SAPO-34 Samples Research Articles

Changing the Si distribution in SAPO-11 by synthesis with surfactants improves the hydroisomerization/dewaxing properties

The silicoaluminophosphates SAPO-11 isodewaxing catalysts were synthesized with varying Si content following conventional methods and using a route involving the presence of surfactant. Smaller crystal size (∼80 nm) and higher external surface areas were found for the samples prepared with surfactant. This synthesis route using surfactant gives SAPO-11 samples with greater numbers of stronger acid sites than those prepared by conventional synthesis. The Si 29 MAS-NMR spectra obtained for samples containing the same amount of silicon showed that SAPO-11 prepared with surfactant contains a higher relative concentration of Si ( nAl, 4- nSi), 0 < n < 4 , border environments, whereas large patches of Si(4Si) are predominant in the samples prepared without surfactant. These results support the idea that introducing surfactant during synthesis contributes to better Si dispersion, decreasing the size of Si(4Si) patches and increasing the number and strength of acid sites. The hydroconversion of n-hexadecane on Pt/SAPO-11 samples indicates that the samples synthesized with surfactant with similar Si content and very close crystallite size to those synthesized by conventional methods are much more active and selective for the hydroisomerization of long-chain n-paraffins.

Synthesis and characterization of SAPO-11 molecular sieves from alcoholic systems

SAPO-11 molecular sieves were synthesized from aqueous and nonaqueous systems by using different alcoholic solvents and their physicochemical properties were compared. The SAPO-11 samples synthesized from alcoholic systems had larger external surface area, higher Si contents and higher acidity than those of the sample synthesized from the aqueous system. Thereby, loaded with 0.5 wt.%Pt, the resulting Pt/SAPO-11 catalysts synthesized from alcoholic systems exhibited higher catalytic activities and selectivity for n-dodecane hydyroisomerization. Among the catalysts synthesized from alcoholic systems, the Pt/SAPO-11 catalyst synthesized from polybasic alcohol systems possessed the highest catalytic activities.

Hydroisomerization of Long-Chain Alkane Over Pt/SAPO-11 Catalysts Synthesized from Nonaqueous Media

SAPO-11 molecular sieves were synthesized from nonaqueous media. The effects of Si and Al sources as well as solvents on the catalytic performance of SAPO-11 were investigated by the hydroisomerization reaction of n-dodecane. The samples were characterized by XRD, XRF, N-2-adsorption, SEM, NH3-TPD, IR-NH3 and Si-29 CP MAS NMR. The SAPO-11 samples synthesized with tetraethoxysilane as the Si source showed higher Si incorporation contents than the SAPO molecular sieves prepared with polymeric Si sources (fumed silica and Si colloidal gel). The reaction results showed that Pt/SAPO-11 catalysts synthesized from ethylene glycol and glycerol media with the monomeric Si and Al sources (tetraethoxysilane, aluminum isopropoxide) exhibited higher catalytic activities than those catalysts with the polymeric Si or Al (pseudo-boehmite) sources, due to the larger external surface area and higher acidity of the former ones. Especially, the catalyst synthesized in an ethylene glycol medium possessed the highest catalytic activity. Over this catalyst, 88% conversion of n-dodecane was achieved at a low temperature of 250 degrees C.

High-silica SAPO-5 with preferred orientation: synthesis, characterization and catalytic applications

Silicon-rich SAPO-5 samples with preferred orientation were synthesized with a simple template of diethylamine at the crystallization temperature of 573 K and a short crystallization time. 29Si MAS NMR spectra showed that only SM2 occurred for the sample with Si/Al ratio of 0.25, while SM2 + SM3 occurred for the sample with Si/Al ratio of 0.42. Though there were very few strong acid sites in SAPO-5 framework with Si/Al ratio of 0.25, it showed high n-alkane hydrocracking activity. It also showed unusual catalytic behavior for longer chain hydrocarbons ( n-C12, n-C16), which could be adsorbed within SAPO-5 channels below 573 K, while hydrocracked at temperatures higher than 598 K. The 12-ring channels structure of SAPO-5 with preferred orientation is used to explain the unusual results.

