# Role of Ion-Exchange Resins in Hydrogen Reactions
## 3 Ion-Exchange Resins Application to Hydrogenation Reactions
### One-Pot Multistep Reaction Processes Involving Hydrogenation  
Regarding multistep processes, several relevant examples can be found in the literature, signaling that this specific field is of great interest since it deals directly with the integration and optimization of processes enabling the one-pot synthesis of valuable chemicals. For instance, the simultaneous hydrogenation and isomerization of disobutylenes (2,4,4-trimethylpent-1-ene, TMP1, and 2,4,4-trimethylpent-2-ene, TMP2) over a Pd-doped IER was investigated by [PERSON] and coworkers [102]. Interestingly, the commercial Amberlyst(tm) CH28 bifunctional catalyst, which contains Pd nanoparticles and -SO\({}_{3}\)H functional groups in a macroreticular matrix, was found to favor isomerization of TMP2 to TMP1, which is more prone to hydrogenation towards isooctane than TMP2 due to the terminal position of the double bond. From this, it follows that bifunctionalization of a resin with acid and metallic groups can offer selectivity changes in isomerization reactions, making the subsequent hydrogenation step more profitable. The effects of operating parameters (i.e., temperature, catalyst loading, hydrogen pressure, impurities associated with TMPs, and catalyst reusability) were evaluated and a kinetic model was proposed. [PERSON] et al. (2007, 2008) reported on the one-pot synthesis of 2-ethylhexanal from crotonaldehyde, which involves hydrogenation and aldol condensation in supercritical CO\({}_{2}\), over a bifunctional acidic resin-supported palladium catalyst [83; 103]. They incorporated Pd (1 wt.%) onto Amberlyst(tm) 15 and obtained 13-98% conversions and \(\sim\)0-67% selectivity values, depending on the assayed conditions. The one-pot synthesis of a potential analgesic over Pd/Amberlyst(tm) 15 was studied by [PERSON] and coworkers. In their work, two reaction steps are involved: dehydration of the starting tertiary alcohol, followed by hydrogenation of the obtained olefin. At the proposed optimized conditions, the reported conversion was 98%, and the selectivity towards the target product was 64%. However, prompt deactivation of the catalyst in the first reuse was observed, which the authors link to possible coke formation on the resin, since they argue that the selected temperature (i.e., 150 \({}^{\circ}\)C) is not high enough to promote thermal instability and no Pd leaching was observed [104]. Besides the examples mentioned so far, the specific, yet broad, field of biomass transformation into high-value-added products seems to be particularly suited for using metal-doped IER. For instance, [PERSON] et al. (2016) focused on the direct conversion of glucose and xylose to isosorbide and anhydroxylitol, respectively, involving hydrogenation followed by dehydration. Dowex(tm) 50W \(\times\) 2 in its H\({}^{+}\) form was used as support for Ru, with reported yields of 84.9% for isosorbide and 94.9% for anhydroxylitol at 190 \({}^{\circ}\)C with 30 bar H\({}_{2}\) in water in batch experiments [94]. Such high yields are attributed to a combined effect of (i) a favorable microporous structure of IER and a narrow size distribution of Runanoparticles, which would enhance hydrogenation selectivity, and, (ii) a proper balance of density and strength of Bronsted acid sites, which would enhance dehydration. In a different approach, a mixture of Pt/C catalyst and the thermostable, ST-DVB macroticular resin AmberlystTM 70 was used for the cellulose conversion into isosorbide, which involves three consecutive reaction steps: hydration, hydrogenation, and dehydration [105]. The same approach was adopted in [PERSON] et al. (2012) for the synthesis of \(\gamma\)-valerolactone (GVL) from levulinic acid [106]. With respect to GVL production, Au, Pt, Ir, Ni, Cu, Re, Rh, and Ru over different supports have been mentioned as effective catalysts to obtain GVL by hydrogenation of levulinic acid [95; 107; 108; 109; 110; 111]. In this process, either hydrogenation followed by dehydration or dehydration-hydrogenation reactions take place.