolites

The catalytic side-chain alkylation of 2-picoline with formaldehyde (37 wt/v) was studied over alkali and alkaline earth metal ion modified zeolites in vapor phase conditions at atmospheric pressure, and at a reaction temperature of 300°C. A mixture of vinylpyridine and ethylpyridine were formed by the alkylation of the corresponding picoline over Li, Na, K, Rb, Cs, Mg, Ca, Sr and Ba metal ion modified zeolites. The catalytic activity of side-chain alkylation of 2-picoline was studied over various alkali modified zeolite molecular sieves like ZSM-5 (SiO₂/Al₂O₃ = 30), X, Y, Mordenite and MCM-41. Alkali modified ZSM-5 (30) catalyst was found more active in side-chain alkylation of 2-picoline when compared to other zeolites. Among all these catalysts studied K modified ZSM-5 (30) and K-Cs-ZSM-5 (30) gave best conversion of 2-picoline and selectivity to vinylpyridine. Cs-ZSM-5 (30) and K-ZSM-5 (30) were employed to study the reaction parameters like reaction temperature, weight hourly space velocity, molar ratio, and time on stream for 2-picoline independently. The effects of alkali metal ion content (K, Cs) and precursors of potassium ion on catalytic activity in side-chain alkylation was studied. An attempt has been made to correlate between the basicity with the activity of side-chain alkylation. The bifunctional catalyst is required containing medium or weak acidic centers and basic centers in the side-chain alkylation, which is understood through proposed reaction mechanism. The selectivities of 2-vinylpyridine were 81.7, 90.8, and 94.8% at 65.4, 62.1 and 57.2% conversions at 300°C from 2-picoline and formaldehyde over K-ZSM-5 (30), Rb-ZSM-5 (30) and K-Cs-ZSM-5 (30) respectively. Indian Institute of Chemical technology (IICT) communication no: 020707     

The Effect of Zeolite Structure on the Activity and Selectivity in p-Xylene Alkylation with Isopropyl Alcohol

The effect of zeolite architecture and channel dimensionality on p-xylene conversion and selectivity to 1-isopropyl-2,5-dimethyl-benzene was investigated in p-xylene alkylation with isopropyl alcohol over novel zeolites SSZ-33 and SSZ-35. Catalytic behavior of these zeolites was compared with those of zeolites Beta, mordenite, ZSM-11 and ZSM-5. It was found that p-xylene conversion increases with increasing pore size and connectivity of the channel system of individual zeolites with the exception of SSZ-35, which possesses a system of one-dimensional 10-ring channels that periodically open into wide, shallow cavities circumscribed by 18-rings. SSZ-35 exhibited the highest conversion among all zeolites at the reaction temperature of 150 °C and also the highest selectivity to 1-isopropyl-2,5-dimethyl-benzene. Molecular modeling confirmed the dimensions of the 18-ring cages are optimal for the formation of this alkylation product.     

The performance of HMCM-22 zeolite catalyst on the olefin alkylation thiophenic sulfur in gasoline

The catalytic performance of the HMCM-22 zeolites with different Si/Al₂ ratios for the olefin alkylation thiophenic sulfur (OATS) process was investigated. With the Si/Al₂ ratio decreasing, the catalytic activity of the HMCM-22 zeolite was increased clearly due to the acidity increment. Further, the thiophene alkylation activity was increased much faster than the xylene alkylation and the hexene oligomerization for the reactivity difference of thiophene, xylene and hexene. When the Si/Al₂ ratio decreased from 473 to 98, the thiophene alkylation activity first reached its quasi-plateau value and its selectivity got a maximum, while after that the increased acid sites would more transfer to the hexene oligomerization and the xylene alkylation, thus improved their activity and decreased the selectivity of thiophene alkylation.     

