Catalytic role of intercalated Pt complex in thermal decomposition of nitrate-type hydrotalcite to porous structure

Thermal decomposition of PtCl6-exchanged hydrotalcite-like Mg0.74Al0.26(OH)(2)(NO3)(0.26)center dot 0.36H(2)O (Pt-HT) in a stream of H-2 has been investigated to demonstrate the catalytic role of intercalated Pt on the transformation to porous structures. Platinum species in the interlayer promoted the reaction between H-2 and interlayer nitrate (NO3- ) to yield N-2 so as to give rise to a large surface area (>= 200 m(2) g(-1)) solid at as low as ca. 200 degrees C, compared to 400 degrees C required for the pristine HT. The XAFS analysis of the PtCl6-exchanged HT gave evidence that part of chloride (Cl-) ligands bound to Pt was replaced by NO3- during an exchange process. Since molecular hydrogen is activated by Pt, the reaction of nitrate ligand with hydrogen to form N-2/H2O should generate a vacant site, which is successively occupied by NO3- ions lying in the interlayer. Such coordination/catalytic reduction cycles would accelerate the removal of NO3- surrounding Pt in the interlayer before dehydroxylation of brucite layers. This is in contrast to the pristine HT, where the release of NO3- as NO and dehydroxylation occurred simultaneously at >= 400 degrees C. Consequently, N-2 adsorption/desorption isotherms showed the two-dimensional pore structure of Pt-HT in contrast to the three-dimensional pores of the pristine HT after thermal decomposition.