Cumene Cracking Research Articles

Catalytic properties of V2O5/SnO2 towards vapour-phase Beckmann rearrangement of cyclohexanone oxime

Abstract V 2 O 5 /SnO 2 solid acid catalysts have been employed for the vapour-phase Beckmann rearrangement of cyclohexanone oxime to ɛ-caprolactam. Catalysts with different vanadia loading (3–15 wt%) were prepared by impregnation method and characterized by XRD, BET surface area, FTIR and 51 V NMR techniques. The surface acidic properties were determined by temperature programmed desorption and cumene cracking reaction. Under optimized reaction conditions, catalyst with 9 wt% V 2 O 5 gives the maximum amount of desired product (yield 78.8%). However, the catalysts are susceptible for deactivation due to the basic nature of the reaction products (50% deactivation in 5 h). A good correlation was obtained among the rearrangement activities of V 2 O 5 /SnO 2 catalysts, their weak plus medium acidities (usually of the Bronsted type) and structural properties.

NiMo supported acidic catalysts for heavy oil hydroprocessing

Large pore diameter Al 2O 3-SiO 2 acidic mixed oxide supports were prepared by using homogeneous co-precipitation method. The acidic properties of supports (oxide) and supported catalysts (sulfided) were chemically probed with cumene cracking (HCR) into propane and benzene at atmospheric pressure and 400 °C. NiMo supported hydroprocessing catalysts activities were also evaluated with heavy Maya crude oil. The use of acidic support is to optimize yield of high octane gasoline components, i.e. selective cracking of complex crude oil molecule. The supported fresh and spent catalysts were characterized by means of N 2 adsorption–desorption and SEM–EDX spectroscopic techniques. The results point out that deactivation takes place mainly at the entrance of pore due to coke deposition, while the depositions of vanadium and nickel sulfides mainly depend on the diameter of the pores. The results also indicated that the deactivation due to carbon deposition is carried out at initial hours of the crude oil processing. The large pore diameter catalyst contains higher amounts of deposited species, which are distributed proportionally along the extrudate radius, while for smaller pore diameter catalyst the deposition mainly occurs on the extrudate surface.

Acidity and catalytic activities of sulfated zirconia inside SBA-15

SBA-15 containing various amount (10–50 wt.%) of highly dispersed ZrO 2 is prepared using urea hydrolysis method. The sulfated zirconia (ZrO 2) in SBA-15 catalysts were prepared using these materials. The materials were characterized by XRD, BET surface area, TEM, TGA, acidity measurements using in situ IR pyridine adsorption, sulfate content and catalytic activities were studied for cumene cracking and esterification of cyclohexanol. The Brönsted acidity, catalytic activity for cumene cracking and esterification and sulfate content were found to pass through a maxima where ZrO 2 loading is 35 wt.%. The 35SZ-SBA catalysts exhibited 6.4 times higher activity for cumene cracking compared to the bulk SZ catalysts. The relationship between acidity, sulfate content and catalytic activity are discussed in the light of existing knowledge on sulfated zirconia.

Synthesis and characterization of acidic properties of Al-SBA-15 materials with varying Si/Al ratios

Al-SBA-15 of varying Si/Al ratios in the range 11.4–78.4 was synthesized using tri-block copolymer P123. The calcined materials were examined by XRD, pore size distribution, surface area, 27Al NMR spectroscopy. The acidity and acid strength distribution were studied using microcalorimetric adsorption of NH 3. The acidic properties were also examined by cumene cracking reaction as a function of Si/Al ratios. Systematic variation of acidity and activity was observed as a function of Si/Al ratio. The initial heats of NH 3 adsorption correlated well with activity indicate that acid sites with Δ H > 100 kJ/mole is responsible for cumene cracking activity. Linear correlations were obtained with total acidity and cumene cracking activities. The tetrahedral aluminum was found to be responsible for the observed acidities and catalytic activities.