Surface Acidity of H-Beta and Its Catalytic Activity for Alkylation of Benzene with Propylene

The acidity of H-beta zeolites with SiO₂/Al₂O₃ ratios ranging from 20 to 350 was characterized by NH₃-TPD profiles and FTIR spectra of adsorbed pyridine. As SiO₂/Al₂O₃ ratios of the H-beta zeolites increased, NH₃-TPD acidic amount of the samples is decreased. The IR bands of the adsorbed pyridine on the zeolites are also decreased with the increased SiO₂/Al₂O₃ ratios. The batch reaction of propylene and benzene was carried out in liquid phase at 423 K over H-beta zeolites. The selectivity to isopropylbenzene was high. The catalytic activity of H-beta zeolites is in direct proportion to the acidic amount of the zeolites in general. H-beta zeolite of SiO₂/Al₂O₃=27, which contains the highest amount of Brønsted acid sites as indicated by FTIR spectra of adsorbed pyridine, is the most reactive catalyst in the alkylation reaction. In continuous liquid-phase reactions, high propylene conversion and isopropylbenzene selectivity can be achieved at 413–453 K with benzene to propylene mole ratio from 4 to 8. The catalytic activity and selectivity of the H-beta zeolite do not change after 1100 h of reaction.     

Alkylation of toluene with ethene over H-ZSM-5 zeolites

It is shown that the alkylation of toluene with ethylene to give p-ethyltoluene can be conducted selectively on small crystals ( 1μ) of unmodified H-ZSM-5 zeolites to a level higher than that corresponding to a thermodynamic equilibrium composition. A comparison of the ethyltoluene isomers formed with H-Y and H-ZSM-5 zeolites at various conversions and temperatures indicates that p-ethyltoluene is preferentially formed in the channel intersections of the H-ZSM-5 zeolite, even during the initial alkylation step. The final ethyltoluene isomer composition is a result of competition between the rates of alkylation and isomerization and subsequent diffusional transport of individual isomers through the zeolite channels. Zeolite coking causes an apparent increase in the p-ethyltoluene selectivity; however, a more dramatic decrease in toluene conversion results in the formation of a considerably lower amount of p-ethyltoluene. This is caused by a partial blocking of the zeolite channel system.     

Aromatic Transformations Over Mesoporous ZSM-5: Advantages and Disadvantages

Catalytic behavior of mesoporous ZSM-5 was investigated in toluene disproportionation, toluene alkylation with isopropyl alcohol, and p-xylene alkylation with isopropyl alcohol to understand the effect of the presence of mesopores. Three ZSM-5 zeolites (conventional one and two mesoporous differing in the mesopore volume) having similar Si/Al ratio were synthesized and characterized as for their acidity (internal and external) as well as their micropore/mesopore volume. No substantial differences among three samples were observed as for the type and concentration of Brønsted and Lewis acid sites as well as their location in zeolite channels or on external surface of zeolite crystals. Conversions of toluene and p-xylene increased with increasing volume of mesopores in ZSM-5 zeolite while the selectivity to individual products depended on the type of reaction. In general, selectivity to sum of xylenes in toluene disproportionation, sum of isopropyltoluenes in toluene alkylation and to 1-isopropyl-2,5-dimethylbenzene in p-xylene alkylation increased due to a shorter contact time molecules spent in mesoporous ZSM-5 catalysts. In contrast, para-selectivity decreased as diffusion pathways were shorten due to the presence of mesopores.     

Bimetallic Zeolite Catalyst for CO2 Reforming of Methane

The catalytic activity of Ni–Rh on the synthesized BEA zeolite in carbon dioxide reforming of methane has been investigated. Catalysts were prepared using the incipient wetness impregnation method, with a total content of metals up to 5 wt%. Catalysts were characterized through XRD, TPR, N₂ adsorption, SEM, AAS, TG/DSC analyses. The prepared Ni–Rh zeolites were tested for their catalytic activity at 700 °C, at atmospheric pressure, and at CH₄/CO₂ ratio of 1. Catalytic results showed that bimetallic based zeolites exhibit high activity (CH₄ and CO₂ conversion equal to 73 and 78, respectively) but monometallic Rh catalysts were the only one stable against coke formation.     

