Ultra-fast synthesis of hierarchical SAPO-11 molecular sieves with the assistance of hydroxyl radicals

Considering the traditional time-consuming synthesis route and diffusion-limited micropore system of SAPO-11 (i.e., SAPO-11W), a hydroxyl radical assisted method has been developed to prepare hierarchical SAPO-11 within 5 min (i.e., SAPO-11M). Compared to previous reports, the unique contribution is to induce hydroxyl radicals by exposing carbon materials to microwave irradiation in an oxygen-containing atmosphere. Carbon materials play a dual role as mesopore filler and hydroxyl radical initiator. When employed to prepare deoxygenation catalysts for stearic acids, a higher selectivity for C15-C18 and isomers is observed due to the mild acidity of SAPO-11M. The Lewis-rich acidity of SAPO-11M exhibits an electron deficiency to interact with the hydroxyl oxygen atoms and promotes the hydrodeoxygenation of stearic acids with excellent atom economy. These results are important for opening up a new prospect of synthesizing SAPO molecular sieves (e.g., SAPO-11 and SAPO-5) by an efficient and facile route.

Toward n-Alkane Hydroisomerization Reactions: High-Performance Pt-Al2O3/SAPO-11 Single-Atom Catalysts with Nanoscale Separated Metal-Acid Centers and Ultralow Platinum Content

Long-chain n-alkane hydroisomerization reaction plays a vital role in petrochemical and coal chemical industries, which could produce high-quality hydrocarbon fuels and lubricant base oils for modern transportation and mechanical drive. However, minimizing precious metal usage while maintaining the catalyst performance remains a great challenge. Herein, a novel bifunctional catalyst toward n-alkane hydroisomerization reactions, Pt-Al₂O₃/SAPO-11 (Pt-A/S11) featuring nanoscale separated metal-acid active centers has been synthesized via a simple two-step procedure. In detail, Pt species was first loaded on the nanometer-sized alumina matrices through an incipient wetness impregnation method and then mixed with SAPO-11 molecular sieve to form the composite catalyst. Importantly, 0.015Pt-A/S11 catalyst with the ever-reported lowest Pt loading amount of 0.015 wt % exhibits an extraordinarily high isomer yield of 85.8% compared to previous published results and the traditional Pt-SAPO-11/Al₂O₃ (Pt-S11/A) catalyst accompanying with the direct contact between metal and acid sites (65.6%). It has been confirmed that the Pt species in 0.015Pt-A/S11 samples exist in single-atom form, leading to an excellent hydroisomerization performance. The possible reaction processes have been discussed to elucidate the exemplary catalytic performance of the synthesized Pt-A/S11 catalysts with nanoscale intimacy of metal-acid sites.

Pinpointing basic sites formed upon incorporation of iron in hierarchical SAPO-11 using catalytic model reactions

By utilizing previously established catalytic model reactions, a method for probing the topological location of transition metal sites incorporated in hierarchical silicoaluminophosphates (SAPOs) is presented. For the first time, iron(III)-incorporated hierarchical SAPO-11 (FeCTAB-11) was prepared and thoroughly characterized with conventional iron(III)-incorporated SAPO-11 (FeSAPO-11) as a reference. Initially, inductively coupled plasma - mass spectrometry (ICP-MS) indicated that the FeSAPOs contained similar amounts of metal (∼2.0 wt%), while N₂-physisorption confirmed the bimodal porosity of the hierarchical FeCTAB-11. Furthermore, X-ray absorption spectroscopy (XAS) revealed that iron(III) was isomorphously incorporated into both SAPO-11 samples, whereas CO₂-temperature programmed desorption (TPD) revealed the first reported presence of strong basic sites in the vicinity of a transition metal incorporated into a SAPO framework. The location of the basic sites, and thus the incorporated iron, was subsequently probed by studying the products of the base-catalyzed vapor phase isomerization of cyclohexanone oxime (Beckmann rearrangement, BMR) model reaction. Through an increased lifetime for the base-catalyzed production of aniline, the incorporated iron for FeCTAB-11 was found to be located in highly accessible mesopores, whereas the conventional FeSAPO-11 had incorporated iron located in its micropores. Lastly, the methanol-to-hydrocarbons (MTH) model reaction showed that both FeSAPOs only had Brønsted acid sites in the micropores of the structures. This was used to verify the pore connectivity of the hierarchical FeCTAB-11 by utilizing the base-catalyzed BMR mechanism's dependency on acid sites.

