Abstract:Novel silica nanoboxes were prepared by controlled dealumination of Na-X and Ca-A type zeolites using ammonium hexafluorosilicate (AHFS). The silica-richer the parent zeolite, the smaller the average pore size produced and the narrower the pore size distribution obtained. This was due to the specific reactivity of the extracting agent with the zeolite framework aluminum atoms. High temperature calcination of the dealuminated X-zeolite (ammonium form) resulted in mesoporous materials exhibiting an ink-bottle sh… Show more
“…[1]. In particular, the (m)Al-nanoboxes and the (b)Al-nanoboxes which were the monomodal and the bimodal materials, were obtained by secondary synthesis from the NaX using preferably the following procedures.…”
Section: Secondary Synthesis Of Al-nanoboxesmentioning
confidence: 99%
“…The ammonium forms, namely (m)NH 4 -deal X and (b)NH 4 -deal X respectively, were obtained by ionexchange with ammonium ions [1]. Subsequent calcination at 600°C resulted in (m)H-deal X and (b)H-deal X samples, respectively.…”
Section: Preparation Of the Nh 4 And The Acidic Forms Of The Al-nanobmentioning
confidence: 99%
“…Some of the techniques used to characterize the materials comprising the atomic absorption spectroscopy (AAS) for the determination of the Si/Al ratio, X-ray powder diffraction (in particular at small angle), BET for the determination of textural properties, thermogravimetric (TGA) and differential thermal (DTA) analyses performed in Ar flow, were already described in detail in the previous work [1]. In particular with the technique of X-ray diffraction at small angles, great cares were taken in order to eliminate eventual optical artefacts.…”
Section: Characterization Of the Solid Materialsmentioning
confidence: 99%
“…Novel mesoporous materials, silica nanoboxes [1], were synthesized by controlled dealumination of alumina-rich zeolites (X and A types). In contrast with the synthetic MCM-41 materials [2] which show relatively low thermal and chemical stability [3], the new silica nanoboxes could withstand a temperature of at least 700°C or the loading of triflic acid -a superacidic compound -up to 20-25 wt without undergoing significant structural collapse [1].…”
Section: Introductionmentioning
confidence: 99%
“…Silica nanoboxes were obtained by pore enlargement of zeolite materials using ammonium hexafluorosilicate (AHFS) in buffered solution which ''selectively'' removed some zeolite walls in the way that the newly created nanometer-sized cavities exhibited a quite narrow pore size distribution (monomodal Al-nanoboxes) [1]. However, if some zeolite ''clusters'' were left in these cavities (bimodal Al-nanoboxes), the material underwent a rapid pore closure upon activation at high temperature, resulting in a dramatic decrease in surface area and pore volume.…”
Silica nanoboxes synthesized from alumina-rich zeolites, showed two distinct categories of nano-structured materials. Entirely mesoporous nanoboxes (monomodal Al-nanoboxes) were highly thermally and chemically resistant even in the acidic form whereas calcination at high temperature of materials still containing some zeolite remnants (bimodal Al-nanoboxes), resulted in dramatic loss of surface area and pore volume. Pore closure by mobile and amorphous aluminic species was believed to occur. The high thermal and chemical stability of the monomodal Al-nanoboxes was found to be related to the highly siliceous character of the mesopore walls which contained isolated tetrahedral Al atoms linked to tetrahedral Si atoms. Treatment of the acid form of the bimodal nanoboxes with La or Ce containing solutions resulted in quite thermally stable materials owing to the reduction of the number of protonic sites by the rare-earth metal ions.KEY WORDS: silica nanoboxes from Al-rich zeolites; thermal stability; monomodal; bimodal pore size distribution; structure of the cavity walls.
“…[1]. In particular, the (m)Al-nanoboxes and the (b)Al-nanoboxes which were the monomodal and the bimodal materials, were obtained by secondary synthesis from the NaX using preferably the following procedures.…”
Section: Secondary Synthesis Of Al-nanoboxesmentioning
confidence: 99%
“…The ammonium forms, namely (m)NH 4 -deal X and (b)NH 4 -deal X respectively, were obtained by ionexchange with ammonium ions [1]. Subsequent calcination at 600°C resulted in (m)H-deal X and (b)H-deal X samples, respectively.…”
Section: Preparation Of the Nh 4 And The Acidic Forms Of The Al-nanobmentioning
confidence: 99%
“…Some of the techniques used to characterize the materials comprising the atomic absorption spectroscopy (AAS) for the determination of the Si/Al ratio, X-ray powder diffraction (in particular at small angle), BET for the determination of textural properties, thermogravimetric (TGA) and differential thermal (DTA) analyses performed in Ar flow, were already described in detail in the previous work [1]. In particular with the technique of X-ray diffraction at small angles, great cares were taken in order to eliminate eventual optical artefacts.…”
Section: Characterization Of the Solid Materialsmentioning
confidence: 99%
“…Novel mesoporous materials, silica nanoboxes [1], were synthesized by controlled dealumination of alumina-rich zeolites (X and A types). In contrast with the synthetic MCM-41 materials [2] which show relatively low thermal and chemical stability [3], the new silica nanoboxes could withstand a temperature of at least 700°C or the loading of triflic acid -a superacidic compound -up to 20-25 wt without undergoing significant structural collapse [1].…”
Section: Introductionmentioning
confidence: 99%
“…Silica nanoboxes were obtained by pore enlargement of zeolite materials using ammonium hexafluorosilicate (AHFS) in buffered solution which ''selectively'' removed some zeolite walls in the way that the newly created nanometer-sized cavities exhibited a quite narrow pore size distribution (monomodal Al-nanoboxes) [1]. However, if some zeolite ''clusters'' were left in these cavities (bimodal Al-nanoboxes), the material underwent a rapid pore closure upon activation at high temperature, resulting in a dramatic decrease in surface area and pore volume.…”
Silica nanoboxes synthesized from alumina-rich zeolites, showed two distinct categories of nano-structured materials. Entirely mesoporous nanoboxes (monomodal Al-nanoboxes) were highly thermally and chemically resistant even in the acidic form whereas calcination at high temperature of materials still containing some zeolite remnants (bimodal Al-nanoboxes), resulted in dramatic loss of surface area and pore volume. Pore closure by mobile and amorphous aluminic species was believed to occur. The high thermal and chemical stability of the monomodal Al-nanoboxes was found to be related to the highly siliceous character of the mesopore walls which contained isolated tetrahedral Al atoms linked to tetrahedral Si atoms. Treatment of the acid form of the bimodal nanoboxes with La or Ce containing solutions resulted in quite thermally stable materials owing to the reduction of the number of protonic sites by the rare-earth metal ions.KEY WORDS: silica nanoboxes from Al-rich zeolites; thermal stability; monomodal; bimodal pore size distribution; structure of the cavity walls.
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