Fe-MFI zeolite catalyzed C3 alkylation of benzene

Benzene alkylation with isopropanol has been carried out over ZSM-5 and Fe-MFI zeolites. It was observed that Fe-MFI zeolite showed a better selectivity for cumene (isopropylbenzene) andi/(i+n) propylbenzene ratio. This can be attributed to the acidity characteristic of the zeolite. The effects of variation in reaction conditions such as temperature, mole ratio of benzene/isopropanol and WHSV on the activity and selectivity of Fe-MFI are discussed.     

Selective Catalytic Reduction of NO by Ammonia over Raney‐Ni Supported Cu‐ZSM–5 I. Catalyst Activity and Stability

Composite materials containing Raney Ni and Cu‐ZSM‐5 are highly active catalysts for the selective catalytic reduction (SCR) of NO by NH₃. Their catalytic properties were studied with particular attention to the influence of moisture and SO₂ in the feed, and to effects of catalyst shaping operations. Composite materials (16–20 wt‐% zeolite) were prepared by mixing the components, with different degree of segregation in the resulting pressed particles, or by growing ZSM‐5 crystallites on the surface of leached Raney Ni, which were then exchanged with Cu ions. Catalytic tests were performed with 1000 ppm NO, 1000 ppm NH₃, 2 % O₂ in He, at 3–6.5 · 10⁵ h^–1 (related to zeolite component). With physical mixtures, the catalytic behaviour strongly depended on the mixing strategy, particles containing both Ni and zeolite being inferior to mixed Ni‐only and zeolite‐only particles. The SCR activity was promoted by 2 % H₂O in the feed, SO₂ (200 ppm) was a moderate poison at low temperatures, but indifferent or slightly promoting at high temperatures. A catalyst prepared from ZSM‐5 grown on Raney Ni, which was ranked intermediate in dry feed, was promoted to excellent performance in H₂O and SO₂ containing feed at T > 700 K and was stable for 38 h at 845 K. The results suggest that SCR catalysts containing highly active zeolites should be produced avoiding shaping operations e.g. by use of zeolite crystallites grown on wire packings.     

Isobutane/2-butene alkylation on MCM-22 catalyst. Influence of zeolite structure and acidity on activity and selectivity

The catalytic behavior of the novel MCM-22 zeolite for the continuous alkylation of isobutane with 2-butene has been investigated at a temperature of 50°C, 2.5 MPa total pressure, and a variety of olefin space velocities. At high olefin conversions the MCM-22 zeolite showed a very high initial cracking activity attributable to strong Brønsted acid sites, as well as to the existence of strong diffusional restrictions of the TMP's (formed inside the zeolite) to exit through the channels. At short times on stream (TOS), TMP's account for ca. 40% of the C₈ fraction. The olefin conversion and the cracking activity rapidly decline with TOS, while the alkylate product became richer in dimethylhexenes, indicating a predominance of 2-butene dimerization and a loss of hydrogen transfer activity as the catalyst aged. Moreover, MCM-22 gives less TMP's than large-pore zeolites (USY, beta, mordenite), but more than the mediumpore ZSM-5 at similar 2-butene conversion. The latter catalyst was much more selective for olefin dimerization than for isobutane alkylation, presumably because formation of the bulkier TMP's was strongly impeded in its smaller pores.     

Thiophene conversion under mild conditions over a ZSM-5 catalyst

Refiners are nowadays actively considering the post-treating FCC gasoline processes as a viable and less costly approach for meeting sulfur environmental regulations. Most promising catalytic desulfurization processes do not require hydrogen addition, including between others the use of zeolites as adsorbents/catalysts. This type of desulfurization leads to the formation of significant amounts of coke, requiring keeping high catalyst activity a continuous twin fluidized bed system (fluidized-bed reactor, fluidized bed regenerator). This study evaluates the catalytic conversion of thiophene and/or thiophene in n-octane mixtures. Catalytic experiments are carried out in the CREC riser simulator under mild conditions, using H-ZSM5 zeolite dispersed in a silica matrix. The experimental results obtained demonstrate a higher selective conversion of thiophene over n-octane. It is shown that thiophene conversion proceeds via ring opening and alkylation yielding H₂S, alkyl-thiophenes, benzothiophene, and coke, with no measurable thiophene saturation or dimerization reactions observed. The experimental results are also supported with an extensive thermodynamic analysis that includes all the possible thiophene conversion pathways over zeolites. On this basis and using as a reference the observable measurable species, a reaction network is proposed to represent the thiophene catalytic conversion under the suggested gasoline post treatment conditions.     

