Electron Spin Resonance and Electron Spin−Echo Modulation Studies of Synthesized NiAPSO-34 Molecular Sieve and Comparison with Ion-Exchanged NiH−SAPO-34 Molecular Sieve

Abstract

The formation of monovalent nickel in where nickel is believed to be incorporated into the framework of SAPO-34, and its interaction with several adsorbates are compared to Ni(I) species formed in NiH-SAPO-34, where Ni(II) is incorporated by solid-state ion exchange into known extraframework sites using electron spin resonance (ESR) and electron spin-echo modulation (ESEM) spectroscopies. Dehydration at temperatures above 573 K and hydrogen treatment at 573 K as well as γ-irradiation at 77 K produce one nickel species assigned by ESR as isolated Ni(I) in the two samples. Even though the ESR parameters of isolated Ni(I) species are similar after reduction, NiAPSO-34 and NiH-SAPO-34 show noticeable differences in their ESR characteristics after adsorption of various adsorbates, suggesting that Ni(I) in these two materials is in different sites. As a supplement to this, ESEM studies of 31 P and 27 Al, used to ascertain the location of the incorporated paramagnetic transition metal ion, also show significant differences in the modulation patterns. Simulation of the 31 P modulation observed for NiH-SAPO-34 shows two nearest-neighbor phosphorus atoms at 3.9 Å and three next-nearest-neighbor phosphorus atoms at 6.5 Å, indicating that Ni(I) is at site II′ in the chabazite cage near a six ring window after reduction. The 31 P simulation for NiAPSO-34 shows three nearestneighbor phosphorus atoms at a distance of 4 Å and two next-nearest-neighbor phosphorus atoms at 5.3 Å. This is consistent with Ni(I) ions substituting into a framework phosphorus site. In as-synthesized NiAPSO-34, the nickel ion is possibly also coordinated to additional waters to give distorted octahedral coordination. On dehydration, tetrahedrally coordinated nickel in a framework site of SAPO-34 is formed.

Tailored crystalline microporous materials by post-synthesis modification

“…324 The introduction of In 3+ , Ga 3+ , Cu 2+ , and Ni 2+ into SAPO-34 by preparing a mechanical mixture of Me 2 O 3 oxide and SAPOtype material was reported. [325][326][327][328] The H-form of SAPO-34 was used, which after mixing with the metal was subjected to reduction in a H 2 atmosphere. The solid state reaction led to the replacement of proton sites in SAPO-34 with Me + cations and thus to modification of the catalytic properties.…”

Incorporation of mixed metals into SAPO-34 frameworks by the dry-gel conversion method using mixed templates: investigating catalysts characterisation and performance

“…For example, some investigations have reported significantly higher ethylene selectivity for NiAPSO-34; [7] while other investigations have reported NiAPSO-34 leads to less production of ethylene. [8] A different synthetic method, namely dry-gel conversion (DGC), was introduced a few years ago as an alternative to hydrothermal synthesis (HTS) method. [9] In this method, before crystallisation the initial gel is dried up at elevated temperature and atmospheric pressure.…”

Removal of Carbon Dioxide from Light Gas Mixtures using a Porous Strontium(II) Silicoaluminophosphate Fixed Bed: Closed Volume and Portable Applications

“…SAPO-34 is a crystalline porous material with the framework characteristics of the natural zeolite Chabazite and, like all SAPOs, is formed by tetrahedrally coordinated silicon, aluminum, phosphorus, and oxygen atoms. These SAPO frameworks hold a net charge (+1, −1, or 0) that depends on the substitution of silicon for phosphorus or aluminum (20)(21)(22), and therefore may require extraframework species to counterbalance the framework 490 Downloaded by [University of Waterloo] at 11:08 20 November 2014 charge. Since silicon usually substitutes for phosphorus (20), the SAPO-34 framework requires extra-framework cations.…”

“…These SAPO frameworks hold a net charge (+1, −1, or 0) that depends on the substitution of silicon for phosphorus or aluminum (20)(21)(22), and therefore may require extraframework species to counterbalance the framework 490 Downloaded by [University of Waterloo] at 11:08 20 November 2014 charge. Since silicon usually substitutes for phosphorus (20), the SAPO-34 framework requires extra-framework cations. These species, mostly Na + and H + in SAPO-34, are products of the hydrothermal synthesis and calcination of the structure directing-agent and can be readily exchanged by other metal cations, changing the net electronic charge and atomic radii, and therefore, affecting the field-gradient quadrupole contribution to the total adsorption energy (2).…”