Hydrogenomics: Efficient and Selective Hydrogenation of Stable Molecules Utilizing Three Aspects of Hydrogen

Pressure-Induced Dehydration and Reversible Recrystallization of Dihydrogen-Bonded Sodium Borohydride Dihydrate NaBH4·2H2O

Sodium borohydride dihydrate (NaBH4·2H2O) forms through dihydrogen bonding between the hydridic hydrogen of the BH4- ion and the protonic hydrogen of the water molecule. High-pressure structural changes in NaBH4·2H2O, observed up to 11 GPa through X-ray diffraction and Raman scattering spectroscopy, were analyzed to assess the influence of dihydrogen bonds on its crystal structure. At approximately 4.6 GPa, certain dihydrogen bonds were broken, leading to the decomposition of NaBH4·2H2O into ambient pressure phase of NaBH4 (α-NaBH4) and ice VII. Upon further compression beyond 6.6 GPa, NaBH4 gradually transformed into its high-pressure phase, γ-NaBH4. During decompression, γ-NaBH4 reverted to α-NaBH4 at the pressure between 4.4 and 2.7 GPa and subsequently reacted with ice VII, resulting in the recrystallization of NaBH4·2H2O. This recrystallization, occurring during decompression from 4.4 to 2.7 GPa, is identical to the starting sample and can be termed "decompression-induced recrystallization", highlighting the strength of the dihydrogen bonds in NaBH4·2H2O. In addition, density functional theory calculations were used to evaluate the pressure dependence of hydrogen-hydrogen (H-H) distances in NaBH4·2H2O. As pressure increased, the number of dihydrogen bonds within the unit cell rose from seven at near-ambient pressure to 12 at approximately 4.5 GPa just before the dehydration, indicating that each hydrogen atom in the water molecule formed dihydrogen bonds with around three hydrogens from the BH4- ions just prior to dehydration. Such pressure tuning of dihydrogen bonds may lead to the creation of new energy storage materials.

Propane dehydrogenation catalysis of group IIIB and IVB metal hydrides

Catalytic propane dehydrogenation (PDH) has mainly been studied using metal- and metal oxide-based catalysts. Studies on dehydrogenation catalysis by metal hydrides, however, have rarely been reported. In this study, PDH reactions using group IIIB and IVB metal hydride catalysts were investigated under relatively low-temperature conditions of 450 °C. Lanthanum hydride exhibited the lowest activation energy for dehydrogenation and the highest propylene yield. Based on kinetics studies, a comparison between the reported calculation results and isotope experiments, the hydrogen vacancies of metal hydrides were involved in low-temperature PDH reactions.

Phase Diagram Analysis of High-Pressure/High-Temperature Polymorphs of Ammonia Borane

Ammonia borane (NH3BH3) is a promising hydrogen-storage material because of its high hydrogen density. It is employed as a hydrogen source when synthesizing superconducting polyhydrides under high pressure. Additionally, NH3BH3 is a crystallographically interesting compound that features protonic hydrogen (Hδ+) and hydridic hydrogen (Hδ-), and it forms a dihydrogen bond, which explains its stable existence as a solid. Herein, X-ray diffraction experiments were performed at high pressures (HPs) and high temperatures (HTs) of up to 30 GPa and 300 °C, respectively, to investigate the HP/HT phase diagram of NH3BH3. A new HP/HT phase (HPHT2) was identified above 9 GPa and 150 °C. Crystal-structure analysis using the Rietveld method and stability verification using density functional theory calculations revealed that HPHT2 has a P21/n (Z = 4) structure, similar to that of a previously reported HP/HT phase (HPHT) that appears at a lower pressure. HPHT2 is denser than the HP phases that appear at room temperature (HP1 and HP2) at the same pressure (up to ∼17 GPa). In the phase diagram, the phase-boundary line between HPHT and HP1 is a downward convex curve. These unconventional phenomena in the density and phase boundary can be attributed to the influence of dihydrogen bonding on the crystal structure and phase diagram.

Cu Modified TiO2 Catalyst for Electrochemical Reduction of Carbon Dioxide to Methane

Electrochemical reduction of CO2 (ECO2R) is gaining attention as a promising approach to store excess or intermittent electricity generated from renewable energies in the form of valuable chemicals such as CO, HCOOH, CH4, and so on. Selective ECO2R to CH4 is a challenging target because the rate-determining step of CH4 formation, namely CO* protonation, competes with hydrogen evolution reaction and the C–C coupling toward the production of longer-chain chemicals. Herein, a Cu-TiO2 composite catalyst consisting of CuOx clusters or Cu nanoparticles (CuNPs), which are isolated on the TiO2 grain surface, was synthesized using a one-pot solvothermal method and subsequent thermal treatment. The Cu-TiO2 catalyst exhibited high selectivity for CH4, and the ratio of FE for CH4 to total FE for all products in ECO2R reached 70%.

Elucidation of the atomic-scale processes of dissociative adsorption and spillover of hydrogen on the single atom alloy catalyst Pd/Cu(111)

Hydrogen spillover is a crucial process in the selective hydrogenation reactions on Pd/Cu single atom alloy catalysts. In this study, we report the atomic-scale perspective of these processes on the...

Selectivity enhancement in the electrochemical reduction of oxalic acid over titanium dioxide nanoparticles achieved by shape and energy-state control

The morphology of TiO2 nanoparticles has a substantial impact on the product selectivity in an electrochemical reduction reaction.