Preparation of highly active AlSBA-15-supported platinum catalyst for thiophene hydrodesulfurization

The catalytic activities of various noble metals (Pt, Pd, Rh, and Ru) supported on siliceous SBA-15 and Al-containing SBA-15 (AlSBA-15) for hydrodesulfurization (HDS) of thiophene at 350°C were investigated. AlSBA-15 was prepared by a grafting method using aluminum isopropoxide (Al(OC3H7)3) hexane solution. The HDS activity of Pt/AlSBA-15 catalyst was the highest among those of various supported noble metal catalysts, and this activity was higher than that of commercial CoMo/Al2O3 HDS catalyst. The catalysts were characterized by XRD analysis, hydrogen adsorption, 2-propanol dehydration, cumene cracking, and FT-IR. Dispersion of Pt on SBA-15 was remarkably enhanced by Al grafting. It was revealed that the acidity of AlSBA-15 was higher than that of SBA-15. Furthermore, Brønsted acid sites were observed on AlSBA-15. FT-IR spectra of thiophene adsorbed on AlSBA-15 indicate that thiophene molecules interact with Brønsted acid sites on the surface of AlSBA-15 and that the strength of this interaction was stronger than that of SBA-15. Based on these results, thiophene molecules activated on Brønsted acid site of AlSBA-15 and hydrogen molecules activate to form spillover hydrogen on Pt particles in Pt/AlSBA-15 catalyst in the HDS of thiophene.

Characterization of mesoporous alumina prepared by surface alumination of SBA-15

Mesoporous aluminas of controlled pore sizes were synthesized by multiple grafting of Al isopropoxide in organic solvents on mesoporous silica SBA-15. These materials were characterized by N 2 physisorption, TEM, XRD, 27Al NMR and their surface chemical properties were probed by DRIFT, cumene cracking and MoO 3 thermal spreading. The results show that the chemical nature of the Al-grafted materials varies continuously with the number of grafting from pure silica to pure alumina. Typically, after three graftings, this original method of synthesis allows one to prepare ordered mesoporous aluminas with specific surface areas above 300 m 2 g −1 and a narrow pore size distribution centered on ca. 60 Å. In addition to the characterizations, different models were developed to understand the evolution of the specific surface area and to discard a possible pore blocking.

Hydrocracking of heavy oil using zeolites Y/Al-SBA-15 composites as catalyst supports

A series of Y/Al-SBA-15 composites were prepared by a two-step synthesis procedure in mild acidic medium. The materials were characterized by powder X-ray diffraction (XRD), N2 sorption isotherms and TEM techniques. Catalytic cracking of cumene and 1,3,5-tri-isopropylbenzene was carried out as the probing reactions on these composites. The XRD results showed that these materials are composites of Al-SBA-15 and Y zeolite. N2 sorption isotherms and TEM displayed that these composites were abundant in micropores and mesopores. At the same time, the mesopores may communicate with the␣micropores in some domains, which may result in the high catalytic activities of Y/Al-SBA-15 composites for the␣cracking of both small-molecule (cumene) and large-molecule (1,3,5-tri-isopropylbenzene) hydrocarbons. The existence of mesopores may also make the acid sites easily accessible for reactants. Catalysts of W–Ni supported on Y/Al-SBA-15 and modified Y zeolites with mesopores were prepared by impregnation method, and the hydrocracking of heavy oil was performed on these catalysts. The catalyst using zeolite Y/mesoporous Al-SBA-15 composites as support gave higher yield of diesel compared to the catalysts using modified zeolite Y as support. In addition, the higher aromatics potential of heavy naphtha and the significantly lower BMCI (U.S. Bureau of Correlation Index) of tail oil revealed Y/Al-SBA-15 composite catalyst possessed integrated performance in the hydrocracking of heavy oil. These results proved that the combination of Y zeolites and mesoporous Al-SBA-15 plays a great role in improving the performance of catalysts for hydrocracking heavy oils.

