Pt-Cu bimetallic particles have been regarded as promising catalysts for propane dehydrogenation. The dispersion of Pt and Cu species on conventional supports always results in the formation of large Pt-Cu particles, and it is highly desirable to fabricate ultra-small Pt-Cu cluster catalysts for propane dehydrogenation. Herein, we used the isolated Cu species in the Cu-SSZ-13 to localize the Pt species and the alloying of Pt with Cu leads to a formation of ultra-small (<1 nm) Pt-Cu bimetallic clusters in the structure of SSZ-13. The structure of synthesized PtCu-SSZ-13 catalysts was studied by XRD, SEM, STEM, XPS, CO-FTIR, H 2 -TPR and EXAFS techniques, which demonstrates that Pt-Cu clusters are entrapped in the micropore of SSZ-13 and their migration can be greatly inhibited. The synthesized PtCu-SSZ-13 catalyst shows high activity and good regeneration in propane dehydrogenation. The optimized catalyst 0.3 %PtCu-SSZ-13 delivers propane conversion of 28.5 % (close to equilibrium conversion) with 100 % propane as feed under WHSV of 7.1 h −1 at 520°C, and its catalytic performance can be completely regenerated via calcination in air. Density functional theory (DFT) calculations indicate that the unique Pt-Cu bimetallic nanocluster structure reduces the energy potential for propane dehydrogenation as well as promotes the adsorption of C 3 H 8 and desorption of C 3 H 6 thus enhancing the activity of the PtCu-SSZ-13 catalyst.
Ye Ma,Shichao Han,Qinming Wu,Longfeng Zhu,Huimin Luan,Xiangju Meng,Feng-Shou Xiao
The metal-exchanged zeolites as catalysts have been widely applied in many catalytic reactions , but their syntheses are environmentally unfriendly due to the multiple steps such as ion-exchange for the formation of a large amount of wastes. Herein, we for the first time report a method for one-pot fabrication of metal-zeolite catalysts (M-SSZ-13, M-Beta, M-ZSM-5, and M-EU-1; M = Cu, Co, Ni) from a combination of solvent-free and sodium-free routes by mixing, grinding, and heating the raw materials of aluminosilicate gel, organic templates, and metal-amine complexes. As a typical example, Cu-SSZ-13 zeolite is successfully synthesized from heating the mixture of aluminosilicate gel, organic template, and Cu-amine complex. Catalytic tests in selective catalytic reduction of NO x with NH 3 (NH 3 -SCR) show that the synthesized Cu-SSZ-13 zeolite before and after hydrothermal aging at 750 °C for 16 h are completely comparable with the commercial Cu-SSZ-13 zeolite from the conventional hydrothermal synthesis. Very interestingly, the method in this work has obvious advantages such as high yield, reduced pollutants, and simple process, which should be potentially important for practical applications of the metal-zeolites in the future.
A crucial problem in membrane-based gas separation is to fabricate membranes with excellent permeability, selectivity, and stability. Here, a high-performance carbon molecular sieves membrane of TR-CMS/SSZ-13 was successfully produced by pyrolyzing a thermally rearranged (TR) mixed matrix membrane (MMM) that obtained from a copolyimide precursor (6FDA/ODA/6FAP(3:2)) and SSZ-13 zeolite as filler at 450 °C. The effect of SSZ-13 zeolite content and structures of precursors on the transport behavior of derived CMS membranes was thoroughly studied. After TR process, the as formed polybenzoxazole (PBO) chain resulted in an enhanced rigidity, higher fractional free volume (0.15 vs 0.17), and a significantly increased (1898 times) BET surface area. Further enhancing the treatment temperature to 650 °C, the formed TR-CMS membranes exhibited a huge improved BET surface area from 228.2 to 639.3 m 2 /g, delivering a remarkable gas separation performance with H 2 permeability of 7089 Barrer and H 2 /CH 4 selectivity of 136. When doping with SSZ-13 till 15 wt%, the TR-CMS/SSZ-13–15 % showed an even higher H 2 (9726 Barrer) and CO 2 permeability (6932 Barrer), as well as H 2 /CH 4 (150 vs 136) and CO 2 /CH 4 (107 vs 57) selectivity than the pure TR-CMS, which surpassed the newest 2019 Robeson Upper bound. This can associate with the strong interaction between the modified SSZ-13 and the polymer matrix that prevent the collapse of the aromatic strand during the pyrolysis process, thereby create more ultra-micropore volume and concentration. Conclusively, pyrolyzing TR-MMM precursor is an effective way to form high-performance membranes with good potential for CO 2 separation and H 2 purification.
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