Energy Efficient and Intermittently Variable Ammonia Synthesis over Mesoporous Carbon-Supported Cs-Ru Nanocatalysts

Abstract

The Cs-promoted Ru nanocatalysts supported on mesoporous carbon materials (denoted as Cs-Ru/MPC) and microporous activated carbon materials (denoted as Cs-Ru/AC) were prepared for the sustainable synthesis of ammonia under mild reaction conditions (<500 °C, 1 MPa). Both Ru and Cs species were homogeneously impregnated into the mesostructures of three commercial available mesoporous carbon materials annealed at 1500, 1800 and 2100 °C (termed MPC-15, MPC-18 and MPC-21, respectively), resulting in a series of Cs-Ru/MPC catalysts with Ru loadings of 2.5–10 wt % and a fixed Cs loading of 33 wt %, corresponding to Cs/Ru molar ratios of 2.5–10. However, the Ru and Cs species are larger than the pore mouths of microporous activated carbon (shortly termed AC) and, as a consequence, were mostly aggregated on the outer surface of the Cs-Ru/AC catalysts. The Cs-Ru/MPC catalysts are superior to the Cs-Ru/AC catalyst in catalysing mild ammonia synthesis, especially for the 2.5Cs-10Ru/MPC-18 catalyst with a Ru loading of 10 wt % and a Cs/Ru ratio of 2.5, which exhibited the highest activity across a wide SV range. It also showed an excellent response and stability during cycling tests over a severe temperature jump in a short time, presumably due to the open mesoporous carbon framework and suitable surface concentrations of CsOH and metallic Ru species at the catalytically active sites. This 2.5Cs-10Ru/MPC-18 catalyst with high activity, fast responsibility and good stability has potential application in intermittently variable ammonia synthesis using CO2-free hydrogen derived from electrolysis of water using renewable energy with fast variability.

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).…”

Recent Advances in Heterogeneous Catalysis for Ammonia Synthesis

“…The CsÀ Ru/MC exhibited excellent response and stability during recycling tests over severe temperature jumps in a short time due to the mesoporous carbon framework and promoter. [142,154] Li et.al., synthesized, Ru nano particle of size 1.5-2.5 nm, semi embedded in mesoporous carbon (BaÀ K/RuÀ MC) by novel RuCl 3 / SiO 2 template approach with Ba/K promoter exhibiting higher catalytic activity than just supported catalyst Ba/K/Ru/MC. Further, incorporation of N in carbon matrix greatly improves catalytic activity of Ba/RuÀ N-MC due to SMSI and change in the electronic properties of metallic Ru.…”

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

“…A microporous activated carbon (product code: HG15-119, denoted as AC) was obtained from Osaka Gas Chemical Co., Ltd., Osaka, Japan) and used after pretreatment at 500 • C for 3 h in H 2 (100 mL min −1 ). In a typical synthesis procedure, 1 g of MPC or AC support was dispersed in 70 mL of an ethanol-based impregnation solution (50%, v/v), containing 0.31 g of nitrosylruthenium(III) nitrate (Ru(NO)(NO 3 ) 3 ) (31.4 wt% Ru; Mitsuwa Chemicals Co., Ltd., Osaka, Japan), and slowly evaporated at 70-80 • C. The dried solids were thermally treated at 400 • C for 3 h in N 2 ((ramp rate = 5 • C min −1 ), resulting in MPCand AC-impregnated Ru catalysts with Ru loading of 10 wt% (10Ru/MPC and 10Ru/AC, respectively) [21,32]. Barium nitrate (Ba(NO 3 ) 2 , 0.41 g, 52.5 wt% Ba; Wako Pure Chemical Industries Ltd., Osaka, Japan) was then impregnated into the 10Ru/MPC and 10Ru/AC samples using the aforementioned procedure except for the calcination step.…”

“…The maximum ammonia synthesis rate was observed from the curves inFigure 4and corresponding reaction temperature 2. The Cs/Ru molar ratio was referred to our recent study[32].…”