Standard Synthesis Conditions Research Articles

Zeolite Synthesis in the Presence of Metallosiloxanes for the Quantitative Encapsulation of Metal Species for the Selective Catalytic Reduction (SCR) of NOx.

Metal encapsulation in zeolitic materials through one-pot hydrothermal synthesis (HTS) is an attractive technique to prepare zeolites with a high metal dispersion. Due to its simplicity and the excellent catalytic performance observed for several catalytic systems, this method has gained a great deal of attention over the last few years. While most studies apply synthetic methods involving different organic ligands to stabilize the metal under synthesis conditions, here we report the use of metallosiloxanes as an alternative metal precursor. Metallosiloxanes can be synthesized from simple and cost-affordable chemicals and, when used in combination with zeolite building blocks under standard synthesis conditions, lead to quantitative metal loading and high dispersion. Thanks to the structural analogy of siloxane with TEOS, the synthesis gel stabilizes by forming siloxane bridges that prevent metal precipitation and clustering. When focusing on Fe-encapsulation, we demonstrate that Fe-MFI zeolites obtained by this method exhibit high catalytic activity in the NH3 -mediated selective catalytic reduction (SCR) of NOx along with a good H2 O/SO2 tolerance. This synthetic approach opens a new synthetic route for the encapsulation of transition metals within zeolite structures.

Zeolite Synthesis in the Presence of Metallosiloxanes for the Quantitative Encapsulation of Metal Species for the Selective Catalytic Reduction (SCR) of NOx

AbstractMetal encapsulation in zeolitic materials through one‐pot hydrothermal synthesis (HTS) is an attractive technique to prepare zeolites with a high metal dispersion. Due to its simplicity and the excellent catalytic performance observed for several catalytic systems, this method has gained a great deal of attention over the last few years. While most studies apply synthetic methods involving different organic ligands to stabilize the metal under synthesis conditions, here we report the use of metallosiloxanes as an alternative metal precursor. Metallosiloxanes can be synthesized from simple and cost‐affordable chemicals and, when used in combination with zeolite building blocks under standard synthesis conditions, lead to quantitative metal loading and high dispersion. Thanks to the structural analogy of siloxane with TEOS, the synthesis gel stabilizes by forming siloxane bridges that prevent metal precipitation and clustering. When focusing on Fe‐encapsulation, we demonstrate that Fe‐MFI zeolites obtained by this method exhibit high catalytic activity in the NH3‐mediated selective catalytic reduction (SCR) of NOx along with a good H2O/SO2 tolerance. This synthetic approach opens a new synthetic route for the encapsulation of transition metals within zeolite structures.

Effect of hydrothermal synthesis environment on the particle morphology, chemistry and magnetic properties of barium hexaferrite

Barium nitrate and iron nitrate have been used as precursors in the hydrothermal synthesis of barium hydroxide, iron oxide and barium hexaferrite sols under specified standard synthesis conditions (temperature, time, stirring, alkali concentration, amount of water and heating rate) as a function of the base species used during synthesis. The hydrothermal synthesis of barium hydroxide and iron oxide has been used to develop an understanding of the hydrothermal synthesis of barium hexaferrite from a mixture of their precursors. The investigation has shown that the nucleation and growth behaviour as well as the phase composition, thermal behaviour, particle size, particle-size distribution and magnetic properties are strong functions of the base species used. The electrostatic potential difference between the barium hydroxide and the iron oxide decreases with increasing cation size in the order NaOH, KOH, (C2H5)4NOH and NH4OH. Note the potential difference between the two sol species determines their tendency to coagulate into clusters; hence, the heterocoagulation will be greater when using NaOH or KOH than (C2H5)4NOH or NH4OH. Under the standard synthesis conditions, only NaOH and KOH are able to facilitate the formation of plate-like particles of barium hexaferrite. In contrast, ultrafine particles of iron oxide (10–20 nm) together with only a small amount of barium hexaferrite are produced when either NH4OH or (C2H5)4NOH base is used. The samples synthesized in the presence of the NaOH and KOH exhibit relatively higher saturation magnetization (i.e. 258 mT (39 e.m.u.g−1) and 215 mT (32 e.m.u.g−1), respectively) than those samples synthesized in the presence of NH4OH or (C2H5)4NOH which exhibit negligible saturation magnetization owing to the small amount of magnetic phase (BaFe12O19) present.