The Kinetics of Ammonia Synthesis over Ruthenium-Based Catalysts: The Role of Barium and Cesium

Ammonia synthesis on graphitic-nanofilament supported Ru catalysts

“…4 shows the catalytic activity for ammonia synthesis on Ru/GNFs-B catalysts with different promoter/Ru atomic ratios under a pressure of 3.0 MPa at 400 • C in a 3:1 mixture of H 2 and N 2 . In these experiments, Ru/GNFs-B promoterd by Ba (Ba/Ru = 0.2 atomic ratio) is the most active for ammonia synthesis among the three kinds of promoters tested probably due to the different roles of the promoters [10]. Its activity is four and two times higher than that of Ru/GNFs-B Promoter/Ru molar ratio promoted by potassium or cesium with a molar ratio of 0.8.…”

“…Davis and co-workers [27] studied ammonia synthesis over zeolite X supported Ru promoted by barium and suggested that the presence of the Ba promoter can create more high activity sites at the interface between the promoter and metal Ru. Recently, Muhler and co-workers [10] and Kowalczyk and co-workers [28] suggested that Ba plays the role of a structural promoter to control the concentration of active sites. In addition, Kowalczyk and co-workers [29] also studied the decomposition of ammonia on Ru promoted by Ba and Cs in detail and found a different effect of Ba and Cs.…”

“…Therefore, a more stable support is required, and this has led to a search for an alternative to active carbon. Recently, a number of studies have shown that graphitzed activated carbon, MgO and BN supported Ru have high catalytic activities and long-term stability for ammonia synthesis [4][5][6][7][8][9][10][11][12][13].…”

Ammonia synthesis over the Ba-promoted ruthenium catalysts supported on boron nitride

“…Studies of the barium-doped Ru catalysts deposited on graphitised carbon [66] or magnesia [21] demonstrate that the samples reach their steady-state level of the reaction rate after a short time of reduction (24-48 h) at 470 and 520°C, respectively. A prolonged activation at 520°C, or above, may even lead to an activity decline due to the sintering of ruthenium particles [40].…”

“…The commercialisation of the Ru/HSAG catalyst has resulted in intensive studies of ruthenium catalysts deposited on various supports such as magnesia [18][19][20][21][22][23][24][25][26][27][28][29][30], magnesium-aluminum spinel [31][32][33][34], zeolites [35][36][37][38] or carbon [39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55], Recently, Jacobsen [56] and Hansen et al [57] from H. Topsoe have revealed that ruthenium supported on boron nitride and promoted with barium is the most efficient catalytic system for NH 3 synthesis that has ever been found. Our paper is also devoted to the Ba-Ru/BN catalysts or, more precisely, to their catalytic properties in NH 3 synthesis.…”