Synthesis of EMT-rich faujasite in the presence of organic template of low-cost polyquaternium-6

EMT-rich faujasite zeolite has been successfully synthesized from an organic template of low-cost polyquaternium-6 in the absence of crown ether (18-crown-6). Additionally, low-cost water glass is used as a silica source taking the place of silica sol generally used in the conventional synthesis of EMT zeolite. X-ray diffraction (XRD) patterns show that the samples exhibit obvious peaks associated with EMT structure in addition to the peaks assigned to Y zeolite, indicating the presence of EMT and Y phase, and the purity of EMT zeolite reaches 70–80%. Scanning electron micrographs (SEM) show that partial crystals of the sample are typically hexagonal symmetry, confirming the presence of zeolite EMT crystals. Thermogravimetric and differential thermal analysis (TG-DTA) show that there are obvious peaks associated with combustion of organic template, suggesting that polyquaternium-6 plays an important role for the formation of zeolite EMT phase. Furthermore, temperature programmed desorption of ammonia (NH3-TPD) shows that the acidic amount of EMT-rich faujasite is slightly more than that of Y zeolite, and catalytic cracking of cumene shows that EMT-rich faujasite has higher activity than zeolite Y.

Chemical liquid deposition with polysiloxane of ZSM-5 and its effect on acidity and catalytic properties

ZSM-5 acidity was modified by chemical liquid deposition of silica (SiO 2-CLD), and the modification mechanism was investigated by pyrolysis gas chromatography-mass spectrometer (PGC-MS), absorbed pyridine infrared spectroscopy (Py-IR), temperature programmed desorption of ammonia (NH 3-TPD), thermal gravity analysis (TGA), X-ray diffraction (XRD) and physical adsorption and probe-molecule reactions. In SiO 2-CLD modification, the deposition process of polysiloxane modifier to silica over ZSM-5 is the acid-catalyzed degradation companying with the thermal pyrolysis, following oxidation at high temperature. Though the silanol hydroxyls of ZSM-5 disappear after the modification, most of the framework Al bridging hydroxyls and non-framework Al hydroxyls remain. Besides, the acidic amount of the modified ZSM-5 drops gradually with increasing extent of the modification, but the acidic strength distribution of the modified ZSM-5 is almost unchanged compared to parent ZSM-5. After the four-cycle modification, the conversion of 1,3,5-triisopropylbenzene (TIPB) in cracking over the modified ZSM-5 is reduced by 92%, so the external surface of the modified ZSM-5 may be regarded to be almost non-acidic due to coverage of deposition silica. Moreover, the modified ZSM-5 shows the high activity for cracking of cumene. High selectivity of para-xylene up to 96.2% is obtained in toluene disproportionation over the modified ZSM-5, compared to 24.3% selectivity of para-xylene over parent ZSM-5. Therefore, SiO 2-CLD with polysiloxane is an ideal modification for obtaining the high shape-selective ZSM-5 catalyst.

Influence of transition metals on the surface acidic properties of titania prepared by sol–gel route

A series of titania catalysts containing chromium, molybdenum as well as tungsten has been prepared by colloidal sol–gel route using metatitanic acid as the precursor. Structural characterization of the prepared catalysts was done with Energy dispersive X-ray analysis, X-ray diffraction, BET surface area and pore volume measurements. The influence of different transition metals like chromium, molybdenum and tungsten on the surface acidic properties of titania is investigated in detail. Two independent methods have been used to study the surface acidity of these catalyst systems: temperature programmed desorption of ammonia which is a measure of total acidity and thermodesorption studies using 2,6-dimethyl pyridine which is a measure of Bronsted acidity. Cumene cracking reaction is carried out over the prepared systems for further characterizing the acidity of the prepared catalysts. Remarkable enhancement in the surface acidity is observed after transition metal incorporation. The catalytic activity of the prepared catalysts was tested towards the dehydrogenation of cyclohexane.

