Sustainable Hydrogen from Bio-Oil - Catalytic Steam Reforming of Acetic Acid as a Model Oxygenate

Studies were conducted with acetic acid (HAc) as model oxygenate for the design of active and stable catalysts for steam reforming of bio-oil. Pt/ZrO2 catalysts were prepared by wet impregnation technique. The Pt/ZrO2 catalysts showed high activities at initial time on stream, but lost its activity for steam reforming (H2 production) rapidly. During HAc/H2O reaction over Pt/ZrO2, conversion was close to 100% and constant for 3 hr, however, yields of products changed with time. In the beginning (5 min), H2 and CO2 were the main products, CH4 and CO were observed in small quantities. During HAc/H2O reaction over ZrO2 (without Pt), HAc conversion was close to 90%. The conversion of HAc and yields of the products were constant for 3 hr. However, no steam reforming activity (H2 and CO) was observed, and only acetone and CO2 were observed as products. Both Pt/ZrO2 and ZrO2 were very active for HAc conversion. However, H2 and CO, i.e., steam reforming products, were produced only over Pt/ZrO2 and not over ZrO2. ZrO2 showed acetone yields similar to those observed over Pt/ZrO2 after 25 min time on stream. The presence of acetone in the product mixture and formation of deposits on ZrO2 indicated a role for acetone in catalyst deactivation

Catalyst deactivation during steam reforming of acetic acid over Pt/ZrO2.

Steam reforming of acetic acid as a model compound present in bio-oil over Pt/ZrO2 catalysts has been investigated. Pt/ZrO2 yields steam reforming products (i.e., H2, CO, CO2) to the amounts predicted by thermodynamic equilibrium; however, conversion and yields dropped rapidly with time on course. The deactivation was due to blockage of active sites by coke/oligomer formed. This report clarifies cause of the deactivation during steam reforming of acetic acid. It was found that many products can be formed from acetic acid on ZrO2, such as acetone. The experimental results confirmed that aldol condensation of acetone took place on ZrO2 to give larger compounds which can easily become deposits to block active sites for steam reforming. In order to develop durable catalysts for steam reforming of bio-oil, support should be designed to enhance activation of water, minimize dehydration reactions and thus oligomer formation

Poly(3-hydroxybutyrate) production in an integrated electromicrobial setup: Investigation under stress-inducing conditions

Poly(3-hydroxybutyrate) (PHB), a biodegradable polymer, can be produced by different microorganisms. The PHB belongs to the family of polyhydroxyalkanoate (PHA) that mostly accumulates as a granule in the cytoplasm of microorganisms to store carbon and energy. In this study, we established an integrated one-pot electromicrobial setup in which carbon dioxide is reduced to formate electrochemically, followed by sequential microbial conversion into PHB, using the two model strains, Methylobacterium extorquens AM1 and Cupriavidus necator H16. This setup allows to investigate the influence of different stress conditions, such as coexisting electrolysis, relatively high salinity, nutrient limitation, and starvation, on the production of PHB. The overall PHB production efficiency was analyzed in reasonably short reaction cycles typically as short as 8 h. As a result, the PHB formation was detected with C. necator H16 as a biocatalyst only when the electrolysis was operated in the same solution. The specificity of the source of PHB production is discussed, such as salinity, electricity, concurrent hydrogen production, and the possible involvement of reactive oxygen species (ROS)

Combined Theoretical and Exprimental Chracterization of Semicondcutors for Photoelectrocatalytic Applications

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Electrolyte Engineering toward Efficient Hydrogen Production Electrocatalysis with Oxygen-Crossover Regulation under Densely Buffered Near-Neutral pH Conditions

This study tackles the core issues associated with near-neutral pH water splitting, particularly regarding electrolyte engineering in the electrocatalysis and product crossover. The hydrogen evolution reaction (HER) was investigated on Pt, Ni, and NiMo catalysts in various concentrations of cations and anions to describe their performances by quantifying kinetics and mass transport. The choice of electrolyte in terms of its identity and activity drastically altered the HER performance. Electrolyte properties (activity coefficient, kinematic viscosity, and diffusion coefficient) accurately described the mass-transport contribution, which was easily isolated when a highly active Pt catalyst was used. The HER rate on the Pt was maximized by tuning the solute concentration (typically 1.5 to 2.0 M). Moreover, the kinematic viscosity and oxygen solubility under such densely buffered conditions governed the oxygen mass-transport flux in the electrolyte, which, in turn, tuned the crossover flux. At near-neutral pH, as high as 90% selectivity toward the HER was achieved even under an oxygen-saturated condition, where only a 40 mV overpotential was needed to achieve 10 mA cm^–2 for the HER. This information can be regarded as an important milestone for achieving a highly efficient water splitting system at near-neutral pH

Electrocatalytic Hydrogen Evolution under Densely Buffered Neutral pH Conditions

Under buffered neutral pH conditions, solute concentrations drastically influence the hydrogen evolution reaction (HER). The <i>iR</i>-free HER performance as a function of solute concentration was found to exhibit a volcano-shaped trend in sodium phosphate solution at pH 5, with the maximum occurring at 2 M. A detailed microkinetic model that includes calculated activity coefficients, solution resistance, and mass-transport parameters accurately describes the measured values, clarifying that the overall HER performance is predominantly governed by mass-transport of slow phosphate ions (weak acid). In the HER at the optimum concentration of approximately 2 M sodium phosphate at pH 5, our theoretical model predicts that the concentration overpotential accounts for more than half of the required overpotential. The substantial concentration overpotential would originate from the electrolyte property, suggesting that the proper electrolyte engineering will result in an improved apparent HER performances. The significance of concentration overpotential shown in the study is critical in the advancement of electrocatalysis, biocatalysis, and photocatalysis

New Insight into the Hydrogen Evolution Reaction under Buffered Near-Neutral pH Conditions: Enthalpy and Entropy of Activation

Electrochemical conversion of thermodynamically stable chemicals of water and carbon dioxide is regarded as a core technology for achieving sustainability in our society. In both cases, the electrochemical hydrogen evolution reaction (HER) is a key reaction, particularly at near-neutral pH. This study addresses the kinetic aspects of the HER in buffered near-neutral pH conditions using a variety of electrode materials (W, Ni, Pt, Au, and Cu) over a wide temperature range (299–346 K). When the overall performance was summarized with respect to the binding energy of the reaction intermediate species, a classic volcano-shaped relationship was obtained. Interestingly, the temperature sensitivity analysis disclosed that smaller activation energies did not always lead to higher performance in 1.5 mol L^–1 K-phosphate solution (pH 5.8). Detailed analysis of the temperature- and potential-dependent parameters revealed that smaller activation energies coincided with smaller values of the pre-exponential factor in the Arrhenius’ equation (associated with the entropy of activation). Due to the trade-off relationship of enthalpy–entropy compensation in the current system, the conventional approach of mixing elements of lower and higher binding energies to the intermediate species failed: even though Ni–Cu showed lower apparent activation energy, its activity toward the HER was between that of Ni and Cu due to the lowered entropy of activation. This study demonstrates the unrevealed fundamental aspects of the HER in buffered near-neutral condition, which contributes to the rational development of efficient energy and material conversion systems