ACS Catalysis
·
2022
·
IF 13.7
Danfeng Wu,Sixu Liu,Mingqi Zhong,Jiafei Zhao,Congcong Du,Yanling Yang,Yifei Sun,Jingdong Lin,Shaolong Wan,Shuai Wang,Jianyu Huang,Yali Yao,Zhe Li,Haifeng Xiong
Metal single-atom catalysts (SACs) have attracted extensive interest because of their maximum atom efficiency and potentially good performances. However, the understanding of the catalytic behavior and the stability of SACs in high-temperature catalytic reactions remains a major challenge, especially under reducing conditions. In this work, we investigated the nature and stability of Rh/CeO2 SACs with different Rh loadings (0.2–4 wt % Rh) during syngas conversion (260 °C, 2 MPa). Using CO-DRIFTS, we found that atomically dispersed Rh was dispersed on Rh/CeO2 catalysts with an Rh loading up to 3 wt %. The Rh/CeO2 catalysts were stable in H2 up to 350 °C, while Rh nanoclusters were formed in CO at 200 °C. During syngas conversion at 260 °C, the Rh single atoms (Rhiso) on a 0.5 wt % Rh/CeO2 SAC slowly agglomerated to form Rh nanoclusters (RhNC) and a Rhiso/RhNC ratio of ∼1:2.5 was obtained after ∼10 h time-on-stream run. Furthermore, the Rhiso/RhNC ratio did not change with further reaction, indicating that the reaction reached steady state after a 10 h run. After the catalysts reached steady state (∼10 h), the Rhiso/RhNC ratio on the spent Rh/CeO2 catalysts decreased with the increase in Rh loadings, while the reactivity increased first and then decreased. We observed an optimal value of Rhiso/RhNC ≈ 1:3 on the 1 wt % Rh/CeO2 catalyst, showing the maximum reaction rates of CO (rCO) and ethanol selectivity (SEtOH) of 85.8 μmol/s/gRh and 26.2%, respectively. This indicated that the combination of Rh single atoms and Rh nanoclusters is beneficial to the ethanol selectivity and reaction rate, which was confirmed by DFT simulations. Moreover, the ratios of Rhiso/RhNC on the spent catalysts under the steady state have good relationships with the CO conversion rate and product selectivity in the reaction.
研究领域:
催化化学
·
材料科学
✓ 已验证
DOI
高影响因子
CHINESE JOURNAL OF CATALYSIS
·
2024
·
IF 15.7
Shuyi Li,Changle Mu,Nianqiu He,Jie Xu,Yanping Zheng,Mingshu Chen
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.
研究领域:
催化化学
·
材料科学
✓ 已验证
DOI
高影响因子
NEW JOURNAL OF CHEMISTRY
·
2021
·Vol. 46
·期 3
·1158-1167
·
IF 3.591
Huan Fu,Huan Zhang,Guichun Yang,Jun Liu,Junyuan Xu,Peihuan Wang,Ning Zhao,Lihua Zhu,Bing Hui Chen
Catalysts of 0.54% (Pt, Rh, Pd or Ru)/Co(OH)2 and 1.23% Rh/Co(OH)2 were successfully synthesized via simple hydrothermal and precipitation methods for the selective hydrogenation of nitroarenes. It was found that 0.54% Rh/Co(OH)2 outperformed other catalysts, for example, 2-chloronitrobenzene hydrogenation (with a turnover frequency (TOF) of 575 h−1) under 3.0 MPa H2 at 100 °C for 1 h (much higher than that of 1.23% Rh/Co(OH)2; TOF, 398 h−1). Through characterization of the nanostructure (XRD, TEM, HRTEM, AC-STEM (spherical aberration-corrected scanning transmission electron microscopy), AC-STEM-EDX elemental mapping and line-scanning, H2-TPD, etc.), it was confirmed that Rh was dispersed in the form of single atoms and ultrasmall nanoclusters on Co(OH)2 for 0.54% Rh/Co(OH)2. Moreover, 0.54% Rh/Co(OH)2 also exhibited high selectivity for –NO2 hydrogenation for other selected nitroarene substrates hydrogenation reactions. This was mainly attributed to the presence of Rh as single atoms or super tiny nanoclusters in 0.54% Rh/Co(OH)2, leading to a significant increase in the number of active sites, beneficial adsorption of the –NO2-group at defect-rich Co(OH)2, and an interfacial synergy effect of Rh–Co(OH)2, thus improving the catalytic performance.
研究领域:
化学
·
催化材料科学
✓ 已验证
产品关联
DOI
高影响因子
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