Catalytic Activities of Platinum Supported on Silica-modified Alumina for Hydrodesulfurization of Thiophene

Hydrodesulfurization (HDS) of thiophene over silica-modified alumina-supported platinum (Pt/SiO2-Al2O3) catalysts was examined. The HDS activity of a Pt/Al2O3 catalyst was enhanced by silica modification. However, the optimal silica loading for HDS activity could not be identified. The dispersion of platinum on alumina, as measured by the hydrogen adsorption method, was enhanced by silica modification and the optimal silica loading for platinum dispersion was 10 to 40 wt%. The acidity of SiO2-Al2O3 was evaluated by 2-propanol dehydration (200°C) and cumene cracking (400°C). The optimal silica loading for the acidity of SiO2-Al2O3 was 90 wt%. Furthermore, the presence of Brönsted acid sites on SiO2-Al2O3 was confirmed by a pyridine adsorption method with FT-IR spectroscopy. The high HDS activity of the Pt/SiO2-Al2O3 catalyst is caused by both high Pt dispersion and formation of Brönsted acid sites.

Comparative study on the structural, acidic and catalytic properties of nano-sized and large-particulate mesoporous aluminosilicates

State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan, 030001, ChinaMesostructured aluminosilicate nanoparticles with wormhole-like framework structure were synthesized via sol–gel route at lowtemperature using cationic cetyltrimethylammonium bromide (CTAB) as template. Similar to hexagonal AlMCM-41, themesoporous nanoparticles had high surface area and uniform mesopores. It is more desirable that acid sites were generated directlyby calcining the as-synthesized nanoparticles, making a subsequent ion-exchange and calcination treatment superfluous. The acidstrength of acid sites on the present mesoporous nanoparticles was close to that on AlMCM-41 material, but less strong than thatof on microporous HZSM-5 crystals. Although highly acidic HZSM-5 was active for cumene cracking, the nanoparticles andAlMCM-41 were much more catalytically active in bulky 1,3,5-triisopropylbenzene cracking due to the facilitation of diffusion ofreactant/product molecules. More interestingly, the mesoporous Al substituted nanoparticles still exhibited excellent activities in1,3,5-triisopropylbenzene transformation after severe treatment by pure steam at 800 C for 2 h. In contrast, well-orderedAlMCM-41 totally lost its activity after the same treatment.KEY WORDS: sol–gel; mesostructured; nanoparticle; synthesis; catalysis.

Dehydroisomerization of butane into isobutene on Pt–Sn intermetallic compounds supported on H-SAPO-11

The dehydroisomerization of butane to form isobutene was carried out on Pt-based bimetallic catalysts supported on zeolite. Among various zeolites, Si-rich H-SAPO-11 was most appropriate for obtaining high selectivity to isobutene at higher butane conversions. The acid sites of Si-rich H-SAPO-11 were characterized by ammonia adsorption, 29Si MAS NMR, and the cracking of cumene. The addition of second elements, such as Sn, Pb, Zn and In, onto Pt/H-SAPO-11 retarded the hydrogenolysis activity of Pt, resulting in decreased methane selectivity. Among the second elements, tin was the most effective additive for obtaining higher isobutene selectivity. The formation of Pt–Sn intermetallic compounds, Pt 3Sn, PtSn, and PtSn 2, was revealed by XRD. The surface of Pt–Sn bimetallic particles was characterized through the dispersion of Pt and IR spectra of adsorbed CO. The formation of surface intermetallic compounds is proposed to retard hydrogenolysis by the ensemble effect.

Effect of aluminum modification on catalytic performance of Pt supported on MCM-41 for thiophene hydrodesulfurization

