SAPO-34 Catalyst Research Articles

Controlling the SAPO-34 Particle Size to Enhance Reaction-Diffusion Behavior for Improving Catalytic Efficiency in the MTO Reaction

The SAPO-34 zeolite as an important catalyst is widely used in the methanol-to-olefin reaction, but understanding the internal diffusion behavior of its reactant methanol is still a challenge. In this work, a series of SAPO-34 catalysts with different particle sizes were prepared, among which the thin-layer SAPO-34 zeolite could be synthesized when the ratio of TEAOH/Mor is 8:1, which exhibits a high selectivity of 95% for light olefins and a long lifetime of 410 min. Through 29Si NMR and N2 physical adsorption–desorption, it indicates that more Si(4Al) coordination structures and a larger external volume jointly determine the stability of SAPO-34. Combining the TG and BET results of deactivated catalysts, it was found that the main reason for deactivation is the micropore blocked by coke deposition. The kinetic results demonstrated that the particle size of the zeolite is inversely proportional to its apparent reaction rate. The calculation of the Thiele modulus shows that the intramolecular diffusion rate of the small particle zeolite is faster. The catalytic efficiency can be enhanced by reducing the particle size due to the partly removed internal diffusion and the improved utilization of acid sites.

Effect of water and methanol concentration in the feed on the deactivation of In2O3-ZrO2/SAPO-34 catalyst in the conversion of CO2/CO to olefins by hydrogenation

On account of the superior performance of In2O3-ZrO2/SAPO-34 tandem catalyst in the direct synthesis of olefins from CO, CO2 and CO/CO2 mixture by hydrogenation, it is interesting to establish the conditions to avoid its deactivation due to the rapid coke deposition on SAPO-34. The co-feeding of H2O and/or methanol together with H2 + CO2/CO was studied in a packed bed reactor at: 400 °C, 30 bar; CO2/COx in the feed, 0–1; H2/COx in the feed, 1–3; and space time of 5 gcat h molC−1, quantifying the evolution with time on stream (up to 16 h) of CO2 and COx conversions and olefin, paraffin and CH4 yields. The effects of the co-feeding on coke content and its nature were determined by temperature programmed oxidation (TPO) analyses of the spent catalyst. The results highlighted the complex effect of the concentration of H2O and oxygenates (methanol/dimethyl ether (DME)) on the deactivation of SAPO-34 and on the products yields in the pseudo-steady state of the catalyst. Co-feeding H2O lessens coke deactivation, however, high H2O concentration leads to attenuate the acidity of SAPO-34, limiting the performance of the tandem catalyst (mainly in the CO2 conversion). Oxygenates co-feeding concentration limit value lies on its favoring effect for coke formation. In addition to this effect, the favorable attenuation of coke deactivation by the high H2 concentration (studied in runs with H2/COx ratio in the feed in the 1–3 range) plays a key role in the viability of the process, leading to a pseudo-steady catalyst state in which the activity is constant. The proven effect of H2O and methanol concentrations will be useful for establishing new catalysts and reaction conditions at which their presence in the reactor will attenuate deactivation.

Effect of Zr Modification on NH3-SCR Reaction Performance of Cu-Ce/SAPO-34 Catalysts

Molecular sieve catalysts containing transition metals have been attracting attention for their potential applications in various fields, including environmental and industrial catalysis. A Cu-Ce-Zr/SAPO-34 series of molecular sieve catalysts were prepared by the impregnation method, and the effect of Zr introduction on the selective catalytic reduction of NO by Cu-Ce/SAPO-34 molecular sieve catalysts was explored. Through various characterization methods, the physical and chemical properties of the catalysts were analyzed, and the denitration mechanism of the molecular sieve catalyst was discussed. This study found that the total acid content of the acid sites on the catalyst surface decreased with the introduction of Zr, leading to a decrease in the denitration efficiency of the catalyst. At 350–400 °C, the denitration efficiency of the 4Cu-4Ce-4Zr/SAPO-34 catalyst was over 80%, and at 400–500 °C, it was over 99%. Moreover, excessive metal Zr could destroy its CHA structure and decrease the denitration efficiency of the catalyst. This study analyzed the reaction mechanism of NH3-SCR of Zr-modified polymetallic zeolites and the effect of Zr modification on the NH3-SCR reaction results. This study contributes to the understanding of the performance of molecular sieve catalysts containing transition metals. Reliable conclusions were obtained, which offer data support for future research in the field of NH3-SCR.

