<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Tumulu, Goutam Narayan</style></author><author><style face="normal" font="default" size="100%">Datar, Sarvesh</style></author><author><style face="normal" font="default" size="100%">Shelke, Ankita</style></author><author><style face="normal" font="default" size="100%">Swain, Gitanjali</style></author><author><style face="normal" font="default" size="100%">Ajithkumar, T. G.</style></author><author><style face="normal" font="default" size="100%">Thirumalaiswamy, Raja</style></author><author><style face="normal" font="default" size="100%">Mohan, Ojus</style></author><author><style face="normal" font="default" size="100%">Mahajani, Sanjay M.</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Effect of sulfonation density on acid strength in ion exchange resins: Insights from solid-state NMR and density functional theory</style></title><secondary-title><style face="normal" font="default" size="100%">Molecular Catalysis</style></secondary-title></titles><keywords><keyword><style  face="normal" font="default" size="100%">Acid strength</style></keyword><keyword><style  face="normal" font="default" size="100%">Density functional theory</style></keyword><keyword><style  face="normal" font="default" size="100%">heterogeneous catalysis</style></keyword><keyword><style  face="normal" font="default" size="100%">Ion-exchange resins</style></keyword><keyword><style  face="normal" font="default" size="100%">Solid acids</style></keyword><keyword><style  face="normal" font="default" size="100%">Solid-state NMR</style></keyword></keywords><dates><year><style  face="normal" font="default" size="100%">2026</style></year><pub-dates><date><style  face="normal" font="default" size="100%">MAR </style></date></pub-dates></dates><volume><style face="normal" font="default" size="100%">593</style></volume><pages><style face="normal" font="default" size="100%">115794</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">&lt;p&gt;
	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;amp; sup3;&amp;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.&lt;/p&gt;
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	Foreign&lt;/p&gt;
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	4.9&lt;/p&gt;
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