The catalytic activities and properties of platinum supported on siliceous MCM-41 and Al-modified MCM-41, such as Al-incorporated MCM-41 (AlMCM-41) and alumina-modified MCM-41 (Al 2O 3-MCM-41), for the hydrodesulfurization (HDS) of thiophene were investigated. Al 2O 3-MCM-41 was prepared by an impregnation method using aluminum nitrate (Al(NO 3) 3·9H 2O) aqueous solution. Pt/Al 2O 3-MCM-41 catalyst showed high and stable activity for HDS of thiophene and this activity was remarkably higher than that of a commercial CoMo/Al 2O 3 HDS catalyst. The catalysts were characterized by XRD, hydrogen adsorption, ammonia-TPD, 2-propanol dehydration, cumene cracking and FT-IR. Dispersion of platinum on Al 2O 3-MCM-41 was remarkably higher than on MCM-41 or on AlMCM-41. It was revealed that the acidity of Al 2O 3-MCM-41 was higher than that of MCM-41 or of AlMCM-41. Furthermore, it was observed that there exist Brønsted acid sites on Al-modified MCM-41. FT-IR spectra of thiophene adsorbed on Al-modified MCM-41 support indicates that thiophene molecules interact with Brønsted acid sites on Al-modified MCM-41. It was found that the HDS activity of Pt/quartz mixed mechanically with Al-modified MCM-41 catalyst was higher than that calculated. This suggests that there exists spillover hydrogen on supported Pt catalysts in the HDS of thiophene. Results revealed that the high activity of Pt/Al 2O 3-MCM-41 catalyst for HDS reaction is due to good harmony of high dispersion of Pt particles and Brønsted acidity of the support.

Role of surface pockets on MCM-49 structure in the alkylation of hydroquinone with tert-butanol

A series of MCM-49 catalysts with different Si/Al ratios were prepared and characterized by XRD, XRF, 27Al MAS NMR, BET, and SEM. The overall and external surface acidity of the catalysts were measured by temperature-programmed desorption of both small- and large-base probe molecules (NH 3 and 2,6-di- tert-butyl-pyridine), as well as by model acid-catalyzed reactions, such as cumene cracking and 1,3,5-tri- tert-butyl-benzene dealkylation, and compared with those of ZSM-5 and USY zeolites. The strong external acid sites on the surface pockets of MCM-49 play an important role in the alkylation of hydroquinone with tert-butanol. MCM-49 catalyst with a Si/Al ratio of 20 exhibits good activity and selectivity for the alkylation reaction, and it is more reusable than mesoporous molecular sieves such as AlSBA-15 and MSU-S (BEA) due to the higher thermal and hydrothermal stability of the crystalline zeolite framework.

Synthesis and characterization of acidic properties of Al-HMS materials of varying Si/Al ratios

HMS and Al-HMS materials with Si/Al ratio in the range 5–45 were synthesized by neutral templating pathway. The as synthesized as well as calcined samples were examined for pore size distribution, surface area and XRD. These investigations confirmed the hexagonal mesoporous structure formation at all Si/Al ratios. The TGA measurements indicated that two types of template species interacting with Si or Al could be distinguished. The acidity and acid strength distribution studies using microcalorimetric NH 3 adsorption indicated that the acidity increases with Al content in the mesoporous structure. The presence of Al in the structure creates a wide variety of acid sites of varying strengths. The heterogeneity of the sites also increases with Al content of the catalysts. The activities for cumene cracking reaction to test acidity of the materials supported the trend obtained from microcalorimetric NH 3 adsorption results.

Highly Acidic Mesostructured Aluminosilicates Assembled from Surfactant-Mediated Zeolite Hydrolysis Products

The surfactant-mediated hydrolysis of ZSM-5 zeolite affords five-membered ring subunits that can be readily incorporated into the framework walls of a hexagonal mesostructured aluminosilicate, denoted MSU-Z. The five-membered ring subunits, which are identifiable by infrared spectroscopy, impart unprecedented acidity to the mesostructure, as judged by cumene cracking activity at 300 degrees C. Most notably, MSU-Z aluminosilicate made through the base hydrolysis of ZSM-5 in the presence of cetyltrimethylammonium ions exhibits a cumene conversion of 73%, which is 6.7-fold higher than the conversion provided by a conventional MCM-41. This approach to stabilizing zeolitic subunits through surfactant-mediated hydrolysis of zeolites appears to be general. The hydrolysis of USY zeolite under analogous hydrolytic conditions also affords zeolitic fragments that boost the acidity of the mesostructure in comparison to equivalent compositions prepared from conventional aluminosilicate precursors.

