Mild Ammonia Synthesis over Ba-Promoted Ru/MPC Catalysts: Effects of the Ba/Ru Ratio and the Mesoporous Structure

Abstract

A series of novel mesoporous carbon-supported, Ba-promoted, Ru catalysts with Ba/Ru ratios of 0.1–1.6 and a Ru loading of 10 wt% (denoted as 0.1–1.6Ba-10Ru/MPC) were prepared via stepwise impregnation of Ru and Ba precursors on the mesoporous carbon materials. The catalysts were applied to mild ammonia synthesis and compared to reference materials, including an analog of the prepared catalyst with a Ba/Ru ratio of 1.6 and a Ru loading of 10 wt% (denoted as 1.6Ba-10Ru/AC). Characterization by X-ray diffraction (XRD), nitrogen physisorption, and electronic microscopy revealed that the 0.1–1.6Ba-10Ru/MPC catalysts contained Ru particles (approximately 2 nm) that were well-dispersed on the mesoporous structure and nanostructured Ba(NO3)2 species. These species decomposed into amorphous BaOx species, acting as a promoter on the metallic Ru particles forming catalytically active sites for ammonia synthesis. All the 0.1–1.6Ba-10Ru/MPC catalysts showed a synergistic effect of the active Ba and Ru species, which were stabilized in the mesoporous carbon framework with fast molecular diffusion and could effectively catalyze mild ammonia synthesis (280–450 °C and 0.99 MPa) even under intermittently variable conditions, particularly for those with Ba/Ru ratios of >0.5. In contrast, the 1.6Ba-10Ru/AC analog showed poor activity and stability for ammonia synthesis due to the sintering of Ba and Ru particles on the outer surface of the microporous carbon framework, resulting in low molecular diffusion and weak synergistic effect of the catalytically active sites.

Effect of Pd Precursor Salts on the Chemical State, Particle Size, and Performance of Activated Carbon-Supported Pd Catalysts for the Selective Hydrogenation of Palm Biodiesel

“…All samples presented a broad peak centered at approximately 640–660 °C. This was ascribed to the thermal instability of AC, which formed gas products such as CH 4 , CO, and CO 2 via the methanation and thermal decomposition reactions of microporous carbon framework under a reducing atmosphere ( Supplementary Figure S1 ) [ 40 , 41 , 42 , 43 ]. The peaks at high temperature in the H 2 -TPR profiles of the prepared Pd catalysts were stronger than that of AC, and that was attributed to the dissociation of H 2 being facilitated over Pd nanoparticles and spilled to the surface of AC (i.e., the spillover effect).…”

“…The MS signals of H 2 , CH 4 , CO, and CO 2 were monitored by the m/z ratios of 2, 16, 28, and 44, respectively. Note that the CO and CO 2 were formed by thermal decomposition of AC, while CH 4 was formed by methanation of AC ( Supplementary Figure S1 ) [ 40 , 41 , 42 , 43 ]. The powdered X-ray diffraction (XRD) patterns of the catalysts were recorded using an X’Pert PRO (PANalytical, Netherlands) XRD system with Cu Kα radiation ( λ = 1.5406 Å), in the 2 θ range of 10–80° at a scanning rate of 0.04° s −1 .…”

Process Intensification Strategies for Power-to-X Technologies

“…Ruthenium-based catalysts were identified as a promising material for NH 3 synthesis under milder reaction conditions due to their high catalytic activity [32]. Recent studies showed that the synthesis of NH 3 at pressures below 10 bar and at temperatures between 300 and 400 • C was feasible [33,34], which provided a decrease in energy demand (i.e., for synthesis gas compression). Furthermore, a fast response and a high stability towards the thermal cycling was demonstrated [35].…”

On Optimal Barium Promoter Content in a Cobalt Catalyst for Ammonia Synthesis

“…For the catalysts in the reduced form (Figure 3b), signals derived from Ba(NO 3 ) 2 are not detected. According to the literature reports [33], Ba(NO 3 ) 2 is transformed into amorphous BaO x species under ammonia synthesis reaction conditions. The subsequent reaction of BaO x species with atmospheric CO 2 could cause the formation of BaCO 3 particles (exsitu XRPD measurements for the catalyst samples removed from the ammonia synthesis reactor).…”