Proton transfer across single-layer graphene proceeds with large computed energy barriers and is therefore thought to be unfavourable at room temperature unless nanoscale holes or dopants are introduced, or a potential bias is applied. Here we subject single-layer graphene supported on fused silica to cycles of high and low pH, and show that protons transfer reversibly from the aqueous phase through the graphene to the other side where they undergo acid–base chemistry with the silica hydroxyl groups. After ruling out diffusion through macroscopic pinholes, the protons are found to transfer through rare, naturally occurring atomic defects. Computer simulations reveal low energy barriers of 0.61–0.75 eV for aqueous proton transfer across hydroxyl-terminated atomic defects that participate in a Grotthuss-type relay, while pyrylium-like ether terminations shut down proton exchange. Unfavourable energy barriers to helium and hydrogen transfer indicate the process is selective for aqueous protons.

Increases in the cost of petroleum combined with growing concerns for CO 2 emissions are prompting researchers worldwide to search for renewable sources of liquid fuel. In this respect, biomass is currently the only sustainable source of organic carbon, and biofuels are currently the only sustainable source of liquid fuels. [1] The challenge with biomass conversion into liquid fuels is that efficient processes are not yet economically viable.A large number of processes for converting biomass into biofuels involve hydrogenation of biomass-derived feedstock in the aqueous phase. These include hydrogenation of biooils, [2,3] hydrogenation of fermentation broths, [4] and alkane production by aqueous phase processing. [5,6] Hydrogenation of organic acids, which are produced in fermentation, results in a 50 % increase in ethanol yield compared to when ethanol is produced directly from fermentation. [7] Upgrading bio-oils by hydrotreating involves hydrogenating a range of functional groups, which also include organic acids. In fact, one of the slowest steps in the hydrotreating of bio-oils is the hydrogenation of organic acids. [3] For these hydrotreating routes to become economically viable, it is critical to design highly active and selective catalysts for aqueous-phase hydrogenation (APH) reactions. So far there has been no systematic study for the APH of acetic acid on monometallic catalysts.Herein we report the findings of a combined experimental and theoretical study on the APH of acetic acid catalyzed by transition metals such as Ru, Rh, Pd, Ni, Cu, Ir, and Pt. Significantly different activities for the conversion of acetic acid have been observed over these metals. High selectivities for ethanol were obtained for several of them; in particular, Ru showed approximately 80 % ethanol selectivity at moderate temperatures. Density functional theory (DFT) calculations suggested that the different activity can be attributed to the intrinsic reactivity of the metals for dissociating acetic acid or acetate to acetyl (CH 3 O), and a simple empirical correlation is identified that may be used to readily estimate the free energy of the transition state (TS) for the rate-limiting step in acetic acid conversion based on the adsorption energies of acetyl and hydroxy groups. These findings offer clues for designing [8][9][10] active and selective transition metal catalysts for the hydrogenation of organic acids and oxygenates in general.The activity of the APH of acetic acid has been measured for Ru/C, Pt/C, Pd/C, Rh/C, Ir/Al 2 O 3 , Raney Ni, and Raney Cu catalysts at temperatures from 110-290 8C, and at 5.17 MPa total pressure. The catalytic activity of each catalyst was measured at acetic acid conversion of less than 25 % in the absence of diffusion limitations (see the Supporting Information for Weisz modulus calculations). Figure 1 shows the turnover frequencies (TOFs) as a function of temperature for the total conversion of acetic acid. The TOFs of acetic acid conversion decrease in the order Ru > Rh % Pt > Pd % Ir > Ni >...

The adaptive kinetic Monte Carlo method uses minimum-mode following saddle point searches and harmonic transition state theory to model rare-event, state-to-state dynamics in chemical and material systems. The dynamical events can be complex, involve many atoms, and are not constrained to a grid-relaxing many of the limitations of regular kinetic Monte Carlo. By focusing on low energy processes and asserting a minimum probability of finding any saddle, a confidence level is used to describe the completeness of the calculated event table for each state visited. This confidence level provides a dynamic criterion to decide when sufficient saddle point searches have been completed. The method has been made efficient enough to work with forces and energies from density functional theory calculations. Finding saddle points in parallel reduces the simulation time when many computers are available. Even more important is the recycling of calculated reaction mechanisms from previous states along the dynamics. For systems with localized reactions, the work required to update the event table from state to state does not increase with system size. When the reaction barriers are high with respect to the thermal energy, first-principles simulations over long time scales are possible.

The small and synthetically easily accessible 7-diethylamino-4-thiocoumarinylmethyl photolabile protecting group has been validated for uncaging with blue light. It exhibits a significant action cross-section for uncaging in the 470-500 nm wavelength range and a low light absorption between 350 and 400 nm. These attractive features have been implemented in living zebrafish embryos to perform chromatic orthogonal photoactivation of two biologically active species controlling biological development with UV and blue-cyan light sources, respectively.