SAPO-34 Samples Research Articles

Carbon nanotube templated synthesis of metal containing hierarchical SAPO-34 catalysts: Impact of the preparation method and metal avidities in the MTO reaction

Hierarchical SAPO-34 was synthesized hydrothermally using carbon nanotube as hard template and modified with Co and Ni by isomorphous substitution and impregnation methods. The prepared catalysts were characterized by XRD, SEM, TEM, XRF, UV–vis, NH3-TPD, H2-TPR, FTIR and N2 physisorption measurements and their catalytic performance was evaluated for transformation of methanol to light olefins (MTO). There were meaningful differences in terms of crystallinity, acidity, porosity and reducibility among the synthesized catalysts modified by impregnation and isomorphous substitution methods. In addition, the ethylene and propylene yields and the catalytic longevity were strongly dependent on Ni and Co avidities as well as on the modification procedure. The results indicated that compared to the unmodified hierarchical SAPO-34, the catalyst modified with Ni by means of isomorphous substitution improved the yield of ethylene while methane production was promoted over SAPO-34 impregnated with Ni. On the other hand, the Co-containing SAPO-34 samples enhanced the production of both ethylene and propylene relative to the unmodified mesostructured SAPO-34 and these modifications prolonged the catalyst lifetime. These changes in the catalytic behaviors could be ascribed to the changes in the acid sites and porous structure.

Carbon nanotube templated synthesis of hierarchical SAPO-34 catalysts with different structure directing agents for catalytic conversion of methanol to light olefins

Crystalline silicoaluminophosphate of the CHA framework type (SAPO-34) with a hierarchical pore structure was hydrothermally synthesized using carbon nanotube as the mesopore template and TEAOH and/or morpholine as structure directing agents. The synthesized samples were characterized by XRD, SEM, TEM, FTIR, NH3-TPD, XRF and N2-physisorption techniques and their catalytic performance was tested in MTO reaction. N2-adsorption results showed that the population of mesopores created inside the SAPO-34 crystals could be controlled by tuning the amount of carbon nanotube applied. It was also found that the structure directing agents could lead to significant effects in the crystallinity and mesoporosity of hierarchical SAPO-34 samples. Increasing molar ratio of TEAOH in the initial gel increased the mesoporosity of SAPO-34, but decreased its crystallinity and particle size. The hierarchical SAPO-34 samples showed superior catalytic performance in the MTO reaction with longer lifetime compared to the conventional SAPO-34. The hierarchical SAPO-34 prepared by the mixture of TEAOH and morpholine exhibited longer catalyst lifetime compared to those of other hierarchical SAPO-34 obtained by only TEAOH or morpholine. The characterization of the spent catalysts indicated that both rate of coke formation and coke-susceptibility of hierarchical SAPO-34 was lower than conventional SAPO-34.

Methanol conversion to light olefins over surfactant-modified nanosized SAPO-34

Ultrasonic and microwave-assisted aging processes were employed in the static hydrothermal synthesis of nanosized SAPO-34 molecular sieve. A series of nanosized hierarchical SAPO-34 samples with different degrees of mesoporosity were utilized to investigate the impacts of mesoporosity on the catalytic performance of the methanol to olefins (MTO) reaction. The so-called series were synthesized in the presence of various mesogenous templates, such as TPOAC, CTAB, and their combinations. These SAPO-34 samples were characterized by XRD, FE-SEM, BET, FT-IR and NH3-TPD techniques. The catalytic activities were studied in a fixed-bed reactor under atmospheric pressure, 450 °C and WHSV of 4 h−1. Comprehending the results, it can be said that in comparison with the typical catalysts, reliable MTO catalytic lifetime (420 min) as well as sufficiently high light olefins selectivity (90 %) was obtained through the nanosized hierarchical porous SAPO-34 templated with a mixture of 50 % CTAB and 50 % TPOAC. This achievement is associated to its effective combination of acidity and porosity.

