A two-step method of loading controlled amounts of transition metal cations into alumina pillared clays (Al-PILCs) is proposed. First, calcined Al-PILC was dispersed into an aqueous solution of sodium or ammonium ions. Increasing the pH of the dispersion resulted in an increase in the amount of cations loaded into the clay. The ion-doped Al-PILC was then exchanged with an aqueous solution of transition metal salt at a pH of ∼4.5 to replace Na+ or NH4 + ions by transition metal cations. Analytical techniques such as atomic absorption spectroscopy, X-ray diffraction, diffuse reflectance−ultraviolet−visible spectroscopy, as well as N2 adsorption were used to characterize the PILC products with and without the loading of metal ions. The introduced transition metal species exist in the forms of hydrated ions in the PILC hosts. The content of transition metal ions in the final product increased with the amount of Na+ or NH4 + loaded in the first step so that by controlling the pH of the dispersion in the first step, one can control the doping amounts of transition metal cations into Al-PILCs. A sample containing 0.125 mmol/g of nickel was thus obtained, which is ∼3 times of that obtained by directly exchanging Al-PILC with Ni(NO3)2 solution, while the pillared layered structures of the Al-PILC remained. The porosity analysis using N2 adsorption data indicated that most of the doped transition metal ions dispersed homogeneously in the micropores of the Al-PILC, significantly affecting the micropore structure.

Erionite-like silicoaluminophosphate molecular sieve SAPO-17 and levyne-like SAPO-35, in which Ni ions were incorporated via solid-state ion-exchange into known extraframework sites, have been studied by electron spin resonance (ESR) and electron spin echo modulation (ESEM). The Ni ion reducibility, location, and interaction with several adsorbates have been investigated. Among these adsorbates, the interaction with nitric oxide was emphasized and compared to that of Ni ion with NO in the previously studied chabazite-like SAPO-34. Room-temperature adsorption of C 2 D 4 on NiH-SAPO-17 after dehydration at 573 K, oxygen treatment at 823 K, evacuation, and subsequent hydrogen treatment at 573 K produces two Ni-ethylene complexes. Carbon monoxide adsorption gives rise to a Ni(I)-(CO) n complex with unresolved 13 C hyperfine lines. Following the kinetics of nitric oxide adsorption on NiH-SAPO-17 shows that initially, a Ni(I)-(NO) + complex, a NO radical, and a new species which appears to be another NO species are generated. After a reaction time of 24 h, NO 2 is observed. As the adsorption time further increases, NO 2 becomes stronger while Ni(I)-(NO) + decays, and after 5 days only NO 2 remains. NO adsorption on NiH-SAPO-35 shows different features. Initially, two Ni(I)-(NO) + complexes along with a NO radical are seen. As the adsorption time increases, one of the Ni(I)-(NO) + complexes decreases in intensity while the other one increases, and after a few days only one Ni(I)-(NO) + complex remains. Simulation of the 31 P ESEM spectrum, supplemented by 27 Al modulation, suggests that, upon dehydration, Ni ions in NiH-SAPO-17 migrate from the erionite supercage to the smaller cancrinite cage. In dehydrated NiH-SAPO-34 and NiH-SAPO-35, Ni ions remain in the large chabazite and levyne cages, respectively. As a consequence, Ni(II) in NiH-SAPO-17 is less sensitive to reduction by hydrogen than it is in NiH-SAPO-34 and NiH-SAPO-35.

The synthetic incorporation of transition metal ions into aluminophosphate and silicoaluminophosphate molecular sieve frameworks is studied by electron spin−echo modulation (ESEM) spectroscopy. Based mainly on bulk chemical composition of the product, it has been suggested that divalent and trivalent metal ions such as Mn(II), Co(II), Cr(III), and Fe(III) substitute for framework aluminum sites. On the basis of 31P ESEM results, we originally suggested a framework phosphorus site for the incorporation of metal ions such as Ni(II) and Cr(III) in NiAPSO-5 and CrAPSO-5 molecular sieves. This site was later supported for other metal ions such as Ti(IV), V(IV), and Cu(II). In this work, we have extended such studies to Mn(II) and Fe(III) to better understand the metal substitution sites in AlPO4 frameworks. Irrespective of the particular metal ion, the 31P ESEM spectra of MeAPO/MeAPSO molecular sieves can be interpreted best on the basis of metal incorporation at a framework phosphorus site. Strong 27Al modulations are also observed for these materials, which supports the 31P ESEM result that incorporated metal ions are located nearer to aluminum than phosphorus.

The formation of monovalent palladium in PdNaK-clinoptilolite where Pd(II) is introduced into extraframework sites as [Pd(NH 3 ) 4 ] 2+ by liquid-state ion exchange at 298 K, is compared to that observed in PdH-clinoptilolite where Pd(II) is incorporated by solid-state ion exchange at 823 K, using electron spin resonance (ESR) and electron spin-echo modulation (ESEM) spectroscopies. Dehydration at 473 K produces one Pd(I) species in PdH-clinoptilolite but no ESR signal in PdNaK-clinoptilolite. This indicates that the stability of Pd(I) between PdH-clinoptilolite and PdNaK-clinoptilolite is different, probably due to the different locations and environments of Pd in these systems. Hydrogen reduction of Pd(II) in these two materials after activation reveals that Pd(II) ions in PdNaK-clinoptilolite occupy relatively accessible sites in comparison to those in PdH-clinoptilolite. The interactions of Pd(I) formed by thermal reduction of PdH-clinoptilolite with various adsorbates are also studied. The ESR studies coupled with ESEM measurements show that Pd(I) in PdH-clinoptilolite interacts rapidly with molecules smaller than methanol, such as hydrogen, water, ammonia, and carbon monoxide, and forms a stable complex with them. However, adsorption of benzene and pyridine on thermally reduced PdH-clinoptilolite produces no ESR signal due to a Pd(I)-benzene complex or a Pd(I)-pyridine complex, suggesting that Pd(I) is located at a site in eight-ring channels where benzene and pyridine are too big to enter.