Mathematical Model for the Industrial SMTO Reactor with a SAPO-34 Catalyst.

The methanol-to-olefins (MTO) technology creates a new non-oil route to produce light olefins. This paper reports a 14-lump MTO kinetic model for SAPO-34 catalyst, combined with the hydrodynamic model for the fast fluidized bed reactor of the industrial SMTO process. Selective deactivation is considered to quantify the product selectivity and abrupt catalytic activity change. Moreover, referring to the parallel compartment (PC) model, the activity difference between the circulating spent catalyst and the regenerated catalyst is considered. The validation results with the optimized kinetic parameters showed good agreement between the calculated value and the actual value. Sensitivity analysis of the industrial SMTO process was performed. According to the results, the established mathematical model can provide guidance for industrial production operations.

Industrial Regenerator Model for SMTO Technology.

In order to alleviate the current domestic oil shortage, China has studied the technology of using coal as the source to produce low carbon olefins, among which methanol to olefin (MTO) is an important process. Since the coke deposition of MTO catalyst is inevitable, the deactivated MTO catalysts need to be regenerated by continuous coke combustion to recover the activity. This paper used the actual industrial data to study the gas-solid two-phase fluidized bed of a SMTO regenerator and the coke combustion kinetics of the deactivated SAPO-34 catalyst, and established the mathematical model of the SMTO industrial regenerator. The kinetic parameters in the model were obtained and validated with different data, which showed that the model is reliable and can accurately predict the industrial reaction results and provide guidance for the SMTO production operation.

Ionothermal Crystallization of SAPO-11 Using Novel Pyridinium Ionic Liquid and Its Catalytic Activity in Esterification of Levulinic Acid into Ethyl Levulinate

A study using a novel pyridinium ionic liquid, namely 1-propylpyridinium bromide ([PPy]Br), to crystallize SAPO-11 under ionothermal conditions is reported. By carefully following the crystallization process, SAPO-11 can readily be crystallized in the presence of [PPy]Br, which serves as a synthesis solvent and structure-directing agent, at 150 °C after 133 h of heating. The study also focuses on manipulating other synthesis parameters (e.g., crystallization temperature, phosphorous content, silicon amount and [PPy]Br concentration) and investigating their respective effects on the formation of SAPO-11. The crystallized SAPO-11 has an acidic nature and a high surface area. Under conductive instant heating conditions, the SAPO-11 catalyst is very active in the conversion of levulinic acid into ethyl levulinate; 93.4% conversion and 100% selectivity of ethyl levulinate are recorded at 180 °C after 30 min of reaction. This result is comparable to or even better than those of conventional homogeneous catalysts.

From Lab to Technical CO2 Hydrogenation Catalysts: Understanding PdZn Decomposition.