Synthesis, physicochemical properties and hydroisomerization activity of SAPO-11 based catalysts

A series of silicoaluminophosphate (SAPO)-11 molecular sieve samples by using various raw materials and process parameters was prepared. Two of the selected SAPO structure materials were formed in extrudate supports, impregnated with platinum acid solution, thermally treated and tested in hydroisomerization process of so-called “cetane fraction” (mixture of n-C 13– n-C 20 hydrocarbons). It was found that the preferred parameters of SAPO-11 crystallization are: time, 20 h; temperature, 473 K, with use of n-propylamine as a pore shaping reagent. The obtained SAPO-11 samples were micro-porous materials, micropores consists of ca. 65% of total pore volume and 85% of total specific surface area. Application of Pt catalysts supported on SAPO-11 and alumina binder containing carrier (weight ratio 1:1) enabled hydroisomerization of cetane, n-paraffins fraction, with selectivity of 80–84%. At the low conversion levels the main product of isomerization were mono-branched paraffins while higher process temperature and the increase in conversion favoured obtaining of di- and poly-branched isomers.

Conversion of methanol to olefins over cobalt-, manganese- and nickel-incorporated SAPO-34 molecular sieves

Silicoaluminophosphate (SAPO)-34 molecular sieves modified with transition metals Co, Mn, and Ni were investigated for their activity, selectivity, and lifetime in the methanol to olefins (MTO) reaction and compared with that of unmodified SAPO-34. The electronic state and location of the metal ions in these materials were determined by magnetic measurements (temperature and magnetic field variations of magnetization). These magnetic studies show that for MnSAPO-34 and CoSAPO-34 metal ions are incorporated into the SAPO framework with concentrations ≃0.12 and 0.17 wt.%, respectively. Nickel modified SAPO-34 samples were prepared by two different procedures. For Ni-SAPO-34 prepared by one procedure ( Method I), the magnetic studies show the presence of nanoparticles (Ni or NiO) outside the SAPO framework. For NiSAPO-34 prepared by a second procedure ( Method II), these studies show that the nickel ions are incorporated into the SAPO framework. Although the total C 2–C 4 olefins activity on these materials was comparable to that of unmodified SAPO-34, significant variations in the deactivation behavior were observed among various metal-modified catalysts. MnSAPO-34 was found to be the best catalyst based on catalyst lifetime. In the case of Ni-SAPO-34 ( Method I), unusually high amounts of methane were observed in the products due to the presence of nanoparticles outside the SAPO framework.

Incorporation of Silicon into AlPO-5 Framework Sites: Higher Thermal Stability and Lower Extra-Framework Aluminum Concentration

Diffuse reflectance spectroscopy was used to investigate the structural modification of AlPO-5 microporous aluminophosphate synthesized in the presence of a silicon source and subjected to calcination in air. Extra-framework aluminium species, formed upon calcination and expulsion of aluminium from the framework, are detected by DRS because they are involved in aluminium-oxygen charge transfer transitions. Impregnation of the calcined AlPO-5 and SAPO-5 samples with ethanolic acetylacetone converted all the extra-framework aluminium atoms with distorted symmetry to a highly ordered symmetry, as evidenced by a distinct and well-defined 280 nm band in the DR spectra. The intensity of the 280 nm absorption band in AlPO-5 is much higher than those of all SAPO-5 samples with different silicon content. This is an indication of the presence ofa considerably higher amount of extra-framework aluminium in AlPO-5. Washing the acetylacetone treated samples with hot ethanol leads to extraction of some of the complexed aluminium. The progress of extraction could be monitored by both DR and UV-vis spectrophotometry.

Structure, acidity and catalytic properties of dealuminated SAPO-11 molecular sieves

A SAPO-11 molecular sieve was dealuminated in H 4EDTA solution to different Al content. Dealuminated samples were characterized by catalytic transformation of butene, o-xylene and cumene, IR analysis of adsorbed pyridine and 31 P -, 29 Si -MAS-NMR. Dealumination resulted in formation of strong Bronsted acid sites around Si domains. Amorphous AlPO 4 formed by deep dealumination of SAPO-11, led to a decrease of Bronsted acidity. The Lewis acidity was reduced by dealumination. The acidity of dealuminated SAPO-11 was measured and used to elucidate the catalytic properties. Butene isomerization was proceeded on Bronsted acid sites of medium strength. The selectivity of toluene disproportionation was favored on Lewis acid sites by low temperature and space velocity. Dealumination of SAPO-11 samples improved cumene cracking, especially at high temperatures. The reaction kinetics and mechanism were discussed.

