A bimetallic catalyst 4.6%Cu–1.0%Ru/HZSM-5 was found efficient in the conversion of acrolein and ammonia to 3-picoline in the presence of hydrogen as carrier gas. Hydrogen as a carrier gas enhanced the selectivity of 3-picoline and the total carbon yield of pyridines. TEM and XPS characterization revealed that copper and ruthenium are present in the forms of CuO and RuO2 species and reduced in situ to Cu0 and Ru0 in catalytic run, respectively. The two metal species are precisely located in the identical area and close to each other, allowing synergistic effect between the two metals in the hydrogenation or dehydrogenation elementary step in the reaction, also leading to high yield of 3-picoline and total carbon yield of pyridine bases. Besides, the good performance of 4.6%Cu–1.0%Ru/HZSM-5 compared to the other tested Cu–Ru bimetallic catalysts was derived from the comprehensive results of its surface area and hydrogenation or dehydrogenation activity. The characterization results of TEM, EDX, XPS, pyridine adsorption IR spectra, TG-DSC, and N2 adsorption–desorption analysis revealed that the catalyst deactivation was owing to the deposition of carbonaceous substances on the active sites of the catalyst during the catalytic reaction. The deposited carbonaceous substances could be removed by calcination in air at 550 °C, and the activity of the 4.6%Cu–1.0%Ru/HZSM-5 catalyst could be recovered completely. This catalyst also showed long lifetime compared to some of the reported catalysts.
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It is appreciated that this work was supported by the National Natural Science Foundation of China (Grant No. 21476057), the Natural Science Foundation of Hebei Province of China (Grant No. B2015202284, B2016202393), and the Program for the Top Young Innovative Talents of Hebei Province of China.