The valorization of CO2 to produce high-value chemicals, such as methanol and hydrocarbons, represents key technology in the future net-zero society. Herein, we report further investigation of a PdZn/ZrO2 + SAPO-34 catalyst for conversion of CO2 and H2 into propane, already presented in a previous work. The focus of this contribution is on the scale up of this catalyst. In particular, we explored the effect of mixing (1:1 mass ratio) and shaping the two catalyst functions into tablets and extrudates using an alumina binder. Their catalytic performance was correlated with structural and spectroscopic characteristics using methods such as FT-IR and X-ray absorption spectroscopy. The two scaled-up bifunctional catalysts demonstrated worse performance than a 1:1 mass physical mixture of the two individual components. Indeed, we demonstrated that the preparation negatively affects the element distribution. The physical mixture is featured by the presence of a PdZn alloy, as demonstrated by our previous work on this sample and high hydrocarbon selectivity among products. For both tablets and extrudates, the characterization showed Zn migration to produce Zn aluminates from the alumina binder phase upon reduction. Moreover, the extrudates showed a remarkable higher amount of Zn aluminates before the activation rather than the tablets. Comparing tablets and extrudates with the physical mixture, no PdZn alloy was observed after activation and only the extrudates showed the presence of metallic Pd. Due to the Zn migration, SAPO-34 poisoning and subsequent deactivation of the catalyst could not be excluded. These findings corroborated the catalytic results: Zn aluminate formation and Pd0 separation could be responsible for the decrease of the catalytic activity of the extrudates, featured by high methane selectivity and unconverted methanol, while tablets displayed reduced methanol conversion to hydrocarbons mainly attributed to the partial deactivation of the SAPO-34.

A bifunctional Zn/ZrO2–SAPO-34 catalyst for the conversion of syngas to lower olefins induced by metal promoters

Syngas (CO/H2) was selected as a non-petroleum carbon source and transformed into lower olefins (C2–C4), aromatics (BTX), liquefied petroleum gas (LPG), and gasoline (C5–C11), respectively.

Hierarchical low-silica SAPO-34 with enhanced MTO performance: Mesopore template- and fluoride-free synthesis

The inherent mass transport limitations and undesired acidity of silicoaluminophosphate SAPO-34 catalysts are two key factors that result in a fast deactivation rate in the methanol-to-olefin (MTO) reaction. Herein, we demonstrate that SAPO-34 with hierarchical pore architecture and different silicon contents can be rationally synthesized by hydrothermal treatment of homogeneous amorphous silicoaluminophosphate precursors in the absence of mesopore templates and fluoride. It reveals that the hierarchical architecture is formed by in situ alkaline TEAOH etching of framework atoms. The silicon content (acidity) of the products can be facilely tuned in wide range. 29Si MAS NMR spectra reveal silicon mainly exists in the form of Si(4Al) in low-silica SAPO-34 catalysts free from silica islands. The hierarchical SAPO-34 catalyst with a moderate silicon content (nSi/n(Si + Al + P) = 0.048) and small particle size (265 ± 94 nm) exhibits a prolonged catalytic lifetime as well as a higher selectivity in MTO reaction, attributing to the synergetic effect of a fast diffusion speed and an appropriate acidic density.

A novel integrated process for selective preparation of jet-range fuels from low carbon alcohols and ABE

The development of effective route for the production of jet fuels from low carbon alcohols or ABE (acetone/butanol/ethanol) is of great significance for reducing carbon emission. The purpose of this work is to prove that jet fuels can be selectively produced from ABE and lower alcohols. This novel synthetic strategy was based on an integrated process: alcohols dehydration to light olefins over the SAPO-34 catalyst and olefin polymerization to jet fuels over the 2%Ni@5%Fe@Hβ catalyst. The comparison between the single bed reaction mode and double bed reaction mode, the active sites of the catalysts, and the reusability of the catalysts were investigated. The double bed reaction mode significantly improved the selectivity of jet fuels in the catalytic conversion of ABE and low carbon alcohols. High selectivity of jet-range fuels (80.1%) and high conversion of ABE (94.8%) were achieved by the integrated process.