High hydrothermal stability of Cu–SAPO-34 catalysts for the NH3-SCR of NOx

The effects of calcination temperature, Cu source and co-template contents on the activity and hydrothermal stability of Cu–SAPO-34 catalysts prepared by the one-pot hydrothermal synthesis method were investigated. Appropriate calcination temperature was important for the deNOx activity of Cu–SAPO-34 catalyst. The amount of Cu source and co-template in the resulting gel could impact the Cu loading and the crystallization of the final Cu–SAPO-34. Preferably, hydrothermal treatment of the Cu–SAPO-34 catalyst with Cu loading ca. 3.44% at 750°C for 16h increased the NH3-SCR activity slightly due to migration of CuO to isolated Cu2+ and the maintenance of the crystallinity as well as the acidity. Moreover, the catalyst aged at 800°C for 16h maintained >90% NOx conversion from 225 to 400°C, and the crystallinity, active Cu2+ species and acidity in Cu–SAPO-34 were not destroyed completely after such harsh treatment. Meanwhile, kinetic analysis over fresh and aged Cu–SAPO-34 samples were conducted and the conclusion were in agreement with the NH3-SCR tests, H2-TPR and NH3-TPD results.

Structural changes in SAPO-34 due to hydrothermal treatment. A NMR, XRD, and DRIFTS study

When SAPO-34 is used as an industrial MTO catalyst, structural transformations leading to permanent deactivation are inevitable. The performance loss is linked principally to a redistribution of Si in the material, leading to the formation of Si-islands/aggregates with a concomitant loss of Brønsted acidic sites and catalytic activity. In this work we have studied transformations taking place in a SAPO-34 sample after hydrothermal treatment by studying two samples with different levels of Si; 7 atomic % and 13 atomic % Si T-atoms, corresponding to about one and two Si per CHA cage respectively. The 13% Si sample contains significant amount of silicon islands in its as-synthesized form, while the 7% Si sample does not. The 7% Si sample was steamed for a week at 700 °C and a partial pressure of steam of 0.7 atm. The changes were analysed in the context of Si-island formation, and compared with the 13% Si sample. The results clearly illustrated existence of two distinct types of local aggregation of silicon: Silicon islands produced during synthesis and aggregate silicon reminiscent of silicon islands induced by hydrothermal treatment. The materials were synthesized with full 29Si isotopic enrichment and allowed us, for the first time, to characterise the multiplicity of silicon species in great detail by 29Si solid state NMR.

The effects of SiO2/Al2O3 and H2O/Al2O3 molar ratios on SAPO-34 catalysts in methanol to olefins (MTO) process using experimental design

To investigate the effects of silicon and water content on SAPO-34 catalyst, a number of experiments by using response surface methodology of molar ratios of SiO2/Al2O3=0.1–0.6 and H2O/Al2O3=50–120 were performed. The catalytic performances of prepared SAPO-34 samples at 410°C and 30wt.% methanol in water for MTO process were investigated. Due to relatively high crystallinity and small crystal size (1.3μm); SiO2/Al2O3=0.17 and H2O/Al2O3=109.75 catalyst showed high total light olefins selectivity (71.45%). ANOVA results indicated that the light olefins selectivity was influenced more by changing of SiO2/Al2O3 molar ratio rather of H2O/Al2O3 molar ratio.

Effect of Heteroatom Concentration in SSZ-13 on the Methanol-to-Olefins Reaction

SSZ-13 materials have been synthesized with varying amounts of Al to produce samples with different concentrations of Bronsted acid sites, and consequently, these SSZ-13 materials contain increasing numbers of paired Al heteroatoms with increasing Al content. These materials were then characterized and tested as catalysts for the methanol-to-olefins (MTO) reaction at 400 °C and 100% methanol conversion under atmospheric pressure. A SAPO-34 sample was also synthesized and tested for comparison. SSZ-13 materials exhibited significant differences in MTO reactivity as Si/Al ratios varied. Reduced Al content (higher Si/Al ratio) and, consequently, fewer paired Al sites led to more stable light olefin selectivities, with a reduced initial transient period, lower initial propane selectivities, and longer catalyst lifetime. To further support the importance of paired Al sites in the formation of propane during this initial transient period, a series of experiments was conducted wherein an H-SSZ-13 sample was exch...

