7/28/2019 Hydro Tal Cites

1/1

Hazel Stephenson, Heather Bradshaw,

MEL Chemicals, Clifton Junction, Swinton, Manchester M27 8LS, England.

IntroductionIn 2006 we began development on a

range of hydrotalcites. To date we havebeen focusing our development on

products primarily for use as carbon

dioxide sorbants to complement our

melsorb product range, however there

are a wide variety of applications that

can use hydrotalcites, examples include:

Additives for polymers Anion exchange Antacids Catalysts Catalyst supports Nuclear waste treatment Sorbants

Water purification

Hydrotalcites are formed in nature by the

weathering of basalts or from precipitation

in saline water sources, they are of the

general 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 double

hydroxide structure (LDH). The cations

create an overall positive charge in the

layers, which is balanced by the presence

of anions in the interlayer. These anions in

the interlayer can be exchanged, the order

of preference typically being:

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

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

M+ and M4+ metals can be used to part

substitute M2+ or M3+, this enables fine

tuning of the product to suit specific

applications by reducing or increasing the

overall positive charge, and thus the capacityfor anions, basisity and catalytic activity.

Another interesting property of hydrotalcites

is their memory effect, after relatively

gentle calcination, the double layered

hydroxide structure can be regenerated

by exposure to anions, hence use asregenerable CO2 sorbants.

The mixed oxides resulting from

calcinations of hydrotalcites can be useful

in catalytic applications, due to their high

surface area and large pores, but also the

distribution of metals on the surface.

ProductsUsing our experience in the preparation

of mixed oxides we have been working

on process improvements to the standard

preparation techniques, aiming to give

improved impurity removal, increased

surface area stability and particle size

control. We have developed a productcalled XZO1679/01 which has a Mg: Al : Zr

ratio of 3:0.78 0.14.

Characterisation

Calcination 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 XZO 1679/01

Figure 4: SEM of XZO 1679/01

SummaryHydrotalcites can be used in a variety of

applications. Modifying the structure by

addition of zirconia and/ or alternative

metals gives us the ability to tailor the

product properties to suit the specific

application.

Tuneable properties include:

Activity of supported metal

Basisity

Capacity Kinetics: sorption/ion exchange Particle size Selectivity Surface areaSamplesLaboratory samples of XZO 1679/01 up to

500g and pilot plant samples up to 5kg are

available on request. For larger quantities,

or information on other compositions that

are available please contact:

melchemsales@melchemicals.com or our

agents O.C. Lugo, at info@oclugo.com.

AcknowledgmentsMEL Chemicals / MEI would like to thank

Dr Alexei Lapkin (a.lapkin@bath.ac.uk) and

Alina Iwan at Bath University for their help

measuring CO2 sorption, SEM and

continued support in CO2 sorption projects.

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

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

2. Velu, S. Ramaswamy, V. Ramani,A. Newhydrotalcite-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 mixed

oxides, Chem. Mater. 2002, 14, 1530-1538.4. Braterman, P.S. Xu, Z.P, Yarberry, F. Layered

Double 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+Anions

Water molecules

2.5

2.0

1.5

1.0

0.5

0.00 150 200 25050 100 300

Time (mins)

Wt%

CO2

5000

Aged 0700/2

Aged 0500/2

Aged 0450/2

Aged 0400/2

As Received

4000

3000

2000

1000

010 20 30 50 60

2 Theta

40 70

Counts

Figure 3: XRD of XZO 1679/01

Figure 2: Uptake of CO2 at 25C 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