# Role of Ion-Exchange Resins in Hydrogen Reactions
## 1 Introduction
Typically, resins are thermally stable at temperatures up to 120-135 \({}^{\circ}\)C, but IERs exist with a higher thermal resistance that are able to operate at 170-190 \({}^{\circ}\)C (e.g., Amberlyst\({}^{\text{TM}}\) 45, Amberlyst\({}^{\text{TM}}\) DT, Purolite\({}^{\text{\textregistered}}\) CT482) [34; 35]. Two main types of IERs are distinguished, based on their porosity: gel-type resins and macroreticular resins. Gel-type resins present a microporous, collapsed structure in a dry state that swells in contact with a polar solvent, such as water or certain alcohols, exhibiting thereby considerable porosity [36]. This type of resin can be obtained by free-radical crosslinking copolymerization of, for instance, styrene (ST) and divinylbenzene (DVB) monomers through suspension polymerization [33]. Macroreticular resins are composed of agglomerates of gel-type zones, with their respective polarity-sensitive microporous structure, that have a permanent macroporous structure in the dry state [33; 36]. Macroreticular \begin{table}
\begin{tabular}{c c c} \hline \hline
**Author(s)** & **Topic Reviewed** & \multicolumn{2}{c}{**Date to Which the Literature is Covered**} \\ \hline [PERSON] and [PERSON] [8] & Dispersion of metal nanoclusters inside IER & 2000 \\ [PERSON] and [PERSON] [9] & Generation of Pd nanoclusters inside IER & 2000 \\ [PERSON] and [PERSON] [24] & Catalysis by metal nanoparticles supported on functional organic polymers & 2001 \\ [PERSON] et al. [25] & IER as support for metal catalysts & 2003 \\ [PERSON] [4] & IER applications as catalysts for organic syntheses & 2005 \\ [PERSON] et al. [10] & Immobilization of catalysts on polymeric supports & 2006 \\ [PERSON] and [PERSON] [26] & Applications of IER as catalysts, including hydrogations & 2008 \\ [PERSON] et al. [27] & Synthesis and catalytic activity evaluation of metal nanoclusters inside IER & 2009 \\ [PERSON] et al. [28] & Synthesis, characterization, and applications of polymer-supported metals & 2011 \\ [PERSON] et al. [29] & Bifunctional metal/acid catalysts for one-pot processes involving hydrogenation & 2012 \\ [PERSON] et al. [29] & and hydrolysis, lactonization, esterification, or cyclization, among others & 2012 \\ [PERSON] et al. [12] & Conversion of biomass platform molecules into fuel additives & 2013 \\ [PERSON] et al. [30] & Metal nanoparticles immobilized on IER as catalysts for sustainable chemistry & 2015 \\ [PERSON] and [PERSON] [13] & Application of IER and other polymeric materials in hydrogenation reactions & 2017 \\ [PERSON] and [PERSON] [14] & Application of IER and other polymeric materials in esterification, & 2019 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Previous review papers related to the use of IERs in hydrogenation reactions. resins can be synthesized by suspension polymerization of an ST-DVB monomer mixture in the presence of a diluent, which acts as a porogen that gives rise to the formation of a permanent porous structure within the highly crosslinked polymer particles upon its extraction. Functionalization of the resins is usually achieved by chemical modification of an already-formed copolymer matrix [33; 36; 37; 38; 23]. For instance, the acidic character of sulfonic IERs is usually achieved by direct contact with concentrated sulfuric acid between 303 and 413 K [39; 40; 36]. Among the wide range of IERs applications--including water softening and purification, demineralization, chromatography, pharmaceutical formulations, agricultural or mining, among others--their use as catalysts or catalyst supports has been well-known and appreciated for decades since they represent a conveniently cost-effective option for many industrial applications--e.g., alkylation, hydration, dehydration, etherification, esterification, condensation, cyclization, hydrolysis, oligomerization, C-C coupling, oxidation or hydrogenation reactions [3; 13].