The effect of iron loading and hydrothermal aging on one-pot synthesized Fe/SAPO-34 for ammonia SCR

The current commercially-available technique for NOx reduction for diesel engines is the selective catalytic reduction (SCR) of NOx with NH3 over Cu zeolites. One of the problems of this technique is their limited ability to convert NOx at diesel particulate filter (DPF) regeneration temperatures. In addition, during regeneration of the DPF there is a risk of thermally deactivating the SCR catalyst. Thus, the aim of the current work was the development of a catalytic system that can reduce NOx both at low as well as high temperature and in addition is stable at high temperature. In order to reach this goal, a Fe/SAPO-34 with chabazite (CHA) structure was combined in a system with a commercial Cu/CHA catalyst. Earlier studies have shown that it is difficult to ion-exchange Fe into CHA structures due to steric hindrance, and we have therefore used a novel synthesis procedure which incorporated iron directly into the zeolite structure. Fe/SAPO-34 with three different Fe-loadings (0.27; 0.47 and 1.03wt.% Fe) were synthesized and the catalysts were characterized using inductively coupled plasma atomic spectroscopy (ICP-AES), N2 adsorption–desorption isotherms, BET area measurements and X-ray diffraction (XRD). The chemical composition, porous and crystalline structure of the parent SAPO-34 sample were found to be only slightly affected by addition of small amounts of Fe in the framework zeolite structure. However, more visible changes in the crystallinity were observed in the Fe/SAPO-34 catalysts with higher Fe content, which were attributed to the unit cell size expansion provoked by integration of higher amounts of Fe into the zeolite SAPO-34 framework. The Fe/SAPO-34 with the lowest Fe-loading (0.27wt.%) was found to be the best catalyst when considering activity as well as high temperature stability. The synthesized Fe/SAPO-34 catalyst demonstrated a significantly improved NOx reduction performance at high temperatures (600–750°C) when compared to a commercial Cu/CHA SCR system, and the combined system (Fe/SAPO-34+Cu/CHA) exhibited a very good performance in a large temperature interval (200–800°C) that encompasses most diesel exhaust gas conditions.

Synthesis and characterisation of SAPO‐34 with high surface area

SAPO-34 molecular sieve with a high surface area has been successfully synthesised using Y5669 (N-[3-(trimethoxysilyl)propy]aniline) functionalised fumed, silica as the silica source and tetraethylammonium hydroxide as a structure directing agent via a 60-day crystallisation time. X-ray diffraction result indicates that the sample is highly crystalline SAPO-34 and the scanning electron (electron) microscopy images show that the sample is nanosized with a size of ca. 200 nm. N2 adsorption and ammonia temperature-programmed adsorption results indicate that the synthesised SAPO-34 sample exhibits a much higher microporous area and stronger acidity than the conventional SAPO-34. Moreover, the microporous surface area of the as-obtained SAPO-34 can reach 835 m2 g−1, which is difficult to realise using other synthesis methods.

Understanding the structure directing action of copper–polyamine complexes in the direct synthesis of Cu-SAPO-34 and Cu-SAPO-18 catalysts for the selective catalytic reduction of NO with NH3

Cu2+ cations complexed by linear polyamines have been studied as structure-directing agents (SDAs) for the direct synthesis of copper-containing microporous silicoaluminophosphate (SAPO) materials. The complexing ligands diethylenetriamine (DETA), N-(2-hydroxyethyl)ethylenediamine (HEEDA), triethylenetetramine (TETA), N,N′-bis(2-aminoethyl)-1,3-propanediamine (232), 1,2-bis(3-aminopropylamino)ethane (323), tetraethylenepentamine (TEPA) and pentaethylenehexamine (PEHA) have been investigated. For comparison, syntheses have been performed using the analogous nickel–polyamine complexes. Cu2+ and Ni2+ forms of both SAPO-18 and SAPO-34 materials have been prepared. While most polyamine complexes direct crystallisation to SAPO-34, SAPO-18 has been prepared with Cu2+(232), Ni2+(232) and Ni2+(TETA). The coordination geometry of the included metal complexes was studied by UV–visible and EPR spectroscopy and computer simulation. SAPO-18 is favoured by the smaller square planar complexes or octahedral species (with 2 water molecules) of 232 and TETA. Calcination leaves extra-framework Cu2+ and Ni2+ cations within SAPO-18 and SAPO-34 frameworks. In situ synchrotron IR spectroscopy of Ni-SAPO-18 has shown thermal template degradation occurs via nitrile intermediates. Rietveld structural analysis located extra-framework Cu2+ and Ni2+ cations released by calcination. In SAPO-34, Cu2+ and Ni2+ were located in the 8R window of the cha cage. A second site was found for Ni2+ at the centre of the six-membered rings (6Rs) of the double-six-ring (D6R) sub-units. In SAPO-18 both Cu2+ and Ni2+ cations were located only in the 6Rs of the D6R sub-units. Selected copper SAPO-18 and SAPO-34 samples were tested in the selective catalytic reduction of NO with ammonia (NH3-SCR); both showed high activity.