Catalytic behavior in skeletal isomerization of linear butenes and acidic properties of ani-Pr2NH-templated sapo-11 molecular sieve

SAPO-11 samples were synthesized withi-Pr2NH as a novel template, and applied in catalytic skeletal isomerization of linear butenes. More linear butenes were converted with increasing Si content in SAPO-11 samples, while theiso-butene selectivity was proportional to the Si content only in the lower reaction temperature region. The maximum yield ofiso-butene was achieved around 763 K. The acidic properties of SAPO-11 samples were studied by NH3-TPD and IR spectroscopy. The strong acidity was due to the formation of Si domains in the framework lattice.

Sorption Properties of AlPO4-5 and SAPO-5 Zeolite-like Materials

We have studied by volumetric adsorption isotherm measurements the sorption properties of different AlPO4-5 or SAPO-5 samples, for sorbate species characterized by a large range of molecular size: D2, Kr, Ar, C2D2, CO2, CH4, CF4, and C(CH3)4. The highest sorption capacities, Qmax, greatly depend on the sorbate molecular size. A difference of 1 order of magnitude is observed between hydrogen and neopentane. In addition, we have found that the sorption capacities of the four analyzed AlPO4-5 or SAPO-5 samples vary by almost a factor of 2. This result clearly shows that, as a consequence of the one-dimensional character of the AFI micropore network, Qmax is very sensitive to small amounts of crystalline defects or impurities. For methane, Qmax is equal to 6 mol/uc, a quantity that is not compatible with the commonly accepted value of the internal diameter of the AlPO4-5 micropore diameter, ⌀M = 7.3 A. Moreover, an interesting phase transition phenomenon has been observed during the sorption of krypton and me...

A Study of the Feasibility of Incorporation of Chromium into the Molecular Sieve Framework: The Transformation of 1-Butene over Cr-Silicoaluminophosphate Molecular Sieves

The catalytic transformations of 1-butene were performed over a chromium-substituted silicoaluminophosphate molecular sieve (CrAPSO-11), over a Cr-supported SAPO-11 molecular sieve (Cr/SAPO-11), and over two SAPO-11 samples. For times-on-stream under 2.5 h, the CrAPSO-11 catalyst showed a higher skeletal isomerization efficiency (SIE) than the two prepared SAPO-11 samples and the supported chromium system. After 2.5 h a drastic decrease in the SIE occurred (for the CrAPSO-11 sample) with a concomitant increase in the formation of butadiene and 2-butenes. The formation of butadiene was considerably hindered over the supported system compared to that of the CrAPSO-11 sample. The cracking reactions as well as the formation of C5+ hydrocarbons were also suppressed over the supported system. The catalysts were recently characterized by XPS and redox cycles (12) and presently studied by XRD, DRS, and NO chemisorption followed by IR spectroscopy and acidity measurements performed with pyridine chemisorption. A larger amount of Cr(VI) was found by DRS and XPS (∼70%) for the oxidic CrAPSO-11 (O2, 773 K), compared to the supported system. For the latter, Cr(III) was the main species present. The NO chemisorption experiments showed the presence of high chromium oxidation states on the oxidic CrAPSO-11. After reduction (H2, 773 K), the distribution of oxidation states of chromium (XPS and NO chemisorption experiments) for the reduced CrAPSO-11 solid, was different ∼40% Cr(VI) and ∼60% Cr(III) compared to the oxidic sample. Cr(VI) showed a higher stability towards reduction in the CrAPSO-11 catalyst when compared to chromium supported on conventional supports. The distribution of oxidation states of chromium was very similar for the oxidic and the reduced Cr/SAPO-11 catalyst. The oxidic CrAPSO-11 catalyst showed an increase in the number of medium+strong acid sites compared to the other catalysts. The reduction process, however, decreased the Brønsted strong acid sites by a factor of two. A concomitant decrease was observed for the medium+strong Lewis acid sites, upon reduction. These results suggest that a partially unsaturated Cr(VI) in the vecinity of P–OH groups may act as strong Lewis sites, generating Brønsted acidity by Brønsted–Lewis interaction, as suggested in the literature. The supported sample showed a decrease of medium+strong Brønsted acid sites compared to the CrAPSO-11 solid. In this case, however, the reduction process did not cause major changes in the acidity distribution. The characterization as well as the catalytic data support and reinforce the model presented by Chen and Sheldon (J. Catal.153, 1 (1995)) for the related CrAPO-5 system. The results suggest the incorporation of chromium into the molecular sieve framework for the CrAPSO-11 catalyst.