Hydroisomerization of n-Hexadecane Over Nickel-Modified SAPO-11 Molecular Sieve-Supported NiWS Catalysts: Effects of Modification Methods

The complexation-excessive impregnation modification method, which was original in this study, and the ion-exchange method and the in situ modification method were used to synthesize Ni-modified SAPO-11 molecular sieves. With the Ni-modified SAPO-11 samples as support, the corresponding NiWS-supported catalysts for the hydroisomerization of n-hexadecane were prepared. The effects of Ni-modification on SAPO-11 characteristics and the active phase were studied. The structure, morphology, and acidity of SAPO-11, as well as the interaction between active metals and support, the morphology, dispersibility, and stacking number of the active phase, were all changed by Ni-modification methods. The complexation-excessive impregnation modification method deleted a portion of Al from SAPO-11 molecular sieves while simultaneously integrating Ni into the skeletal structure of the surface layer of SAPO-11 molecular sieves, considerably enhancing the acidity of SAPO-11 molecular sieves. Furthermore, during dealumination, ethylenediaminetetraacetic acid generated more mesoporous structures and increased the mesoporous volume of SAPO-11 molecular sieves. Because the complexation-excessive impregnation modification method increased the amount of Ni in the surface framework of the SAPO-11 molecular sieve, it has weakened the interaction between the active phase and the support, improved the properties of the active phase, and greatly improved the hydroisomerization performance of NiW/NiSAPO-11. The yield of i-hexadecane of NiW/NiSAPO-11 increased by 39.3% when compared to NiW/NiSAPO-11. It presented a realistic approach for increasing the acidity of SAPO-11, reducing the interaction between active metals and support, and improving the active phase stacking problem.

Hydroisomerization of 1-octene utilizing hierarchical SAPO-11-supported Ni catalysts: effect of the alkyl chain length of the mesoporogen

The effects of the alkyl chain length of the mesoporogen on the physicochemical properties and 1-octene hydroisomerization of hierarchical SAPO-11 have been investigated.

Synthesis of Nickel In Situ Modified SAPO-11 Molecular Sieves and Hydroisomerization Performance of Their NiWS Supported Catalysts

SAPO-11 molecular sieves were modified with different Ni contents by the in situ modification method. The Ni-modified SAPO-11 molecular sieves were used as the supports to prepare the corresponding NiW-supported catalysts for the hydroisomerization of n-hexadecane. The Ni-modified SAPO-11 and the corresponding NiW-supported catalysts were characterized by X-ray diffraction, scanning electron microscopy, N₂ adsorption–desorption, NH₃-temperature-programmed desorption, pyridine adsorbed infrared, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The results showed that Ni in situ modification preserved the crystal structure of SAPO-11; increased the BET specific surface area, mesopore volume, and medium and strong Brønsted acid amount of SAPO-11; and increased the stacking number of the active phase of the catalysts. 3Ni-SAPO-11 possessed the largest BET specific surface area, mesopore volume, and medium and strong Brønsted acid amount. NiW/3Ni-SAPO-11 possessed the highest dispersion of the active phase and the highest sulfidation degree of the active metals. The results of the hydroisomerization of n-hexadecane showed that Ni in situ modification improved the catalytic activity and selectivity of the catalysts for the hydroisomerization of n-hexadecane to varying degrees. Especially, NiW/3Ni-SAPO-11 had the highest catalytic activity and isomer selectivity, and the maximum yield of isomeric hexadecane could reach 71.18%.

