# Role of Ion-Exchange Resins in Hydrogen Reactions
## 3 Ion-Exchange Resins Application to Hydrogenation Reactions
### Other Related Reactions  
With regards to the role of IERs in other hydrogenation reactions (or related reaction systems), the direct synthesis of hydrogen peroxide from molecular oxygen and hydrogen stands out as one of the most studied processes. For instance, [PERSON] and coworkers successfully prepared bimetallic Pd-Au (Pd: 1.0; Au: 0.25-1.0 wt.%) and Pd-Pt (Pd: 1.0; Pt: 0.1-1.0 wt.%) catalysts over a commercial, ST-DVB macroreticular resin, Lewatit\({}^{\text{\textregistered}}\) K2621, by simple ion-exchange in water and reduction with aqueous formaldehyde, which they tested in the direct synthesis of hydrogen peroxide [58]. They found that the presence of small amounts of either Pt or Au in Pd catalysts promoted selectivity while reducing activity in comparison with monometallic Pd catalysts, but that further addition of Pt or Au produced different effects: while activity increases with an increasing amount of Au, a maximum in hydrogen peroxide productivity was observed with 0.5 wt.% Pt addition, but also the lowest selectivity level was achieved. Other relevant examples of works dealing with this reaction system are those by [PERSON] (2006) and [PERSON] (2019), which have already been commented on in previous sections [52; 66]. Concerning catalytic hydrodechlorination reactions, [PERSON] et al. (2014) supported Pd and Pt over DowexTM 1 \(\times\) 4, an ST-DVB gel-type resin, functionalized with trimethylammonium, and the catalysts were tested in the hydrogenation of chloronitrobenzene isomers into the corresponding chloronanilines. The resin was used either in the chloride form or in the OH\({}^{-}\) form, and about 1 wt.% metal contents were measured. From ISEC analyses before and after metal deposition, it became evident that lower concentrated polymer domains (i.e., 0.4 mmm\({}^{-3}\)) decreased with the metal incorporation while increasing higher concentrated domains (0.8 mmm\({}^{-3}\)) [120]. Regarding the catalytic results, _x_-chloronitrobenzene, _x_-chloroaniline, aniline, _x_-chloronitrobenzene, and nitrobenzene were detected in the reaction medium after the catalytic tests, with _x_-chloroeniline being the target product in that work (i.e., reduction of the NO\({}_{2}\) group, without hydrodechlorination). Significantly higher activity, but lower selectivity to _x_-chloroaniline, was found for the Pd-containing catalysts in the OH\({}^{-}\) form than for their chloride counterparts. As indicated by the authors, in previous works by [PERSON] et al. (2002, 2003), where a Pd-doped, ST-DVB sulfonated IER was compared to Pd/charcoal catalyst and the effect of different solvents was evaluated, it had already been established that condensation reactions occurring in basic environments lowered the selectivity to _x_-chloroaniline [121; 122]. All Pt catalysts in [PERSON] et al. (2014) were more active than the Pd ones, which the authors linked to the lower average size of Pt crystallites (2.3 nm) in comparison with the Pd ones (4.5 nm) [120]. [PERSON] and coworkers used AmberliteTM IRA-900 and IRA-958 (both in Cl\({}^{-}\) form) as support for Pd (0.1-11.2 wt.%, 3-5 nm) to catalyze the complete hydrodechlorination of triclosan (5-chloro-2-(2,4-dichlorophenoxyoxy)phenol). Both resins are of the macroreticular type with quaternary amine as the functional group, but IRA-900 is an ST-DVB resin whereas IRA-958 is acrylic. IRA-958 showed better performance than IRA-900, which was attributed to the hydrophobicity, pore size, and surface area of its polymeric matrix, and to larger Pd particle size (4.6 and 3.7 nm for IRA-958 and IRA-900, respectively, but with some larger aggregates of 20-40 nm diameter range observed on IRA-958). Both catalysts were reused multiple times without significant loss in effectivity or leaching [123]. On the other hand, [PERSON] et al.