Download pdf - Hydrotalcites - MEL Chemicals · Introduction In 2006 we began development on a range of hydrotalcites. To date we have been focusing our development on ... •Antacids •Catalysts

Hazel Stephenson, Heather Bradshaw,MEL Chemicals, Clifton Junction, Swinton, Manchester M27 8LS, England.

IntroductionIn 2006 we began development on arange of hydrotalcites. To date we havebeen focusing our development onproducts primarily for use as carbondioxide sorbants to complement ourmelsorb product range, however thereare a wide variety of applications thatcan use hydrotalcites, examples include:

• Additives for polymers

• Anion exchange

• Antacids

• Catalysts

• Catalyst supports

• Nuclear waste treatment

• Sorbants

• Water purificationHydrotalcites are formed in nature by theweathering of basalts or from precipitationin saline water sources, they are of thegeneral formula:

[M2+1-x M3+x(OH)2x]x+ (An- )x/n.mH2O

M2+ is typically Mg but can be Ni, Zn, Cu.M3+ is typically Al but can be Cr, Mn, Co, Fe.A is any anion.

Hydrotalcites are useful in such a varietyof applications due to their layered doublehydroxide structure (LDH). The cationscreate an overall positive charge in thelayers, which is balanced by the presenceof anions in the interlayer. These anions inthe interlayer can be exchanged, the orderof preference typically being:

NO3- < Br- < Cl- < F- < OH- < SO42-

< CrO42- < HAsO42- < HPO42- < CO32-

M+ and M4+ metals can be used to partsubstitute M2+ or M3+, this enables finetuning of the product to suit specificapplications by reducing or increasing theoverall positive charge, and thus the capacityfor anions, basisity and catalytic activity.Another interesting property of hydrotalcitesis their memory effect, after relatively

gentle calcination, the double layeredhydroxide structure can be regeneratedby exposure to anions, hence use asregenerable CO2 sorbants.The mixed oxides resulting fromcalcinations of hydrotalcites can be usefulin catalytic applications, due to their high surface area and large pores, but also thedistribution of metals on the surface.

ProductsUsing our experience in the preparationof mixed oxides we have been workingon process improvements to the standardpreparation techniques, aiming to giveimproved impurity removal, increasedsurface area stability and particle sizecontrol. We have developed a productcalled XZO 1679/01 which has a Mg : Al : Zrratio of 3:0.78 0.14.

CharacterisationCalcination Surface Area Total porecondition (m2/g) volume(°C / hrs) (ml / g)

Dried 67 0.27

400/2 225 0.60

450/2 193 0.66

500/2 177 0.58

700/2 157 0.73

Figure 1: Table of data for XZO1679/01

Figure 4: SEM of XZO 1679/01

SummaryHydrotalcites can be used in a variety of applications. Modifying the structure byaddition of zirconia and / or alternativemetals gives us the ability to tailor theproduct properties to suit the specificapplication.Tuneable properties include:

• Activity of supported metal

• Basisity

• Capacity

• Kinetics: sorption/ion exchange

• Particle size

• Selectivity

• Surface area

SamplesLaboratory samples of XZO 1679/01 up to500g and pilot plant samples up to 5kg areavailable on request. For larger quantities,or information on other compositions thatare available please contact:[email protected] or ouragents O.C. Lugo, at [email protected].

AcknowledgmentsMEL Chemicals / MEI would like to thankDr Alexei Lapkin ([email protected]) andAlina Iwan at Bath University for their helpmeasuring CO2 sorption, SEM andcontinued support in CO2 sorption projects.

References1. Tsuji, M. et al. Hydrotalcites with an extended

Al3+ substitution: Synthesis, simultaneousTG-DTA-MS study, and their CO2 adsorption behaviors. J. Mater. Res.,1993 8(5).

2. Velu, S. Ramaswamy, V. Ramani, A. New hydrotalcite-like anionic clays containing Zr4+

in the layers. Chem. Commun,. 1997, 2107.3. Tichit, D et al, Preparation of Zr containing

Layered Double Hydroxides and characterizationof the acido-basic properties of their mixedoxides, Chem. Mater. 2002, 14, 1530-1538.

4. Braterman, P.S. Xu, Z.P, Yarberry, F. LayeredDouble Hydroxides. (LDHs) Handbook ofLayered Materials.

5. Das, N.N. et Al, Adsorption of Cr(VI) andSe(IV) from their aqueous solutions onto Zr4+

substituted ZnAl/Mg/Al-layered doublehydroxides: effect of Zr4+ substitution.Colloid and interface science 2004 1-8.

6. Velu. S. et al. Selective production of hydrogenfrom fuel cells via oxidative steam reformingof methanol over CuZrAl(Zr) oxidecatalysts. Applied Cat. 2001, 213 47.

OH-

M2+ or M3+AnionsWater molecules

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Figure 3: XRD of XZO1679/01

Figure 2: Uptake of CO2 at 25ºC for XZO 1679/01

HydrotalcitesP.O. Box 6, Clifton Junction, Swinton,Manchester M27 8LS, England.

Magnesium Elektron Inc., 500 Point Breeze Rd,Flemington, NJ 08822, USA

Nikkei-MEL, 4025-1, Shimizu-Miho, Shizuoka City,Shizuoka Prefecture, 424-0901, Japan.

A Luxfer Group Company