Characterization of SAPO-11 synthesized conventionally and in the presence of fluoride ions

SAPO-11 samples have been synthesized by the conventional route and from an aqueous solution containing F– anions. Characterization of these samples by X-ray diffraction (XRD), chemical analysis, X-ray photoelectron spectroscopy (XPS), thermal analysis, NMR, adsorption measurements and catalytic test reaction reveals that the samples are highly crystalline, but differ in some physico-chemical properties. These differences in the properties of SAPO-11 obtained via different synthesis routes are correlated with different ordering of silicon substitution within the framework.

Dependence of the nature and catalytic performance on the synthesis factors of SAPO-5 molecular sieve

A series of SAPO-5 molecular sieves have been synthesized by varying the silicon source, template and crystallization time. X-ray diffraction (XRD), SEM-EDAX, IR and TPD of ammonia have been employed to characterize their structure and acidity. The results show that the type and the amount of the template has a great effect on the yield of SAPO-5. The silicon source also exerts influence on the morphology of SAPO-5 and its acidity. Prolonging the aging time not only increases the silicon content in SAPO-5, but also decomposes the large crystal into small one and alters the acidity. However, when the aging time is over 48 h, the crystallinity of the molecular sieve decreases and some SAPO-34 intergrows in the product. Brønsted acid sites with medium strength are predominant on the SAPO-5 samples prepared, with which the n-hexane cracking activity at 450°C runs parallel.

Cracking of n-hexane and n-butane over SAPO5, MgAPO5 and CoAPO5

The acid site distribution and the catalytic activity of SAPO5 MgAPO5 and CoAPO5 samples for cracking of light alkanes was studied. The acid strength of all samples was found to be similar to that of faujasites, that of CoAPO5 being somewhat weaker than that of the other samples. The catalytic activity for cracking of n-hexane and n-butane was nearly identical for most of the SAPO5 samples investigated. For n-hexane cracking, one of the SAPO5 samples also showed a significantly higher activity than the other SAPO5 samples. The catalytic activity was three times higher for CoAPO5 and MgAPO5. Their higher activity is not due to a higher strength of the acid sites, but was concluded to be caused by a higher contribution of the bimolecular cracking mechanism.

Synthesis and characterization of SAPO-5 molecular sieve using N,N-dimethylbenzylamine as template

The synthesis of SAPO-5 molecular sieves with high silicon contents has been attempted using N,N-dimethylbenzylamine as templating agent. SAPO-5 samples having silicon contents up to 35%, relative to total Si+Al+P, have been achieved. An increase in concentration of the templating agent in the synthesis gel effects increased silicon substitution albeit the formation of certain impurity phases. Characterization of such silicon-rich SAPO-5 materials has been carried out by various physiochemical techniques such as XRD, SEM, EDAX, MAS NMR, IR, TGA/DTA, TPD and a catalytic reaction, viz. the alkylation of toluene with methanol to xylenes.

Acidity and Catalytic Activity of MeAPSO-44 (Me = Co, Mn, Cr, Zn, Mg), SAPO-44, AIPO4-5, and AIPO4-14 Molecular Sieves in Methanol Dehydration

