Synthesis of Smectites and Porous Pillared Clay Catalysts: A Review (original) (raw)
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Effect of Pt on Catalytic Activity of Al- and Zr-Pillared Smectite
Asian Journal of Chemistry, 2016
Clays are known as one of the inorganic materials with some applications especially as catalyst and adsorbent in industries. The potency of porosity and also modifiable structure of clays have been reported as high potential for developing smart inorganic materials. For those purposes, clays particularly smectite class are modified related to their application [1-3]. Smectite clays are modified with metals or oxides in order to enhance the activity regarding to the specific catalytic reactions instead of to cover the limitation related to its lack of the structure stability in high temperature. Metal oxide pillared clays are popular method in clay modification scheme. The pillarization process consists of the metal oxide insertion between the interlayer region of clays and have been reported to give sufficiently thermal stability. Among some metal oxide such as Ti, Cr, Zr and Zn, Al and Zr were intensively reported for catalysis purposes [4-8]. Preparation of Aland Zr-pillared smectite involving pillared montmorillonite and pillared saponite were reported to be active as catalyst in many reactions such as hydrogenation, esterification, etc. Not only as catalysts itself, both materials are potential to be utilized as catalyst support from their thermal stability and easily prepared. In previous works Al-pillared montmorillonite (Al-PILM) was reported to have high catalytic activity in hydro
Journal of Porous Materials, 2001
Metal oxide pillared clay (PILC) possesses several interesting properties, such as large surface area, high pore volume and tunable pore size (from micropore to mesopore), high thermal stability, strong surface acidity and catalytic active substrates/metal oxide pillars. These unique characteristics make PILC an attractive material in catalytic reactions. It can be made either as catalyst support or directly used as catalyst. This paper is a continuous work from Kloprogge's review (J.T. Kloprogge, J. Porous Mater. 5, 5 1998) on the synthesis and properties of smectites and related PILCs and will focus on the diverse applications of clay pillared with different types of metal oxides in the heterogeneous catalysis area and adsorption area. The relation between the performance of the PILC and its physico-chemical features will be addressed.
Clays & Clay Minerals, 1996
Ce/Al-and La/Al-pillared smectites were prepared by cation exchange of bentonite, saponite and laponite with hydrothermally treated (130-160 ~ for 16-136 h) solutions containing mixtures of aluminumchlorohydrate (ACH) and Ce3+-/and La3+-salts. After calcination at 500 ~ the pillared products are characterized by basal spacings between 24.8 and 25.7 ,~ and surface areas of approximately 430 m 2 g 1. The products are hydrothermally stable at 500 ~ after 2 h in steam. The large basal spacings are due to the formation of a large Ce/La-bearing Al-polyoxocation, whose formation is favored by initially high Al concentrations ~3.7 M and an OH/Al molar ratio of approximately 2.5. The Ce/Al or La/Al molar ratios can be as low as 1/30. 27Al nuclear magnetic resonance (NMR) spectroscopy has shown that the polyoxocation has a higher Altetrahedral/Aloctahedral ratio than the Keggin structure Al13, which may partly explain the higher stability compared to normal Al-pillared clays. Hydroconversion of n-heptane indicated that the activity of the Pt-loaded pillared products is higher than that of a conventional Pt-loaded amorphous silica-alumina catalyst. Selectivity is strongly dependent on the type of starting clay and its acidity. In industrial hydrocracking of normal feedstock, a Ni/W-loaded Ce/Al-pillared bentonite catalyst showed rapid deactivation due to coke-formation reducing the surface area and the pore volume. Additionally, coke-formation is facilitated by the relatively high iron content of the pillared bentonite (3.43 wt% Fe203).
Pillared clays with Al–Fe and Al–Ce–Fe in concentrated medium: Synthesis and catalytic activity
Applied Catalysis A-general, 2009
This paper proposes a new methodology for the modification of clays with the mixed Al-Fe and Al-Ce-Fe systems, which involves the synthesis of solid polymeric precursors and their use as pillaring agents in the modification of clays. The process of intercalation of clay with Al 13 , Al 13 + Fe and Al 13 + Ce + Fe nitrate was performed using ultrasound. The pillaring agents Al 13 , Al 13 + Fe and Al 13 + Ce + Fe were characterized by XRF, XRD, SEM and 27 Al NMR techniques, and pillared clays were characterized by XRF, XRD and N 2 adsorption to 77 K. The catalytic properties of pillared clays were evaluated using catalytic wet peroxide oxidation of phenol in dilute aqueous medium, demonstrating activity comparable to that of solids modified by the conventional method. ß
Solid acid catalysts from clays
Applied Catalysis A: General, 2000
Alumina-pillared and double-pillared montmorillonite and saponite samples have been prepared and characterised from the point of view of their thermal stability, porosity and structure. Surface acidity was studied by ammonia TPD, iso-propanol conversion and n-butene skeletal isomerisation catalysis, and by FT-IR spectroscopy of the surface hydroxy-groups, and of adsorbed acetonitrile and pivalonitrile.
