An in situ encapsulation process was used to prepare ordered worm-like mesoporous Pt@SAPO-11 catalysts with different Pt loadings. Transmission electron microscopy images showed that Pt nanoparticles encapsulated within the SAPO-11 support mesopores were uniformly distributed and highly dispersed and had a narrow particle size distribution of 2–7 nm. Scanning electron microscopy indicated that increasing the Pt loading from 0.6 to 1.6 wt % did not significantly change the crystalline morphology of the catalyst, although the crystallinity decreased slightly. The specific surface area and average pore diameter of the Pt@SAPO-11 were in the ranges of 72–116 m2/g and 8.1–9.5 nm, respectively, which are determined by the Brunauer–Emmett–Teller method and Barrett–Joyner–Halenda method, respectively. The NH3 thermal-programmed desorption established that increasing the Pt loading gradually decreased the total NH3 desorption and that a loading of 1.2 wt % produced the highest concentration of medium-strong acid sites (6.2 cm3/g STP). X-ray photoelectron spectroscopy and H2 temperature-programmed reduction showed that a Pt loading of 1.2 wt % gave the strongest interaction between Pt nanoparticles and the SAPO-11 support. The Pt@SAPO-11 catalysts were used for the preparation of C8–C17 alkanes by decarboxylation of oleic acid. Employing a reaction temperature of 340 °C, a CO2 atmosphere, a Pt loading on the catalyst of 1.2 wt %, and a reaction time of 4 h, 100% oleic acid conversion was obtained together with an 80% yield of C8–C17 alkanes.
A series of mesoporous Pt@SAPO-11 catalysts with different Pt loadings were prepared using an in situ encapsulation process. These materials exhibited good topological structures and high Brunauer–Emmett–Teller (BET) surface areas (132–166 m2 g−1). Transmission electron microscopy images showed that the Pt nanoparticles in this material were in the 5–8 nm size range and were highly dispersed on the inner surfaces of the SAPO-11 support. N2-BET analyses demonstrated that the samples had mesoporous structures with average pore sizes of 7.3–8.5 nm. Characterization of the 1.0 wt% Pt@SAPO-11 catalyst by X-ray photoelectron spectroscopy and H2-temperature programmed reduction indicated strong interactions between the Pt nanoparticles and the carrier. This material was used to promote oleic acid decarboxylation under CO2 and gave a C8–C17 alkane yield of 80.8% after 4 h at 340 °C. After five repeated uses, the catalyst still gave a yield of 77.6%.
This work employed dodecyl trimethyl ammonium bromide, sodium dodecyl benzene sulfonate (SDBS) or dodecyl dimethyl betaine (BS–12) along with a PEO–PPO–PEO (P123) block copolymer to obtain a dual template system for catalyst synthesis. Using Pt(NH 3 ) 4 (NO 3 ) 2 as the platinum source, a series of mesoporous Pt/SAPO–11 catalysts with different Pt loadings were prepared via an in situ synthesis and characterized by X-ray diffraction, specific surface area analysis, temperature programmed desorption, X-ray photoelectron spectroscopy and transmission electron microscopy. These catalysts each had a complete AEL model structure with pore diameters in the range of 8.1–10.9 nm and specific surface areas between 103 and 168 m 2 /g. At a Pt loading of 1.0 wt%, the Pt/SAPO–11–S synthesized with SDBS–P123 as the dual template showed the least Pt loss, the largest specific surface area (159 m 2 /g) and the smallest Pt particle size (6.1 nm). This material also exhibited the highest ratio of Pt metal to oxide, indicating that it contained more active metal sites. This catalyst was applied to the decarboxylation of oleic acid under CO 2 to prepare C8–C17 alkanes, the main component of biological aviation kerosene. At a reaction temperature of 340 °C and catalyst-to-oil mass ratio of 1:10, the yield of C8–C17 alkanes reached 80.6% after 6 h. This same catalyst provided a 73.8% yield after six reuses, demonstrating good stability.
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.
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