Structural transformation of kaolin as an active matrix for the in situ synthesis of zeolite Y

Abstract

To produce an optimized matrix for the in situ crystallization of zeolite Y, a commercial kaolin chemically treated with NaOH solution at 97°C for 24 h and thermally transformed from 750 to 1100°C was studied. The kaolin calcined at 750°C has 20% more reactive tetrahedral aluminium species for the synthesis of zeolite Y than kaolin calcined at 865°C. The kaolin calcined at 1000°C has amorphous silica zones that may be extracted using caustic solution; this increases the surface area by a factor of 16 and generates mesopores ~5 nm in diameter. These structural changes in the calcined and treated kaolins were combined to prepare microspheres of the mesoporous matrix, upon which well-dispersed crystals of zeolite Y crystallized.

Synthesis and catalytic behavior of FCC catalysts obtained from kaolin by the in-situ method

“…As shown in our previous report, the alkaline treatment leads to an increasing of the external surface area and the amount of mesopores between 3 and 10 nm in the matrix (Fig. 1) (Padilla et al 2020). Thus, the matrix M-Na with only 7.4% of silicon moles removed, have shown a BET area of 24 m 2 /g and 5.5 times more pore volume compared with the matrix M (Table 1).…”

“…In previous reports, the use of kaolin as a precursor for the synthesis of zeolites has been demonstrated usually from a single phase of calcined kaolin (Patrylak et al 2001;Zhang and Xiong 2012). However, the current study choices each of the matrix components based on a preliminary analysis of the structural changes of raw kaolin (Padilla et al 2020). Thus, the mass ratio of different kaolin phases (K, K-1000, K-1000A and K-1100) used to obtain the matrices M and M-Na, aimed the fact that K-1100 provides mechanical resistance to the particle, while K-1000 is a soluble silica-rich phase which can be added as a source of silicon to reaction mixture or partially extracted with alkali (K-1000A) prior to zeolite synthesis to increase the external area of the matrix.…”

“…The samples were named K-1000 and K-1100, respectively. After calcination, K-1000 was alkaline treated at 95 °C for 24 h using an aqueous solution 3.5 M of NaOH (5 mL/g of calcined kaolin) and identified as K-1000A (Padilla et al 2020).…”

“…The gradual removal of water molecules induces a coordination change in the octahedral (Al VI ) towards tetrahedral (Al IV ) aluminum environments (Sperinck et al 2011;Yan et al 2017;White et al 2010). This Al IV is used as an active source of aluminum during the in-situ synthesis of the zeolite NaY (Padilla et al 2020). Additionally, the content of amorphous material in matrices is related to the mixture of kaolin phases calcined at different temperatures that are linked with sodium silicate acting as a binder.…”

In situ synthesis of zeolites by geopolymerization with NaOH/KOH mixed solution and their potential application for Cd(II) immobilization in paddy soil

“…Geopolymers are alkali-activated (alumino)silicate cementitious materials that have been used in construction materials, fireresistant materials and heavy-metal adsorption and solidification (Davidovits, 1991;Temuujin et al, 2009;Shaqour et al, 2017;Ng et al, 2018;Esaifan et al, 2019;Rasaki et al, 2019;Padilla et al, 2020). The typical manufacturing process of geopolymers involves the addition of an alkaline activator (a mixed solution of sodium or potassium hydroxide and sodium or potassium silicate) to a poorly crystallized or amorphous aluminosilicate material such as fly ash or metakaolin (MKn) and subsequent mixing and curing at a moderate temperature (20-95°C).…”