Synthesis and catalytic application of SAPO-5 by dry-gel conversion for the epoxidation of styrene with air

High silica content SAPO-5(d) with an AFI topology has been synthesized by dry-gel conversion (DGC) method. Various techniques have been used to characterize the structures of molecular sieves. XRD patterns show high crystallinity and purity of the DGC samples. XRF analyses prove high silica content of SAPO-5(d). The SAPO-5(d) has small particle size of 0.5–1 μm with large BET surface area. Co-SAPO-5-0.6(d) exhibits a high activity for the epoxidation of alkenes with air to achieve 94.5 mol% conversion of styrene and 87.2% selectivity of epoxide. Recycling studies and control experiments show the recyclable stability of Co-SAPO-5-0.6(d) as a heterogeneous catalyst. As a comparison, SAPO-5(h) samples by hydrothermal synthesis (HTS) method have also been prepared and applied in the epoxidation reaction. However, the catalytic activity of Co-SAPO-5-x(d) (82.2–94.5 mol%) is higher than that of Co-SAPO-5-x(h) (72.9–85.5 mol%), which can be correlated with high silica content, high cobalt content, small particle size and large surface area.

DTO 반응에서 촉매수명과 경질 올레핀 선택도에 미치는 SAPO-34의 산 처리 효과

Effects of the post-acid treatment of SAPO-34 sample by hydrochloric acid were investigated to enhance the catalytic performance in DTO reaction. Uniformly sized SAPO-34 samples with cubic-like morphology were prepared by hydrothermal method using TEAOH and DEA as the structure directing agents. It was modified in terms of the HCl concentration and treating time. As a result, the total surface area and micropore volume for the well modified samples increased and the total acid site was somewhat decreased along with the erosion of the external surface. Especially, the catalytic lifetime and light olefins selectivity for acid treated SAPO-0.2 M (3 h) samples were considerably enhanced compared with those of untreated SAPO-34 samples. It indicates that the deactivation by coke formation proceeds mainly at the pore entrance on the external surface. Therefore, the acid treatment was confirmed to be a simple method which can significantly improve the catalytic performance by modifying the external surface of SAPO-34 catalyst.

Synthesis of SAPO-34 with the presence of additives and their catalytic performance in the transformation of chloromethane to olefins

SAPO-34 molecular sieves were synthesized in the presence of soluble starch, sodium dodecyl sulfate and cetyltrimethylammonium bromide as the additives under hydrothermal conditions, and the differences stemmed from the additives among all obtained SAPO-34 samples were characterized by XRD, SEM, BET, NH3-TPD and TG. Compared with the conventional SAPO-34 sample, the SAPO-34 samples modified by sodium dodecyl sulfate and cetyltrimethylammonium bromide showed less crystalline order, enlarged mesopore volume and external surface area and a reduction in total acidity amounts. Meanwhile, the SAPO-34 modified by soluble starch exhibited more total acidity amounts than the conventional SAPO-34 samples. The SAPO-34 samples modified by sodium dodecyl sulfate and cetyltrimethylammonium bromide showed better catalytic stability and less carbon deposition than the conventional SAPO-34 catalyst in the conversion of chloromethane to olefins due to the reduction in total acid sites and the increasing mesopore volume. The overall results of this study demonstrate that it is an effective way to modify the SAPO-34 molecular sieve with sodium dodecyl sulfate and cetyltrimethylammonium bromide as the additives for improving the SAPO-34 catalyst stability in the transformation of chloromethane to olefins.

