Co-Assembled Supported Catalysts: Synthesis of Nano-Structured Supported Catalysts with Hierarchic Pores through Combined Flow and Radiation Induced Co-Assembled Nano-Reactors

Abstract

Abstract:A novel generic method of silica supported catalyst system generation from a fluid state is presented. The technique is based on the combined flow and radiation (such as microwave, thermal or UV) induced co-assembly of the support and catalyst precursors forming nano-reactors, followed by catalyst precursor decomposition. The transformation from the precursor to supported catalyst oxide state can be controlled from a few seconds to several minutes. The resulting nano-structured micro-porous silica supported catalyst system has a surface area approaching 300 m 2 /g and X-ray Diffraction (XRD)-based catalyst size controlled in the range of 1-10 nm in which the catalyst structure appears as lamellar sheets sandwiched between the catalyst support. These catalyst characteristics are dependent primarily on the processing history as well as the catalyst (Fe, Co and Ni studied) when the catalyst/support molar ratio is typically 0.1-2. In addition, Ca, Mn and Cu were used as co-catalysts with Fe and Co in the evaluation of the mechanism of catalyst generation. Based on extensive XRD, Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) studies, the micro-and nano-structure of the catalyst system were evaluated. It was found that the catalyst and silica support form extensive 0.6-2 nm thick lamellar sheets of 10-100 nm planar dimensions. In these lamellae, the alternate silica support and catalyst layer appear in the form of a bar-code structure. When these lamellae structures pack, they form the walls of a micro-porous catalyst system which typically has a density of 0.2 g/cm 3 . A tentative mechanism of catalyst nano-structure formation is provided based on the rheology and fluid mechanics of the catalyst/support precursor fluid as well as co-assembly nano-reactor formation during processing. In order to achieve these structures and characteristics, catalyst support must be in the form of silane coated silica nano-particles dispersed in water which also contains the catalyst precursor nitrate salt. This support-catalyst precursor fluid must have a sufficiently low viscosity but high elastic modulus (high extensional viscosity) to form films and bubbles when exposed to processing energy sources such as microwave, thermal, ultra-sound or UV-radiation or their combination. The micro-to-nano structures of the catalyst system are essentially formed at an early stage of energy input. It is shown that the primary particles of silica are transformed to a proto-silica particle state and form lamellar structures with the catalyst precursor. While the nano-structure is forming, water is evaporated leaving a highly porous solid support-catalyst precursor which then undergoes decomposition to form a silica-catalyst oxide system. The final catalyst system is obtained after catalyst oxide reduction. Although the XRD-based catalyst size changes slightly during the subsequent heat treatments, the nano-structure of the catalyst system remains substantially unaltered as evaluated through TEM images. Howev...

Plasma Generating—Chemical Looping Catalyst Synthesis by Microwave Plasma Shock for Nitrogen Fixation from Air and Hydrogen Production from Water for Agriculture and Energy Technologies in Global Warming Prevention

“…There were no discernable differences in P* values, as well as with respect to the catalyst properties such as crystallite size and surface area, between the catalysts synthesized from the fresh and stored (four years) catalyst precursor fluids. As shown previously [1], in the case of Fe/Si, the catalyst precursor fluid gradually gels and NO x starts to evolve due to the decomposition of ferric nitrate, especially when the fluid is exposed to light.…”

“…25 mol%) the surface area is in fact higher than that of the support, SiO 2 , indicating that the size of the catalyst crystallites is smaller than that of the support at 7 nm. It can also be seen that the Mn/Si catalyst obtained by the incipient wet impregnation method using uncoated silica with similar silica size (5 nm) yields a smaller surface area because of the difference in the preparation methods as detailed previously [1].…”

“…Spinel-or perovskite-catalyst regeneration can also be carried out using combustion gases (CO 2 + N 2 ) when CO 2 is converted to CO. The present study is an extension of recent studies by the author [1][2][3] on catalyst, plasma reactor/process design, and NH 3 /fertilizer synthesis. Below, a brief review of the relevant studies is given.…”

“…In these catalysts, the oxide spinels Co 3 O 4 and Mn 3 O 4 are the main components of the catalysts. It was shown previously [1] that when the BET surface areas are normalized with respect to density of the catalyst, at high catalyst concentrations (above ca. 25 mol%) the surface area is in fact higher than that of the support, SiO 2 , indicating that the size of the catalyst crystallites is smaller than that of the support at 7 nm.…”

“…Coupled with an efficient preservation and utilization of water which will prevent the Food, Energy and Water shortages that are deemed to emerge as a result of global warming and population increase. Agriculture consumes 85% of global water and NH 3 supply [1,3]. Ammonia itself consumes 87% of the industrial energy, which accounts for ca.…”