Influences of Mesoporosity Generation in ZSM-5 and Zeolite Beta on Catalytic Performance During <Emphasis Type="Italic">n</Emphasis>-Hexane Isomerization

Abstract  

Catalytic performance of Pt impregnated parent and desilicated nano-crystalline zeolites, ZSM-5 and Beta for n-hexane isomerization was studied. Difference in channel systems of the zeolites and absence/presence of mesopores therein were found to be reflected in product distributions. ZSM-5 was desilicated by NaOH and zeolite Beta with tetramethylammonium hydroxide (TMAOH.) Desilication was found to afford comparable catalytic performance to that of the parent counterpart at reaction temperature lower by 25 °C. Observed product distributions could be substantiated with characterizations such as ammonia TPD, surface area determination and SEM. Desilicated zeolite Beta was seen to be less prone to coking as deduced from the TGA study. Location of Pt with reference to proton sites within the channels and that inside the pores viz a viz external surface also have been discussed briefly.     

C2H2-SCR of NO over HZSM-5 affected by intracrystalline diffusion of NO x

The influence of particle size of HZSM-5 zeolite on selective catalytic reduction of NO by acetylene (C₂H₂-SCR) was investigated. The zeolite with nano-particle behaved considerable higher activity than the micro-particle one for the reaction. It was revealed that the large difference in the activity for the C₂H₂-SCR of NO arising from the particle size of zeolite was not caused by limited intracrystalline diffusion of the reductant, but that of NO₂, which was strongly supported by the adsorption results obtained over the zeolites.     

In-situ synthesis and catalytic activity of ZSM-5 zeolite

ZSM-5 zeolite has been hydrothermally synthesized in-situ on the external surface of calcined kaolinite in the presence of n-butylamine. This supported zeolite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and N₂ adsorption. Several synthesis variables were systematically investigated, including SiO₂ to Al₂O₃ ratio, pH, crystallization time, and crystallization temperature. After mixing the ZSM-5 with a Fluid Catalytic Cracking (FCC) catalyst, catalytic performance was evaluated by cracking vacuum gas oil (VGO) in a micro-fixed bed reactor. ZSM-5 addition was favorable for the production of light olefins by catalytic cracking of VGO.     

NO Oxidation Kinetics on Iron Zeolites: Influence of Framework Type and Iron Speciation

Zeolites having MFI, FER and *BEA topology were loaded with iron using solid state cation exchange method. The Fe:Al atomic ratio was 1:4. The zeolites were characterized using nitrogen adsorption, FTIR and DR UV–Vis–NIR spectroscopy. The catalytic activity in NO oxidation and the occurrence of NO _x adsorption was determined in a fixed-bed mini reactor using gas mixtures containing oxygen and water in addition to NO and NO₂ and temperatures of 200–350 °C. Under these reaction conditions, the NO _x adsorption capacity of these iron zeolites was negligible. The kinetic data could be fitted with a LHHW rate expression assuming a surface reaction between adsorbed NO and adsorbed O₂. The kinetic analysis revealed the occurrence of strong reaction inhibition by adsorbed NO₂. FER and MFI zeolites were more active than *BEA type zeolite. MFI zeolite is most active but suffers most from NO₂ inhibition of the reaction rate. FTIR and UV–Vis spectra suggest that isolated Fe³⁺ cations and binuclear Fe³⁺ complexes are active NO oxidation sites. Compared to the isolated Fe³⁺ species, the binuclear complexes abundantly present in the MFI zeolite seem to be most sensitive to poisoning by NO₂.     

