02711nas a2200301   4500008004100000022001400041245013500055210006900190260000900259300001100268490000800279520168000287653001801967653003001985653002802015653002402043653001602067653002002083100002802103700001902131700001902150700002102169700002302190700002602213700001602239700002502255856012902280       2026                        eng d  a2468-823100aEffect of sulfonation density on acid strength in ion exchange resins: Insights from solid-state NMR and density functional theory0 aEffect of sulfonation density on acid strength in ion exchange r  cMAR   a1157940 v5933 a<p>
	Ion-exchange (IE) resins are widely used as solid acid catalysts; however, their surface acidity remains poorly characterized because their limited thermal stability precludes conventional NH3-based acidity measurements. Moreover, acid-site accessibility in IE resins is strongly governed by solvent- or reactant-induced swelling. Here, we investigate the surface acidity of commercial Amberlyst and Indion IE resins using &amp; sup3;&amp; sup1;P MAS NMR (Magic Angle Spinning Nuclear Magnetic Resonance), employing TMPO as a molecular probe dispersed on the resin with moderately swelling dichloromethane, thereby capturing the swollen-state acidity relevant for predicting catalytic activity. The deconvolution of the P-31 MAS NMR spectra reveals three distinct acid-strength zones arising from inhomogeneous sulfonation of the polymer matrix. The overall acidity, quantified by the area-weighted average P-31 chemical shift (delta), increases monotonically with sulfonation density. Notably, only resins containing acid sites stronger than similar to 80 ppm exhibited measurable catalytic activity in alpha-pinene isomerization, establishing a direct correlation between acidity and activity. Density functional theory (DFT) calculations on representative resin models, supported by electron-density analyses, attribute the enhancement of acid strength at higher sulfonation densities to cooperative hydrogen-bonding networks among neighboring sulfonic acid groups. Together, these findings establish P-31 MAS NMR-derived surface acidity as a catalytically relevant descriptor for the rational selection of IE resins in liquid phase acid-catalyzed chemistries.</p>
10aAcid strength10aDensity functional theory10aheterogeneous catalysis10aIon-exchange resins10aSolid acids10aSolid-state NMR1 aTumulu, Goutam, Narayan1 aDatar, Sarvesh1 aShelke, Ankita1 aSwain, Gitanjali1 aAjithkumar, T., G.1 aThirumalaiswamy, Raja1 aMohan, Ojus1 aMahajani, Sanjay, M.  uhttps://library.ncl.res.in/content/effect-sulfonation-density-acid-strength-ion-exchange-resins-insights-solid-state-nmr-and