SSZ-33 Zeolites Research Articles

Alkylation of phenols and acylation 2-methoxynaphthalene over SSZ-33, SSZ-35 and SSZ-42 zeolites

Zeolites with different framework topology (SSZ-33, SSZ-35 and SSZ-42) were investigated in alkylation of phenol, m-cresol and p-cresol, and acylation of 2-methoxynaphthalene. Their catalytic behavior was compared with commercial zeolites BEA, USY, MOR and ZSM-5. Borosilicates SSZ-33 and SSZ-42 were isomorphously substituted into aluminum form by low temperature hydrothermal treatment. The phenol conversions decreased in the order: BEA 91.9% ∼ SSZ-33 90.5% > MOR 58.0% > SSZ-35 38.0% > SSZ-42 22.6%. The selectivity to C-alkylated product 2-cyclohexylphenol prevailed over selectivity to 4-cyclohexylphenol and phenyl cyclohexyl ether almost for all tested catalysts. The selectivities to 2-cylcohexylphenol were as follows: SSZ-35 85% > BEA 67% > SSZ-33 42% > SSZ-42 35% (at conversion of cyclohexene = 20%). Zeolite SSZ-33 was quite effective catalyst in acylation of 2-methoxynaphthalene. The conversions of 2-methoxynaphthalene achieved over SSZ-33 zeolite were similar to that obtained over zeolite BEA. The selectivities to 2-acetyl-6-methoxynaphthalene achieved over zeolites BEA and SSZ-33 were in the range 48–63 % for both tested acylating agents.

Desilication of SSZ-33 zeolite – Post-synthesis modification of textural and acidic properties

Desilication conditions (concentration of NaOH, duration of the treatment) of SSZ-33 zeolite (CON topology) were investigated in respect to the textural and acidic properties of the obtained materials. As-synthesized borosilicate SSZ-33 was transformed by isomorphous substitution to Al-form. The alkaline treatment of Al-SSZ-33 zeolite resulted in the formation of mesopores and enhanced accessibility of Brønsted acid sites. The increase in the mesopore volume and also changes in the concentration of acid sites depends mainly on the concentration (pH) of the treatment. Simultaneously, the increase in the pH of the alkaline solution led to the slight increase in Brønsted acid sites and substantial decrease in the micropore volume more than 50%, in comparison with the parent material while the volume of mesopores increased significantly. All desilicated SSZ-33 zeolites are characterized by a broad mesopore-size distribution in the range of 5–20nm with the maximum depending both on the harshness and duration of the treatment. The average size of mesopores increases with increasing pH of NaOH solution.

Enhancing propylene production from catalytic cracking of Arabian Light VGO over novel zeolites as FCC catalyst additives

The catalytic cracking of vacuum gas oil over fluid catalytic cracking (FCC) catalyst containing novel additives was investigated to enhance propylene yield. A conventional ZSM-5, mesoporous ZSM-5 (Meso-Z), TNU-9 and SSZ-33 zeolite were tested as additives to a commercial equilibrium USY FCC catalyst (E-Cat). Their catalytic performance was assessed in a fixed-bed micro-activity test unit (MAT) at 520 °C and various catalyst/oil ratios. The cracking activity of all E-Cat/additives did not decrease by using these additives. The highest propylene yield of 12.2 wt.% was achieved over E-Cat/Meso-Z compared with 9.0 wt.% each over E-Cat/ZSM-5 and E-Cat/TNU-9, at similar gasoline yield penalty. The enhanced production of propylene over Meso-Z is attributed to its mesopores that suppressed secondary and hydrogen transfer reactions and offered easier transport and accessibility to active sites. The lower enhancement of propylene over the large-pore SSZ-33 additive was due to its high-hydrogen transfer activity. Gasoline quality was improved by the use of all additives, as octane rating increased by 7–12 numbers for all E-Cat/additives.

Acidic Properties of SSZ-33 and SSZ-35 Novel Zeolites: a Complex Infrared and MAS NMR Study

Two novel zeolites SSZ-33 and SSZ-35 were investigated with respect to their acidic properties using different probe molecules to characterize the accessibility and acid strength of Lewis and Brønsted acid sites. Ammonia, pyridine, pivalonitrile, and acetonitrile-d3 were used as probe molecules, and the results were correlated with 27Al and 1H magic angle spinning (MAS) NMR. Both SSZ-33 and SSZ-35 zeolites were found to possess bridging Si−OH−Al groups of virtually uniform and high acid strength. For both SSZ-33 and SSZ-35, there is the typical presence of highly disturbed OH groups (IR band around 3500 cm-1), which amounts to almost half of the overall Brønsted acidity. It was found that almost all bridging Si−OH−Al groups in SSZ-33 are located in the 12-MR rings. Both acetonitrile-d3 and pyridine sorptions suggest the presence of two types of Lewis sites in SSZ-35, differing in acid strength and electron-acceptor properties, whereas in the SSZ-33 zeolite only one type is present. The relative strength of these sites is higher than that of the Brønsted type for SSZ-35 and is of comparable strength for SSZ-33. 1H and 27Al MAS NMR measurements during thermal treatment allowed the assignment of NMR peaks to different surface OH species and the establishment of their relation to IR bands. NMR spectroscopy enabled the quantitative analysis of both free and hydrogen-bonded OH groups separately, showing that for both zeolites the amount of disturbed sites is higher than the number of free OH groups.

Quantitative nano-characterization of heterogeneous catalysts

Heterogeneous catalysts can be of varying complexity ranging from single or double phase systems to complicated mixtures of metals and oxides with additives to help promote chemical reactions, extend the life of the catalysts, prevent poisoning etc. Although catalysis occurs on the surface of most systems, detailed descriptions of the microstructure and chemistry of catalysts can be helpful for developing an understanding of the mechanism by which a catalyst facilitates a reaction. Recent years have seen continued development and improvement of various TEM, STEM and AEM techniques for yielding information on the structure and chemistry of catalysts on the nanometer scale. Here we review some quantitative approaches to catalyst characterization that have resulted from new developments in instrumentation.HREM has been used to examine structural features of catalysts often by employing profile imaging techniques to study atomic details on the surface. Digital recording techniques employing slow-scan CCD cameras have facilitated the use of low-dose imaging in zeolite structure analysis and electron crystallography. Fig. la shows a low-dose image from SSZ-33 zeolite revealing the presence of a stacking fault.

Inorganic factors in the synthesis of large-pore borosilicates from tricyclo [5.2.1.0 2,6] decane organo-cations

The synthesis of borosilicate zeolites was carried out using two stereoisomers of the N,N,N-trimethyl-8-tricyclo [5.2.1.0 2,6]decane ammonium cation. Each isomer produces two different zeolites as a function of boron concentration in the synthesis. All four zeolites produced are large pore (twelve-ring), consistent with the tendencies of this family of organo-cations to stabilize pores greater than 6 Å. Higher boron substitution favored multi-dimensional zeolites. Whether this is a result of substructure features needed to incorporate trivalent elements or a consequence of the potential amount of charge balancing needed for a pore-filling organo-cation is discussed. The syntheses were adversely affected by using sodium borate to increase boron concentration, with the phyllosilicate, Kenyaite, being produced instead. Keeping the sodium concentration sufficiently low and varying boron with boric acid allowed for successful crystallization of Beta or SSZ-33 zeolites, depending upon the organo-cation isomer. Beta zeolite was more efficient in incorporating boron into the structure.