# Role of Ion-Exchange Resins in Hydrogen Reactions
## 3 Ion-Exchange Resins Application to Hydrogenation Reactions
### Hydrogenation of Nitrates  
The aqueous catalytic reduction of nitrates to molecular nitrogen with hydrogen was studied by [PERSON] and coworkers (2006, 2007) over bimetallic Pd-Cu catalysts (4 wt.% Pd, 1 wt.% Cu) supported on DowestTM 1 \(\times\) 4 in the chloride form ([PERSON] et al., 2016; [PERSON] et al., 2016). DowestTM 1 \(\times\) 4 is a gel-type ST-DVB resin functionalized with -N(CH3)3+ groups. In the first study, five reduction protocols were adopted (C1: NaBH4 in ethanol; C2: NaBH4 in water; C3: 0.1 MPa H2, Na2 CO3 in H2O; C4: 0.5 MPa H2, Na2 CO3 in H2O; and C5: 0.5 MPa H2, Na2 CO3 in methanol) and results were compared. Distinct Pd nanoparticles sizes were observed for each reduction protocol, with C1 being undetectable (which suggests either an amorphous metal phase or with very small particles), C2 presenting the largest particles (i.e., 6.7 nm), and C5 the smallest size (i.e., 2.9 nm). As for the catalytic outcome, the highest selectivity to N2 was achieved by C1 (96%) at 71% nitrates conversion but with the largest Cu leaching detected. Overall, the best catalyst, according to the authors, was C5 since it yielded 73% conversion, with 77% selectivity towards N2, and the lowest Cu leaching. For all catalysts, Pd leaching was below detection limits ([PERSON] et al., 2016). In [PERSON] et al. (2007), the Pd-Cu/DowestTM catalyst was compared to Pd-Cu/Al2O3. Two reduction protocols were applied to either type of catalyst. For the resin-based catalyst, the protocols were as follows: H2 in 2.5% water solution of Na2 CO3 for 1 h at 25 \({}^{\circ}\)C and 0.5 MPa (cataly 1), or 0.066 M solution of NaBH4 in ethanol for 1 h at ambient temperature under occasional stirring (cataly 2). Interestingly, catalyst 2 presented a very homogeneous distribution of Pd and Cu, with Pd- and Cu-containing phases too small to be detected by XRPD, or amorphous, whereas Pd and Cu were mainly located in a shallow external layer of catalyst 1, with Pd nanoparticles of 3.8 nm. This suggests a clear effect of the reduction protocol in the metal distribution within the resin beads. Noticeably, expected byproducts, namely nitrites (produced by partial reduction) and ammonia (over reduction), were almost avoided with resin-based catalysts (i.e., selectivity towards N2 was 93.8% at 44% conversion with catalyst 2). On the other hand, Pd-Cu/Al2O3 catalysts were more active, yet less selective to N2 (below 60%) than resin catalysts. Furthermore, while Pd-Cu/Al2O3 catalysts showed some leaching of Cu (no leaching of Pd was detected), Cu and Pd in solution were below detection limits for resin-based catalysts ([PERSON] et al., 2016). Another Pd-Cu catalyst was investigated by [PERSON] and coworkers for the same reaction system, with the emphasis being made on the performance of two processes for nitrates removal ([PERSON] et al., 2016). In their work, [PERSON] used a macroporous, ST-DVB anion exchange resin (i.e., DiaionTM WA30), containing tertiary amine functional groups. Pd incorporation in the resin was accomplished by contact with PdCl2 solution dissolved in NaCl 0.01 M and HCl 0.01 M while bubbling N2. After reduction of the PdII to Pd0 with 35 wt.% hydrazine solution, Cu was incorporated by means of the controlled surface reduction method. In this procedure, the reduced Pd/WA30 catalyst was suspended in water and H2 was bubbled for 2 h; then, a CuNO3:3H2O solution was added while maintaining the hydrogen bubbling for 2 h. After several additional steps involving filtration, reduction, and washing operations, the final metal contents were 2 wt.% Pdand 0.5 wt.% Cu, as verified by energy-dispersive X-ray fluorescence (XRF). Depending on the operating conditions, conversion, and selectivity to N\({}_{2}\) values as high as 100% are reported [100].