新規シルセスキオキサンの合成と触媒機能

Preparation of novel oligosilsesquioxanes-based materials and metal-containing ones as homogeneous and heterogeneous catalysts of excellent activity are reviewed. The authors examined the activity of a V-containing silsesquioxane as a homogeneous catalyst for the photo-oxidation of simple alkanes. For the epoxidation of alkenes catalyzed by Ti-silsesquioxanes, the presence of alkenylsilyl substituents around the Ti center shows significant promotional effects. By utilizing silsesquioxanes bearing appropriate functional groups, novel caged molecules with organic-inorganic hybrid structures were prepared as well as soluble cooligomers, starburst-type polymers, and a dendrimer containing metallasilsesquioxanes. Furthermore, the authors found that these metal-containing silsesquioxanes can be good precursors of oxide catalysts with high BET surface areas and uniformly-controlled pores. Remarkably, the catalysts containing V and Al species were found to show excellent activity for photo-assisted aerobic oxidation of methane into methanal and the cracking of cumene, respectively.

Catalytic Performance of Noble Metals Supported on Alumina-modified Silica Gel for Hydrodesulfurization Reaction

The catalytic activities and properties of noble metals (Pt, Pd, Rh, Ru) supported on silica gel (SiO 2 ) and alumina-modified silica gel (Al 2 O 3 -SiO 2 ) were investigated for the hydrodesulfurization of thiophene. Al 2 O 3 -SiO 2 was prepared by an impregnation method using aluminum nitrate (Al(NO 3 ) 3 · 9H 2 O) aqueous solution. Pt/ 8 wt%Al 2 O 3 -SiO 2 catalyst showed the highest activity for hydrodesulfurization of thiophene among various supported noble metal catalysts and this activity was higher than that of commercial CoMo/Al 2 O 3 hydrodesulfurization catalyst. The sulfur tolerance of noble metal/SiO 2 was enhanced by Al 2 O 3 modification of SiO 2 and Pt/8 wt%Al 2 O 3 -SiO 2 catalyst showed the highest sulfur tolerance among the supported noble metal catalysts. Pt/ 8 wt%Al 2 O 3 -SiO 2 catalyst had high hydrogenating ability for unsaturated C 4 hydrocarbons formed in the hydrodesulfurization of thiophene. The catalysts were characterized by 2-propanol dehydration, cumene cracking, XRD, H 2 adsorption and FT-IR. Dispersion of Pt on 8 wt%Al 2 O 3 -SiO 2 was remarkably higher than that on SiO 2 and the particle size of Pt on 8 wt%Al 2 O 3 -SiO 2 was the lowest among the supported noble metal catalysts. The acidity of 8 wt%Al 2 O 3 -SiO 2 was higher than that of SiO 2 . Furthermore, Bronsted acid sites were present on 8 wt%Al 2 O 3 -SiO 2 . FT-IR spectroscopy of thiophene adsorbed on 8 wt%Al 2 O 3 -SiO 2 support indicated that the thiophene molecule interacts with the Bronsted acid site on 8 wt%Al 2 O 3 -SiO 2 . The activity of the double-layer (Pt/SiO 2 + 8 wt%Al 2 O 3 -SiO 2 ) catalyst obtained experimentally was higher than that calculated. This suggests that spillover hydrogen was present on Pt/Al 2 O 3 -SiO 2 in the hydrodesulfurization of thiophene. Both the Bronsted acid sites of Al 2 O 3 -SiO 2 and the Pt particles in the Pt/Al 2 O 3 -SiO 2 catalyst act as active sites for the hydrodesulfurization of thiophene.

Mesoporous materials with zeolite framework: remarkable effect of the hierarchical structure for retardation of catalyst deactivation

Hierarchical MFI zeolite was synthesized following a synthesis route using organic-inorganic hybrid surfactants; the resultant zeolite with mesoporous/microporous hierarchical structure exhibited remarkably high resistance to deactivation in catalytic activity of various reactions such as isomerization of 1,2,4-trimethylbenzene, cumene cracking, and esterification of benzyl alcohol with hexanoic acid, as compared with conventional MFI and mesoporous aluminosilicate MCM-41.