A CO2 valorization plant to produce light hydrocarbons: Kinetic model, process design and life cycle assessment

Reliable Life Cycle Assessment (LCA) of processes for valorization of CO2-rich off-gas streams requires multidisciplinary contributions that span the development of active and selective catalysts, reactor design, plant modeling and optimization, as well as environmental impact analysis. Herein, we present the design and study of a CO2 valorization plant through methanol-mediated (tandem) hydrogenation to light hydrocarbons, with propane as the most abundant product. A state-of-the-art PdZn/ZrO2 + SAPO-34 catalyst combination was screened for catalytic activity and selectivity in a wide operation range. Optimal process conditions were found at 350 °C, 30–40 bar and co-feeding of CO2/CO. Kinetic parameters for the tandem reaction were extracted and used for the design of a multi-layer reactor, where the two catalysts are distributed according to: (i) CO2-to-methanol catalyst; (ii) mixed catalyst bed, and; (iii) methanol-to-hydrocarbons catalyst. This configuration outperformed the conventional dual bed and mixed bed reactor configurations in terms of process design. A Life Cycle Assessment of the plant suggested that a substantial decrease in the global warming impact of propane production will be highly driven by using green hydrogen from either solar or wind sources, although the comparison with fossil-derived propane indicated already a reasonable improvement even when using grey hydrogen from natural gas.

Directional Construction of Active Naphthalenic Species within SAPO-34 Crystals toward More Efficient Methanol-to-Olefin Conversion.

Olefin selectivity and catalyst lifetime are two key metrics for industrial methanol-to-olefin catalysts. Currently, it is very difficult to obtain high olefin selectivity and long catalyst lifetime at the same time. Herein, a feasible strategy combining precoking and steaming to directionally construct the active naphthalenic species within the crystal center of the SAPO-34 catalyst has been developed, which can not only promote the lower olefin selectivity to ∼89% (ethylene and propylene) but also prolong the catalyst lifetime by ∼3.7-fold in the methanol-to-olefin conversion. Structured illumination microscopy, in situ ultraviolet-visible spectroscopy, and online mass spectrometry elucidate the spatiotemporal distribution and evolution of the naphthalenic species during the precoking and steaming processes. This one-stone-two-birds strategy is applicable to a commercial SAPO-34 catalyst containing a binder, demonstrating its bright prospect in the methanol-to-olefin industry.

A highly efficient SAPO-34 catalyst for improving light olefins in methanol conversion: Insight into the role of hierarchical porosities and tailoring acid properties based on in situ NH3-poisoning

Hierarchical SAPO-34 zeolites with tunable porosity were hydrothermally synthesized by modulating the Si/Al molar ratios of the gel precursors, and the morphologies of SAPO-34 crystals gradually evolve from well-dispersed ultra-small nanocrystals to compactly polycrystalline aggregates, and to analogous polycrystallinites but adhered with minute amorphous debris by increasing the Si/Al ratio ranging from 0.20 to 0.67. The catalytic tests during methanol-to-olefins (MTO) reaction indicate that the Hier-SAPO-34-0.20 (Si/Al = 0.20) catalyst constructed by loosely nano-sized crystals centered at 50 nm presents prominent catalytic performances with about 2.5 times prolonged catalytic longevity and around 10 % improvement for the selectivity toward light olefins (ethylene and propylene) as compared to a reference catalyst. More interestingly, when Hier-SAPO-34-0.20 catalyst was in situ pretreated with NH3 flowing, the selectivity of light olefins can be greatly increased by 18.1 % at the initial stage and the corresponding even selectivity with time-on-stream can be elevated by 6.9 %. It founds that in situ NH3-poisoned catalysts with improved light olefins selectivity are also suitable for ZSM-5 zeolite. These results reveal that the weakened strong acid sites modified by NH3-poisoning play a pivotal role in suppressing the undesired hydrogen transfer reactions and thus giving a high selectivity for light olefins. This work highlights the importance of acidity fine-tailoring by in-situ NH3-poisoning strategy on hierarchical zeolites for the improvement of light olefin selectivity, which would be valuable guidance for industrial applications.