Probing the Design Rationale of a High-Performing Faujasitic Zeotype Engineered to have Hierarchical Porosity and Moderated Acidity

Porosity and acidity are influential properties in the rational design of solid-acid catalysts. Probing the physicochemical characteristics of an acidic zeotype framework at the molecular level can provide valuable insights in understanding intrinsic reaction pathways, for affording structure-activity relationships. Herein, we employ a variety of probe-based techniques (including positron annihilation lifetime spectroscopy (PALS), FTIR and solid-state NMR spectroscopy) to demonstrate how a hierarchical design strategy for a faujasitic (FAU) zeotype (synthesized for the first time, via a soft-templating approach, with high phase-purity) can be used to simultaneously modify the porosity and modulate the acidity for an industrially significant catalytic process (Beckmann rearrangement). Detailed characterization of hierarchically porous (HP) SAPO-37 reveals enhanced mass-transport characteristics and moderated acidity, which leads to superior catalytic performance and increased resistance to deactivation by coking, compared to its microporous counterpart, further vindicating the interplay between porosity and moderated acidity.

Synthesis of mesoporous silicate molecular sieves by the aerosol-assisted method for loading and release of drug

The mesoporous silicate molecular sieves were synthesized with polyether F127 as the template by the aerosol-assisted method for loading and release of ibuprofen (IBU). The synthesized samples were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and N2 adsorption-desorption isotherms. The drug IBU was applied as a model drug to investigate the drug release behaviour by ultraviolet spectrophotometry measurements. The investigation results demonstrate that mesoporous silicate molecular sieves by the aerosol-assisted method are spherical with a core-shell structure. As the drug carrier, it has good structural stability and can achieve drug controlled release which is expected. It exhibits safety to a certain degree. Therefore, the aerosol-assisted synthesis method provides a new idea for the synthesis of sustained-release drug carriers.

Effects of particle size on bifunctional Pt/SAPO-11 catalysts in the hydroisomerization of n-dodecane

SAPO-11 zeolites with different particle size are successfully synthesized by controlling the nucleation and the growth rate of the crystal.

Effect of Metal Precursors on the Performance of Pt/SAPO-11 Catalysts for n-Dodecane Hydroisomerization

Pt(NH₃)₄(NO₃)₂, Pt(NH₃)₄(Ac)₂, (NH₄)₂PtCl₄, and H₂PtCl₆ were used to prepare Pt/SAPO-11 catalysts to investigate the effect of Pt precursors on the hydroisomerization of n-dodecane. The catalyst derived from Pt(NH₃)₄(NO₃)₂ displays the best hydroisomerization activity and selectivity among these precursors. The hydroisomerization conversion of n-dodecane is affected by the platinum particle size, platinum dispersion, the location of platinum, and the valence state of platinum. The selectivity of n-dodecane is determined by the number of Brønsted acid sites and Pt crystal planes. These conclusions are verified by combining transmission electron microscopy, high-resolution transmission electron microscopy, hydrogen temperature programmed reduction, NH₃-temperature programmed desorption, and Py-IR studies. The catalyst prepared with Pt(NH₃)₄(NO₃)₂ as the precursor exhibits the smallest platinum particle size and the highest platinum dispersion. Most of the platinum particles are supported on the external surface of SAPO-11 with the Pt(111) crystal face. Such a catalyst also possesses a suitable number of Brønsted acid sites and then displays the best catalytic performance. Obviously, the use of various precursors for the Pt-based catalyst can significantly affect the performance of Pt/SAPO-11 for the hydroisomerization of n-dodecane.

Design and in situ synthesis of hierarchical SAPO-34@kaolin composites as catalysts for methanol to olefins

An in situ synthesis strategy to fabricate SAPO-34@kaolin composites from kaolin microspheres as catalysts for methanol to olefins is developed.

Bifunctional catalysts for the hydroisomerization of n-alkanes: the effects of metal–acid balance and textural structure

The summary of recent advances reveals excellent potentials for the preparation of novel bifunctional catalysts with excellent catalytic performances for n-alkane hydroisomerization.

New trends in tailoring active sites in zeolite-based catalysts

This review discusses approaches for tailoring active sites in extra-large pore, nanocrystalline, and hierarchical zeolites and their performance in emerging catalytic applications.

Synthesis and catalytic application of alumina@SAPO-11 composite via the in situ assembly of silicoaluminophosphate nanoclusters at an alumina substrate

An alumina@SAPO-11 composite with a core–shell structure has been synthesized via the in situ assembly and crystallization of silicoaluminophosphate nanoclusters.