Methanol to olefins conversion over metal containing MFI-type zeolites

A series of metal containing MFI-type zeolites were synthesized by the rapid crystallization method with in two hours. Al(III), Cr(III), Cu (II), and Fe(III) metal ions were incorporated in the structure. Pure siliceous (Al free) MFI structured zeolite was also prepared by the same procedure as used for the metallosilicate synthesis. Si/M ratio of the synthesis gel was 100 for metallosilicates aiming for high-silica zeolites. The products have been characterized by elemental analysis, specific surface area determination, scanning electron microscopy with EDX analysis, electron spin resonance, and thermal analysis. Catalytic property of the zeolites was measured for methanol to olefin conversion reaction. The results of XRD measurement showed the only crystalline phase present was that of MFI-type zeolite. E.s.r spectroscopy has been used to study the isomorphic substitution of the metal ions incorporated in the structure. The results show that Fe(III) and Cu (II) were mainly incorporated while, Cr(III) was observed to be present in non-framework sites. The amount of template occluded into the structure was determined by thermal analysis and found to be the same for metallosilicates and highly crystalline aluminum free zeolite. The results of catalytic activity showed that about 85% selectivity (based on gaseous hydrocarbon) for C₂⁼–C₄⁼ olefin was achieved in the case of iron containing synthesized high-silica zeolite as compared with 58% in the case of Al-containing zeolite catalyst.     

Catalytic oxidation of benzene with ozone over Mn ion-exchanged zeolites

Catalytic oxidation of benzene with ozone was carried out over Mn ion-exchanged zeolites at 343 K. Benzene was oxidized on Mn-Y to form CO_x without the release of organic byproducts, whereas formic acid was formed with supported manganese oxide catalysts, Mn/SiO₂ and Mn/SiO₂–Al₂O₃. Mn-Y showed higher activity and selectivity to CO₂ than other zeolite catalysts, Mn-β, Mn-MOR, and Mn-ZSM-5. Linear relationship was observed between benzene consumption, CO_x formation and ozone consumption. Formic acid adsorbed on Mn-Y catalyst was completely oxidized to CO₂ with ozone at around 343 K.     

Kinetic and catalytic performance of a BI‐porous composite material in catalytic cracking and isomerisation reactions

Catalytic behaviour of pure zeolite ZSM‐5 and a bi‐porous composite material (BCM) were investigated in transformation of m‐xylene, while zeolite HY and the bi‐porous composite were used in the cracking of 1,3,5‐triisopropylbenzene (TIPB). The micro/mesoporous material was used to understand the effect of the presence of mesopores on these reactions. Various characterisation techniques, that is, XRD, SEM, TGA, FT‐IR and nitrogen sorption measurements were applied for complete characterisation of the catalysts. Catalytic tests using CREC riser simulator showed that the micro/mesoporous composite catalyst exhibited higher catalytic activity as compared with the conventional microporous ZSM‐5 and HY zeolite for transformation of m‐xylene and for the catalytic cracking of TIPB, respectively. The outstanding catalytic reactivity of m‐xylene and TIPB molecules were mainly attributed to the easier access of active sites provided by the mesopores. Apparent activation energies for the disappearance of m‐xylene and TIPB over all catalysts were found to decrease in the order: E_BCM > E_ZSM‐5 and E_BCM > E_HY, respectively. © 2012 Canadian Society for Chemical Engineering     

Synthesis and catalytic performance of a bi-phase core-shell zeolite composite

A zeolite composite Y/Beta with core-shell structure was synthesized by adding tetraethylammonium bromide (TEABr) exchanged NaY zeolite into the pre-reacted mixture used to prepare Beta zeolite. The composite was characterized by XRD, N₂ adsorption, SEM, and FTIR spectra of pyridine. The results show that the composite is composed of a core zeolite Y and a shell of intergrown zeolite Beta crystals, representing dual microporous structures of both Y and Beta zeolites and a new mesoporous structure. The composite has a high activity in n-octane catalytic cracking because of the formation of intergrowths and the change of acidity due to the distorted interface and surface defects.