Cooperative effects of secondary mesoporosity and acid site location in Pt/SAPO-11 on n-dodecane hydroisomerization selectivity

Two different methods, organosilane templating and carbon templating, were used to generate secondary mesoporosity within SAPO-11. The former method produced mesoporous SAPO-11 samples with a large amount of external acidity, while the latter produced mesoporous samples containing predominantly internal acid sites. It was shown that, depending on the location of Brønsted acid sites, Pt supported on mesoporous SAPO-11 samples can exhibit widely ranging maximum isomerization yields from 13% to 84%, while solely microporous SAPO-11 showed 44% isomerization yield. The results indicate that the presence of secondary mesoporosity can be either remarkably beneficial or detrimental to hydroisomerization selectivity depending on the spatial location of the acid sites. The present results clearly showed that hydroisomerization selectivity of the catalysts can be significantly enhanced by facilitating the hydrocarbon diffusion via the formation of secondary mesopores while suppressing the formation of external acid sites that can non-selectively catalyze consecutive cracking reactions.

Modeling of SAPO-18/34 intergrowth crystal structure

"Aluminophosphate framework structures have been widely studied because of their many technological applications. The most significant application of aluminophosphate type framework catalysts is in the methanol-to-olefin (MTO) conversion process [1], catalysed by SAPO-34 (the silicoaluminophosphate form of the chabazite (CHA) zeolite framework with silicon substituted into its structure). The effectiveness of SAPO-34 in the MTO process is due to both the shape selective properties of the framework and the concentration and strengths of the acid sites created by silicon substitution [2]. Another aluminophosphate framework MTO catalyst is SAPO-18 (zeolite framework type (AEI)), which has a very closely related structure to SAPO-34 and can form intergrowths with it. It has been suggested that the level of intergrowth can affect the efficiency of the MTO process [3], however, assessment of the level of intergrowth has remained difficult. We present a consistent model of the crystal structure of SAPO-18/34 family members which can accurately determine the level of intergrowth. The model utilises two types of stacking fault: Displacement and Growth which have significantly different effects on the diffraction pattern. A series of powder diffraction patterns is calculated using the Discus software package. Changes in the level of intergrowth and stacking fault type strongly affect the calculated pattern. A series of patterns has been calculated to illustrate this. The structure of an intergrown SAPO-34 sample with 4.8% Si content is modelled and refined using Displacement stacking faults. An example of ""defect-free"" AlPO-18 (0% Si content) is then presented. Refinement of the model shows that even this contains a small amount of stacking faults. Finally, a simple method for defect level estimation is proposed based on FWHM (Full Width at Half Maximum) ratios for selected Bragg reflections."

The Synthesis of Hierarchical SAPO-34 and its Enhanced Catalytic Performance in Chloromethane Conversion to Light Olefins

Hierarchical SAPO-34 molecular sieve was successfully synthesized by hydrothermal crystallization method with cetyltrimethyl ammonium bromide as mesoporous generating agent. The influence of different addition amounts of CTAB on the crystalline structures, morphology features, textural properties and acidity of hierarchical SAPO-34 catalysts were characterized by XRD, SEM, BET and NH3-TPD techniques. The results exhibit that the crystal size, mesoporous structure and the total acid amounts of hierarchical SAPO-34 are affected greatly by the molar ratio of CTAB/Al2O3. The selectivity of light olefins (ethane and propylene) can achieve 80 % for all SAPO-34 samples tested in the conversion of chloromethane to light olefins. Compared with the conventional SAPO-34, the hierarchical SAPO-34 samples show better catalytic stability and less carbon deposit in this conversion due to the reduction in total acid sites and the increasing mesopore volume.

Intergrowth structure modelling in silicoaluminophosphate SAPO-18/34 family

We present a consistent model of the crystal structure of SAPO-18/34 family members. The model utilises two types of stacking fault: Displacement and Growth which have significantly different effects on the diffraction pattern. A series of powder diffraction patterns is calculated using the Discus software package. Changes in the level of intergrowth and stacking fault type strongly affect the calculated pattern. A series of patterns has been calculated to illustrate this. The structure of an intergrown SAPO-34 sample with 4.8% Si content is modelled and refined using Displacement stacking faults. An example of “defect-free” AlPO-18 (0% Si content member of SAPO-18/34 family) is then presented. Refinement of the model shows that even this contains a small amount of stacking faults. Finally, a simple method for defect level estimation is proposed based on FWHM ratios for selected Bragg reflections.