The Effects of SiO2/Al2O3 and H2O/Al2O3 Molar Ratios on SAPO-34 Catalyst in the Methanol to Olefin Process

Informed through synthesis and characterization of NH 3 TPD, BET techniques, the current study investigated the right contribution of silicon and water content on a 9 sample SAPO-34 catalyst with different molar ratios. The final prepared SAPO-34 catalytic performed reaction for the Methanol to olefin process was processed and reported at 410 0 C a reactor of fixed-bed. It was shown that catalysts with different SiO2 /Al2O3 and H2O/Al 2 O 3 ratios demonstrated high ethylene and propylene selectivity, due to their intensified crystallinity and size of crystals (1.3 to 1.7 μm). The highest degrees of ethylene and propylene selectivity for 3 samples were 50.25, 21.20, and 48.44, 19.16 respectively. Samples with ratios of different that possess high density and acute acidic sites to deactivate rapidly. The high density of acute acidic sites promoted the ultimate response to saturated hydrocarbons and aromatics based on olefins’ hydrogen transfer to and resulted in the coke generation on the top layer of the catalyst.

Synthesis of nano-sized small-crystal and hierarchical SAPO-11 molecular sieves and superior catalytic performance of their NiWS-supported catalysts in hydroisomerization of n-hexadecane

The nano-sized small-crystal and hierarchical SAPO-11 molecular sieves were successfully synthesized with l-Lysine as the crystal growth inhibitor, and their particle size reached 80 nm at the minimum, and the crystal size was 22.1 nm. With the synthesized SAPO-11 molecular sieve as support, the corresponding NiW supported catalyst was prepared for the hydroisomerization of n-hexadecane. The properties of small-crystal and hierarchical SAPO-11 molecular sieve and catalyst were analyzed by a series of physicochemical characterizations, and the formation mechanism of small-crystal and hierarchical SAPO-11 molecular sieve was proposed. The results showed that the reduction of crystal size greatly improved the BET specific surface area, mesopore volume of SAPO-11 molecular sieve. The decrease of crystal size increased the surface Si content of SAPO-11 molecular sieve, thus improving the surface acidity of SAPO-11 molecular sieve, and weakening the interaction between active metals and supports of the catalysts. In addition, the decrease of crystal size increased the dispersion and stacking number of the active phases, thus greatly improving the catalytic performance of the catalysts. Compared with the catalyst corresponding to the conventional SAPO-11 molecular sieve, the yield of i-hexadecane of the catalyst corresponding to small-crystal and hierarchical SAPO-11 molecular sieve increased by 45.34%.

Steering CO2 hydrogenation coupled with benzene alkylation toward ethylbenzene and propylbenzene using a dual-bed catalyst system

Utilization of CO2 as a C1 resource for the synthesis of aromatics is of great significance and is also related to carbon recycling. However, forming an ethylated or propylated side chain at the benzene ring by this strategy is difficult, and the products reported are methylated aromatics. Here, we show the first CO2 hydrogenation in tandem coupling with benzene alkylation to synthesize ethylbenzene and propylbenzene over a dual-bed system containing ZnZrOx, SAPO-34, and phosphorus-modified ZSM-5 catalysts. Controlled experiments and density functional theory studies reveal that the intermediate reactive species CHxO∗ (x = 1–3) of CO2 hydrogenation are preferentially alkylated with benzene to give methylated aromatics, rather than to form ethylated and propylated aromatics, when the three catalysts are simply mixed. By contrast, the three catalysts with rationally spatial distribution in the dual-bed system can afford 83.5% selectivity to ethylbenzene or 64.7% to propylbenzene in total aromatics without deactivation after 100 h.

SAPO-34 crystals with nanosheet morphology synthesized by pyrophosphoric acid as new phosphorus source

The nanosheet SAPO-34 zeolite crystals with a diameter of 300 nm and a thickness of 50 nm using a new phosphorus source (pyrophosphoric acid, H4P2O7) were synthesized. The roles of the pyrophosphate (P2O74−) species in the crystallization of SAPO-34 were elucidated. The results suggested that one P atom from the P2O74− species participated in the formation of the CHA framework structure while the other P atom served as a crystallization control agent, facilitating preferential crystal growth in [100] crystal plane. The SAPO-34 nanosheets have silica-rich shell and phosphorus-rich core leading to superior catalytic performance in methanol-to-olefin reaction (MTO). The catalytic lifetime of the SAPO-34 nanosheets was significantly improved due to the larger amount of medium-strong surface acidity and short diffusion pathway in comparison to the conventional SAPO-34 catalyst synthesized in the presence of the classical phosphorus source (H3PO4).

