Xumao Xiong

New insights into the support morphology-dependent ammonia synthesis activity of Ru/CeO2 catalysts

Three ceria nanocrystals with different morphologies (nanocubes, nanorods, and nanoparticles) were synthesized and used as supports to evaluate the support morphology-dependent ammonia synthesis activity in the structure-sensitive ammonia synthesis reaction. The Ru/r-CeO2 catalyst shows a higher catalytic reaction rate (3830 μmol g−1 h) than that of Ru/c-CeO2 (1289 μmol g−1 h) and Ru/p-CeO2 (529 μmol g−1 h) under the reaction conditions of 400 °C, 1 MPa, and 60 mL min−1. In addition, promoters (Cs, K, and Ba) can effectively enhance the catalytic activity of the catalysts such as 2Cs–Ru/r-CeO2 (14266 μmol g−1 h) and 2K–Ru/r-CeO2 (11227 μmol g−1 h). The effect of the morphology of the CeO2 support on the metal–support interaction and catalytic performance of the Ru/CeO2 catalysts can be correlated to the exposed crystal planes and surface composition/electronic structure of the CeO2 support with diverse morphologies.

Electronic metal–support interactions enhance the ammonia synthesis activity over ruthenium supported on Zr-modified CeO2 catalysts

Here we report that the electronic metal–support interaction influences the catalytic activity of ammonia synthesis. This effect produces an upwards shift of the d-band center of Ru nanoparticles. The upward shift of the d-band center of the Ru nanoparticles is considered to enhance the dissociation of the N2 molecule.

Effect of MgO/h-BN Composite Support on Catalytic Activity of Ba-Ru/MgO/h-BN for Ammonia Synthesis

A series of MgO/hexagonal boron nitride (h-BN) composite with different mass ratio were synthesized by impregnation method and used as supports for ruthenium catalysts in ammonia synthesis reaction. The catalysts were characterized by X-ray diffraction, N2 physical adsorption, X-ray fluorescent spectrometer, scanning electron microscope, transmission electron microscope, temperature programmed reduction of H2, and temperature programmed desorption of CO2 (CO2-TPD). The activity measurements of ammonia synthesis were carried out in a fixed-bed flow reactor with a mixture of N2 and H2 atmosphere under steady-state conditions (5.0 MPa, 350–500 °C, 5000 h−1). The results showed that the rate of ammonia formation was strongly influenced by the h-BN content used in the catalysts preparation process. The Ba-Ru[1:1] (molar ratio of Ba to Ru = 1:1)/MgO/h-BN[8:2] (weight ratio of MgO to h-BN = 8:2), Ba-Ru[1:1]/MgO/h-BN[6:4] and Ba-Ru[1:1]/MgO/h-BN[5:5] catalysts exhibited higher activity than Ba-promoted Ru/MgO catalyst. At 425 °C, 5.0 MPa, flow rate of 5000 h−1, and a N2/H2 = 1/3 atmosphere, the optimum activity of 506.9 ml/(gcat·h) was achieved when MgO/h-BN [8:2] was used as the catalytic support. The excellent activity was mainly attributed to the basicity of the MgO/h-BN combination-type support, especially “weak” and “medium” basic sites. Large numbers of basic sites were observed from CO2-TPD characterization due to the interaction between MgO and the h-BN material.

Preparation and Catalytic Properties of Barium Cerate and Yttrium-Doped Barium Cerate Supported Ruthenium for Ammonia Synthesis

Abstract Barium cerate (BaCeO3) and yttrium-doped barium cerate (BaCe0.9Y0.1O3-δ) were synthesized by the citric acid method and used as supports for Ru/BaCeO3 and Ru/BaCe0.9Y0.1O3-δ catalysts prepared by incipient wetness impregnation using Ru3(CO)12 as precursor. The supports and catalysts were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Their catalytic properties for ammonia synthesis were evaluated in a fixed-bed reactor. The stability of BaCeO3 was superior to that of BaCe0.9Y0.1O3-δ, and the catalytic activity of Ru/BaCe0.9Y0.1O3-δ was higher than that of Ru/BaCeO3. The rate of ammonia synthesis over Ru/BaCe0.9Y0.1O3-δ was 432.5 ml/(g·h) at 3.0 MPa, 425 °C, and 15 000 h−1, which was 1.6 times higher than that of Ru/BaCeO3. The electronic interaction between Ce4+ and Ru nanoparticles was the key factor for the difference in catalytic activity and stability.