Morphology control of SAPO-34 by microwave synthesis and their performance in the methanol to olefins reaction

SAPO-34 molecular sieves with different crystal morphologies were synthesized under microwave conditions. The type of organic templates, crystallization time and temperature were optimized to control the synthesis. These SAPO-34 samples were characterized by XRD, SEM, EDX, TG, nitrogen adsorption–desorption, NH3-TPD and solid state MAS NMR techniques. It was found that the crystallization conditions greatly affected the crystal morphology, textural data, Si incorporation and acidity of SAPO-34. Pure SAPO-34 with uniform sphere particles of 20 nm was obtained after crystallization at 165 °C for 0.75 h under microwave conditions using TEAOH as the template. Raising the temperature to 220 °C and prolonging the crystallization time to 2 h led to the formation of nano sheet-like SAPO-34 with a BET surface area of 593 m2/g. NH3-TPD profiles showed that low crystallization temperature and short crystallization time resulted in fewer weak acid sites and strong acid sites, while higher crystallization temperature and longer crystallization time increased the amount of both acid sites, which may benefit the methanol to olefins (MTO) reaction. The nano sheet-like SAPO-34 exhibited 100 % methanol conversion for 380 min during the MTO process, an ethylene selectivity of 51.77 % and a C2=–C4= selectivity of 90.20 %. The result was much better than that of the sample with a larger cubic morphology of 1.5–2.5 μm synthesized under hydrothermal conditions, on which the 100 % methanol conversion could only be kept for 212 min as well as an ethylene selectivity of 49.84 % and a C2=–C4= selectivity of 86.81 %. The unique morphology of the nano sheet-like SAPO-34 decreased its coke formation rate, which might be responsible for its improved catalytic performance.

Synthesis and Evaluation of Cu-SAPO-34 Catalysts for Ammonia Selective Catalytic Reduction. 1. Aqueous Solution Ion Exchange

SAPO-34 molecular sieves are synthesized using various structure directing agents (SDAs). Cu-SAPO-34 catalysts are prepared via aqueous solution ion exchange (IE). Catalysts are characterized with surface area/pore volume measurements, temperature programmed reduction (TPR), electron paramagnetic resonance (EPR), and nuclear magnetic resonance (NMR) spectroscopies. Catalytic properties are examined using standard ammonia selective catalytic reduction (NH3–SCR) and ammonia oxidation reactions. During solution IE, different SAPO-34 samples undergo different extent of structural damage via irreversible hydrolysis. Si content within the samples (i.e., Al–O–Si bond density) and framework stress are key factors that affect irreversible hydrolysis. Even using very dilute Cu acetate solutions, it is not possible to generate Cu-SAPO-34 samples with only isolated Cu2+ ions. Small amounts of CuOx species always coexist with isolated Cu2+ ions. Highly active and selective Cu-SAPO-34 catalysts for NH3-SCR are readily ...

Alkylation of naphthalene with methanol over SAPO-11 molecular sieve synthesized by different crystallization methods

Silicoaluminophosphate SAPO-11 molecular sieves were synthesized by both traditional hydrothermal and microwave irradiation methods. Their properties were characterized by multiple physico-chemical methods and compared in the alkylation of naphthalene with methanol. The results obtained indicate that the different preparation methods result in differences in the characteristics of the prepared samples. Compared to SAPO-11 obtained by the traditional hydrothermal method, samples synthesized by microwave irradiation possessed a lower content of silica, larger dimensions of both the individual crystals and polycrystalline agglomerates, and a lower amount of strong Brönsted and Lewis acid sites. Investigation of the properties of the prepared SAPO-11 materials in a naphthalene methylation reaction revealed that all of the samples demonstrated good activity in the reaction and catalytic stability with Time-On-Stream regardless of the synthesis method used. A higher 2,6-dimethylnaphthalene/2,7-dimethylnaphthalene molar ratio was observed for SAPO-11 samples prepared by microwave irradiation, which was attributed to a milder acidity of these materials.