ABSTRACT The surface structures of heterogeneous catalysts significantly impact catalytic performance, especially for structure-sensitive reactions. In this study, we employed surface techniques such as low-energy ion scattering spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy with CO as a probe (CO-FTIR) to investigate the surface dynamics of Rh/Al 2 O 3 catalysts for propane dehydrogenation (PDH). We observed a notable induction process for PDH on Rh/Al 2 O 3 catalysts, marked by significant variations in propane conversion, methane, and propylene selectivities. These changes were attributed to substantial coke formation. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy) and CO-FTIR revealed the coexistence of Rh nanoparticles , clusters, and single atoms on the surface. Through various dynamic quasi in-situ characterizations, we found that coke preferentially covered Rh clusters, thereby inhibiting C–C bond breaking and methane formation. Meanwhile, Rh single atoms were less affected by coke coverage and remained exposed as active and selective sites for PDH, favoring propylene production. This work underscores the sensitivity of PDH to the sizes of Rh species, with isolated Rh single atoms promoting propylene formation.
The hydrogenation of polycyclic aromatic hydrocarbons (PAHs) over highly efficient and stable catalysts to fine chemicals and intermediates for producing chemical materials is an effective approach to realize the high value-added utilization of coal tar and slurry oil. Herein, two kinds of Al2O3-supported Pt and Rh catalysts are synthesized by strong electrostatic adsorption (SEA) and used to catalyze the hydrogenation of anthracene. Compared with the traditional catalysts synthesized by wet impregnation, the Pt/Al2O3-SEA and Rh/Al2O3-SEA catalysts have smaller active metal particle sizes and higher dispersion, which can expose more active centers, showing higher catalytic activity. Interestingly, anthracene may be preferentially adsorbed on the surface of the Pt/Al2O3 catalyst in a parallel manner but on the surface of the Rh/Al2O3 catalyst in a lateral manner, which leads to the different hydrogenation routes. 9,10-Dihydroanthracene is an initial product for the hydrogenation of anthracene, which is rearranged into tetrahydroanthracene and subsequently hydrogenated to symmetrical octahydroanthracene (sym-OHA) over the Pt/Al2O3 catalyst. The high selectivity to sym-OHA (93%) with the conversion of anthracene near 100% can be achieved in the hydrogenation of anthracene at 240 °C and 7 MPa for 10 h. Additionally, due to the strong anchoring effect, the Pt/Al2O3-SEA catalyst shows high stability for six cycles. This work supplies a new tactic to develop high-performance catalysts for selective hydrogenation of PAHs to important monomers for synthesizing chemical materials.
Aluminium oxide (Al 2 O 3 ) is a promising catalyst support due to its excellent stability, high specific surface area, low price, and wide applicability. At present, most of the synthesis methods of Al 2 O 3 are wet chemical process, and the solid-state synthesis of catalysts is underdeveloped under solvent-free conditions. In this study, we proposed a novel strategy for solvent-free synthesis of Rh/Al 2 O 3 catalysts via mechanochemistry. The pore properties of the catalysts can be tuned by simply adjusting the amount of template CTAB and calcination temperatures. As a proof of concept, as-prepared catalysts are used to catalyze hydrolytic dehydrogenation of ammonia borane. The best catalyst Rh/Al 2 O 3 -CTAB(0.4)-500 achieves a total turnover frequency of 186.0 mol H2 ·mol Rh −1 ·min −1 at 298 K and the activation energy is 44.8 kJ·mol −1 . It also exhibits good cycling properties for catalyzing the hydrolysis of ammonia borane completely even after five runs. The catalysts were also characterized by various methods, including SEM, TEM, XPS, XRD, etc., to study the relationship between their structure and catalytic performance. The results show that the high activity of the catalyst is closely related to its large BET specific surface area and appropriate average pore size.
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