Synthesis and Characterization of Heterogeneous Catalysts and Comparison to Iron-ore
Journal of Chemical Engineering & Process Technology, 2016
The placement of metal oxide pillars between clay mineral layers modifies their physicochemical properties, including surface area, acidity, and catalytic activity. Aluminum is the most commonly used pillar cation, but the use of Fe offers a distinct opportunity to expand the range of catalytic behavior. The purpose of this study was to prepare Al-Fe-pillared smectite and to characterize the resulting materials. Al-Fe-pillared clay was synthesized from Tunisian clay precursors according to a common procedure: grinding, sieving, Na exchange, pillaring, drying and calcinations. Smectite suspension was mixed with different pillaring solutions containing Al and Fe oligomers with Fe/ (Al+Fe) percent ratios: 1; 5; 10 and 50%. Other types of material were investigated in this work; natural iron-ore was defined and characterized as heterogeneous catalysis. The structural and textural properties of synthesis and natural catalysis have been determined by X-ray diffraction, nitrogen adsorption-desorption isotherms, Transmission Electron Microscopy (MET), X-ray fluorescence, CEC and infrared spectroscopy.
Applied Catalysis A: General, 1993
The pore structure and the acidic properties of pillared clays based on montmorillonite and hectorite intercalated with aluminium-, zirconium-and chromium-hydroxy oligomers are compared. Furthermore, the catalytic activity of these catalysts was analyzed in the case of toluene disproportionation. Except for the zirconium-pillared clay the other catalysts show BET surfaces between 250 ma/g and 300 mx/g up to a temperature of 400°C. At higher temperatures the structure collapses because of dehydroxylation of the clay sheets All pillared clay catalysts show a bimodal pore-size distribution with macro-pores between the primary clay crystals. The acidity is characterized by means of IR-spectroscopy with pyridine as sensor molecule. Chromium-pillared clays have stronger Lewis-acid sites than the other pillared clays. The number of Lewis-sites correlates with the number of pillars, whereas the Brenstedacid sites are mainly located in the clay sheets The metal concentration in the dispersion of oligomersolution and clay-mineral is a preparation parameter, which influences the pillar density. An Al-montmorillonite has higher Lewis-and Brensted-acidity than a comparable Al-he&&m. Among the tested catalysts pillared clays based on chromium are most active for the choosen model reaction because of their large macroporosity and the existence of strong Lewis-acid sites. In comparison to a H-ZSM-5 and a H-Y-zeolite the catalytic activity of the optimal Cr-pillared clay is between the activities of these catalysts. Furthermore coking mainly takes place on Brensted-acid sites especially during the first minutes of reaction. The effective stationary kinetics of toluene disproportionation catalyzed by the optimal Cr-pillared clay can be described by a pseudo-first order expression for the reaction velocity.
Preparation of Al/Fe-Pillared Clays: Effect of the Starting Mineral
Materials (Basel, Switzerland), 2017
Four natural clays were modified with mixed polyoxocations of Al/Fe for evaluating the effect of the physicochemical properties of the starting materials (chemical composition, abundance of expandable clay phases, cationic exchange capacity and textural properties) on final physicochemical and catalytic properties of Al/Fe-PILCs. The aluminosilicate denoted C2 exhibited the highest potential as starting material in the preparation of Al/Fe-PILC catalysts, mainly due to its starting cationic exchange capacity (192 meq/100 g) and the dioctahedral nature of the smectite phase. These characteristics favored the intercalation of the mixed (Al13-x/Fex)7+ Keggin-type polyoxocations, stabilizing a basal spacing of 17.4 Å and high increase of the BET surface (194 m²/g), mainly represented in microporous content. According to H₂-TPR analyses, catalytic performance of the incorporated Fe in the Catalytic Wet Peroxide Oxidation (CWPO) reaction strongly depends on the level of location in mixed ...