Abstract SAPO-44 and the isomorphously substituted MeAPSO-44 (Me = Co, Mn, Cr, Zn, Mg) molecular sieves have been synthesized. The temperature-programmed desorption (TPD) spectra and the reaction rates of methanol dehydration have been measured on these samples in comparison with AlPO4-5 and AlPO4-14 samples. The acidity strength of samples has been determined qualitatively from the temperatures of dimethylether desorption peaks, and the following sequence has been obtained: MnAPSO-44 > CoAPSO-44 ≍ ZnAPSO-44 > MgAPSO-44 > CrAPSO-44 > SAPO-44 ⪢ AlPO4-5 ≍ AlPO4-14. The following sequence of catalytic activity has been observed: AlPO4-14 > AlPO4-5 ≍ SAPO-44 > CoAPSO-44 > MnAPSO-44. The highest selectivity to ethene production among these catalysts has been found for CoAPSO-44. The selectivities to ethene of SAPO-44 and MeAPSO-44 (Me = Co, Mn, Cr) samples are about three times higher than the selectivities of SAPO-34 and MeAPSO-34 (Me = Co, Mn, Cr) samples. The selectivities of transition-metal-substituted MeAPSO-44 samples follow the Irving-Williams transition metal-ligand complex stability order.

Infrared study of cyclohexanol chemisorption in SAPO molecular sieves

The infrared spectra of cyclohexanol adsorbed on SAPO molecular sieves (four SAPO-5 samples with different SiO2 contents, SAPO-11 and SAPO-31 were studied) show bands due to cyclohexanone (1732 cm–1) at room temperature, while on heating cyclohexene is formed. The results are discussed in terms of the existence of basic sites parallel to the Brønsted acid sites.

Catalytic activity and Si, Al, P ordering in microporous silicoaluminophosphates of the SAPO-5, SAPO-11, and SAPO-37 type

The catalytic activity in the conversion of decane on SAPO-5, SAPO-11, and SAPO-37 samples with Si T-atom fractions ranging from 1 to 42% were determined. The relationship of catalytic activity with compositional parameters is discussed. Due to the nonuniform distribution of silicon, aluminium, and phosphorus over individual crystals, the overall chemical composition of a SAPO- n sample is unable to rationalize its catalytic activity. In order to explain the catalytic activity of SAPO-5, SAPO-1 l, or SAPO-37 materials, the contributions of aluminosilicate (SA) and silicoaluminophosphate (SAPO) crystal domains have been determined using 29Si MAS NMR. Acid sites located in the SA and SAPO domains and at their interphases contribute to the catalytic activity. The contribution of the different types of acid sites to the catalytic activity is strongly dependent on the SAPO- n structure type.

X-ray diffraction and solid-state n.m.r. studies of AEL molecular sieves: Effect of hydration

Interpretation of X-ray powder diffraction spectra by using profile refinement techniques allowed the determination of (i) the positions of P, Al and O atoms in AEL-type materials (AlPO 4-11, SAPO-11) and (ii) the effect of adsorbed water molecules on the geometry of the previously evacuated AEL framework. The as-synthesized sample (hereafter labeled SYN form) and the 550°C calcined form (CAL form) crystallize in the acentric Ima2 space group with 3P + 3Al sites per asymmetric unit, whereas the rehydrated material (WAT form) adopts the acentric Pna2 1 space group with 5P + 5Al sites per asymmetric unit. In MAS-n.m.r. spectroscopy, a broad 31 P peak observed for the SYN and the dehydrated CAL forms is centered near δ = −30.7 ppm and is interpreted as the evelope of three overlapping components with 2:1:2 intensity ratios (8P1:4P2:8P3). For the hydrated WAT form two peaks centered at δ = −23 and −29 ppm having an intensity ratio of 1:4 have been attributed to the 4P1 and the 4P2 + 4P3 + 4P4 + 4P5 sites, respectively. The first peak corresponds to the P1 species, which is attached to OH and/or water molecules, as shown by proton cross-polarization experiments. The second broad peak, which corresponds to the remaining P atoms, is interpreted as four overlapping peaks of equal intensity. Water molecules were shown by X-ray diffraction experiments to form dimeric clusters and to be located close to P1 in the elliptical channels. It is suggested that this atom could be substituted by Si atoms in the SAPO-11 samples, as supported by the observed 1:4 intensity ratio and by the fact that the intensity of the component corresponding to P1 decreases with increasing Si content.

ChemInform Abstract: Nature of Acid Sites in SAPO5 Molecular Sieves. Part 1. Effects of the Concentration of Incorporated Silicon.

AbstractThe properties of 3 SAPO5 samples containing decreasing concentration of amorphous material are characterized by IR spectroscopy, TPD, and SEM.