Properties and Characterization of Al₂O₃ and SiO₂-TiO₂ Pillared Saponite

Abstract

Abstract--A saponite pillared with a single (AlzO3) or a mixed (SiO~-TiO:) oxide exhibited basal spacings of 16-19 and 30-40/~, respectively. The pillared structures were found to be stable up to 700~ Water, nitrogen, and high resolution argon adsorption were used to study the effect of thermal treatments on surface chemistry, pore structure, and surface area of these pillared clays. The pillared saponites exhibited a hydrophobic behavior at temperatures > 500~ whereas such behavior was observed at >300~ for montmorillonite. Most of the micropores in the A1203 pillared clays were < 10 A, whereas the SiO2-TiO2 pillared clays showed a broad distribution of pores in both micropore and mesopore regions. The SiO2-TiO2 pillared samples possessed higher surface area compared with A1203 pillared clays. The percent decrease in surface area was smaller for pillared saponites compared with pillared montmorillonites when calcined from 300 ~ to 700~ indicating a higher thermal stability of the former. The pillared clays were also characterized by solid state 27A1 and 295i magic-angle spinning nuclear magnetic resonance (MAS/ NMR) spectroscopy. There was no direct evidence of cross-linking (covalent bonding between the clay layer and pillar) in montmorillonite irrespective of the types of pillars. In saponite, however, a significant structural modification took place. 27A1 spectra of A1203 pillared saponite heated at >300~ appear to indicate an increase in A1 vl as a result, at least in part, of initiation of hydrolytic splitting of Si-O-AI bonds. The actual release of A1 from the tetrahedral sheet probably occurred at a temperature > 500~ and completed around 7000C with the formation of Si-O-Si linkages. The decreased intensity of peak due to Si(1A1) in 29Si spectra of the sample heated at 700~ corroborates the 27A1 MAS/NMR results. Additionally, the 295i spectra indicated a cross-linking between SiO4 (clay sheet) with A1203 pillars, which could be achieved by inverting some silica tetrahedra into the interlayer. 27A1 and 295i spectra of SiOzTiO2 pillared saponite also showed the trend similar to that exhibited by A1203 pillared saponite, indicating that the crystal chemistry of the host may be more important than the nature of pillars in the structural modification and cross-linking behavior of thermally treated pillared clays.

Characterization and catalytic properties of a saponite clay modified by acid activation

“…without prior acid activation) have been prepared previously and are reported to have high thermal stability and good catalytic properties (Urabe et al, 1986;Malla & Komarneni, 1993;Chevalier et al, 1994). Few studies, however, are reported concerning the acid activation of saponite clays (Vicente Rodriguez et al, 1994;Vicente et al, 1996).…”

MINCALC1 — A Spreadsheet for the Rapid Calculation of 2:1 Phyllosilicate Mineral Formulae from Chemical Analyses

“…These same rules were followed for the MINCALC 1 spreadsheet and are as follows: (1) the framework anionic charge is -22, (2) all Si is assigned to the tetrahedral layer to bring the total tetrahedral occupancy to 4 cations, (3) ira charge deficiency occurs in the tetrahedral layer following assignment of silicon, then A1 and possibly Fe 3+ are assigned to the tetrahedral layer to bring the total tetrahedral cation occupancy to 4, (4) any remaining AI as well as Fe (either ferric or ferrous) are then assigned to the octahedral layer for a total octahedral charge of + 6 (for handling both dioctahedral and trioctahedral structures), (5) any remaining charge deficit in the octahedral layer is balanced by the assignment of appropriate amounts of Mg to this layer, and (6) any remaining Mg as well as the other index cations (i.e., Ca, Na, K) are assigned to the interlayer Malla and Komarneni (1993).…”

“…As an example, Malla and Komarneni (1993) listed the results of the chemical analyses and the calculated structural formulae from both a Na-montmorillonite and Na-saponite (Tables 1 and 2). After entering their compositional data (which took < 30 seconds), identical formulae, within rounding error, for these two minerals were calculated using MINCALC 1 ( Table 2).…”

Influência da temperatura de formação do íon de Keggin no processo de pilarização de esmectitas

“…A ordem de grandeza destes parâmetros nas amostras PILC Ta a PILC 105 é equivalente aos de materiais que têm grande acesso a moléculas de pequenas dimensões, como N 2 cujo diâmetro cinético é 3,64 Å [13,18]. As isotermas de adsorção-dessorção de N 2 destes materiais (Figura 6) assemelham-se com as de amostras de saponita pilarizas com Al 13 a 400 o C (amostras STPM e STPS), classificadas segundo BDDT (Brunauer, Deming, Deming, Teller) como isotermas de transição entre os tipos I e IV com histeresis H4 bem definidas [19].…”

“…As relações observadas entre os três últimos parâmetros e a porosidade de argilas pilarizadas estão de acordo com as observações feitas na literatura [2,14,15,16]. Observa-se na Tabela 1 que os valores de volume total de poros nas amostras PILC Ta a PILC 105 são bem próximos aos das amostras STPM e STPS [19] e bem inferiores aos das amostras Loc30, Loc10 e Loc5 [5]. A área específica na amostra PILC Ta é praticamente equivalente a da Loc5.…”