Investigation of Effective Parameters Ce and Zr in the Synthesis of H-ZSM-5 and SAPO-34 on the Production of Light Olefins from Naphtha

In this paper, Ce and Zr modified commercial SAPO-34 and H-ZSM-5 catalysts were synthesized via a wet impregnation method and used as catalysts for the production of light olefins from naphtha. The synthesized catalysts were characterized using SEM, TGA, XRD, BET, and NH3-TPD. Thermal catalytic cracking of parent catalysts (SAPO-34 and H-ZSM-5) and modified catalysts with Ce and Zr on the production of light olefins from naphtha has been studied. The effects of different loading of Ce (2–8 wt.%), Zr (2–5 wt.%), and different temperatures on the yield of ethylene and propylene were also investigated. The yield of ethylene and propylene improved by 21.78 wt% and 23.8 wt%, respectively, over 2% Ce and 2% Zr on SAPO-34 catalyst. This is due to the higher acid sites on the surface of modified catalysts. It was found that H-ZSM-5 with 2% Zr loading has the highest yield of light olefins (40.4%) at 650°C in comparison with unmodified parent catalysts, while Ce loading has less effect on the olefin yield compared to Zr loading. Finally, simultaneous loading of Ce and Zr showed no effect on the light olefin yield owing to the significant decline of acid sites.

Kinetic modeling of methanol-to-olefins process over SAPO-34 catalysts in a dual fluidized bed reactor–regenerator

Based on a lumped methanol-to-olefins (MTO) reaction kinetic model over SAPO-34 catalyst particles, a one-dimensional two-phase model was developed for bubbling fluidized bed reactor and catalyst regenerator. Comparison of the model predictions with literature experimental data showed good agreement over wide ranges of operating conditions both on a bench-scale unsteady-state bubbling fluidized bed reactor as well as pilot and demo-scale steady-state dual fluidized bed reactor–regenerator. The two-phase reactor model was also applied for catalyst coke content combustion with diluted air to design the regenerator of the dual fluidized bed reactor. Finally, the heat duty required for cooling circulating catalyst particles is obtained from overall energy balances. This integrated reactor–regenerator simulation allows for seamless analysis of MTO process. The trade-off between the complexity and applicability of the model makes it a useful choice for conceptual process designs, scale-up, integration with simulation software, optimization, process control and economic analyses.

Direct incorporating small amount of Ce (III) in Cu-SAPO-18 catalysts for enhanced low-temperature NH3-SCR activity: Influence on Cu distribution and Si coordination

The reduction of NOx emission during the cold start period of diesel vehicles requires special attention in accordance with the emission regulations. In this work, the direct incorporation of cerium and copper in SAPO-18 catalyst with AEI type framework structure (CuCe-SAPO-18) resulting in a substantial enhancement of the performance in the low-temperature NH3-SCR reaction (<200 ℃). A small amount of cerium (0.13–0.31 wt%) broadened the reaction temperature range of use and increased the hydrothermal stability of the catalyst considerably. The cerium species was introduced in the ion-exchange sites of Cu-SAPO-18 in the form of Ce3+ ions even with high loading (3.15 wt%). The Ce3+ ions were found to affect the distribution of silicon and aluminum atom coordination (29Si NMR, 27Al MAS NMR) in the AEI-type skeleton structure leading to an increase of both the amount of active Cu2+ species and the acidity of the CuCe-SAPO-18 catalysts that are beneficial for the NH3-SCR reaction.