Pt/TiH₂ Catalyst for Ionic Hydrogenation via Stored Hydrides in the Presence of Gaseous H₂

Abstract

A Pt/TiH2 catalyst having hydrogen storage and release capability was investigated for selective hydrogenation of trans-cinnamaldehyde (CAL) to cinnamyl alcohol (COL) with gaseous dihydrogen. The catalytic behavior of this catalyst was significantly different from that of a reference Pt/TiO2 catalyst with respect to the product selectivity and the hydrogenation mechanism. The Pt/TiH2 catalyst showed a COL selectivity of 97% at a CAL conversion of 98%, which was ascribed to the function of a Pt crystallite–support boundary layer that caused the preferential adsorption of CAL with its carbonyl group. Furthermore, the carbonyl group was hydrogenated by hydride species (H+, H–) supplied from the support and the hydride species consumed were compensated from gaseous dihydrogen; hydrogen atoms were formed by ordinary homolytic cleavage on Pt and then these hydrogen atoms moved onto the surface of TiH2 and diffused into the bulk of the support, during which those simultaneously changed to hydride species (H+, H–) via electron transfer with titanium species and hydride vacancies therein. The surface and bulk diffusion of the hydrogen atoms from Pt to TiH2 support should be the dominant step rather than their addition to the carbonyl group of CAL (ordinary hydrogenation). That is, ionic hydrogenation occurs with Pt/TiH2 in the presence of gaseous dihydrogen.

Identification and Insight into the Role of Ultrathin LDH‐Induced Dual‐Interface Sites for Selective Cinnamaldehyde Hydrogenation

“…Then, in order to measure the chemical adsorption, the gaseous and physically adsorbed cinnamaldehyde is removed by He flow purging. For the bulk catalyst (Figure 8A(a)), the bands at 1671 and 1630 cm −1 are assigned to ν (C=O) and ν (C=C) adjacent to C=O in CAL coordinated on the catalyst, which represents the CAL is adsorbed on the catalyst in the di‐σ CO adsorption mode [2,42] . However, as for ultrathin Pt/CoAl‐LDH catalyst (Figure 8A(b)), both ν (C=O) and ν (C=C) bands show a significantly red shift, moving to 1664 cm −1 and 1621 cm −1 , respectively.…”

“…As shown in Figure 5B, the ultrathin catalyst can keep the CAL conversion and selectivity towards COL at >90 % and >90 % within 6 cycles, respectively, which is much higher than those of the fresh bulk catalyst. More importantly, in comparison with some representative reported CAL selective hydrogenation catalysts, the ultrathin Pt/CoAl‐LDH catalyst in this work exhibits a significant advantage in both intrinsic activity and selectivity towards COL, which is listed in Table S1 [1,6,41–45] …”

A Cationic Ru(II) Complex Intercalated into Zirconium Phosphate Layers Catalyzes Selective Hydrogenation via Heterolytic Hydrogen Activation

“…Acetophenone derivatives containing -R or -OR groups were tested with longer reaction time (10 h), and the conversions were relatively lower than that of acetophenone (Table 3, entry 4-8). The electron donating groups (À R and À OR) reduced the reactivity of C=O in these substrates likely due to the heterolytic activation of H 2 , [70] which weakened the attack of H À to the C atom. Besides, the hydrogenation of cinnamaldehyde and bio-derived platform molecules, including 5-hydroxymethyl-furfural (HMF), also afforded the corresponding alcohol with good selectivity under a slightly higher hydrogenation pressure (2.0 MPa) (Table 3, entry 9).…”

Highly Selective Catalysis at the Liquid–Liquid Interface Microregion

“…This transformation is always known as a challenging reaction because the desired hydrogenation of the C=O bond is, however, thermodynamically and kinetically unfavorable over the C=C bond 3,4 . To improve the selectivity to the C=O hydrogenation, several catalysts have been developed such as organic molecule-modi ed metal nanoparticles [5][6][7] , metal-supported catalysts [8][9][10][11][12] , bimetallic catalysts [13][14][15] and organometallic catalysts 16 . Despite state-of-the-art progress made and cutting-edge catalysis knowledge obtained, these methods of selectivity regulation are largely limited to the tuning of electronic state and structure of catalysts.…”