Search Results (5)

Normal root growth is essential for the plant uptake of soil nutrients and water. However, exogenous H₂O₂ inhibits the gravitropic growth of pea primary roots. It has been shown that CaCl₂ application can alleviate H₂O₂ inhibition, but the exact alleviation mechanism is not clear. Therefore, the present study was carried out by combining the transcriptome and metabolome with a view to investigate in depth the mechanism of action of exogenous CaCl₂ to alleviate the inhibition of pea primordial root gravitropism by H₂O₂. The results showed that the addition of CaCl₂ (10 mmol·L⁻¹) under H₂O₂ stress (150 mmol·L⁻¹) significantly increased the H₂O₂ and starch content, decreased peroxidase (POD) activity, and reduced the accumulation of sugar metabolites and lignin in pea primary roots. Down-regulated genes regulating peroxidase, respiratory burst oxidase, and lignin synthesis up-regulated PGM1, a key gene for starch synthesis, and activated the calcium and phytohormone signaling pathways. In summary, 10 mmol·L⁻¹ CaCl₂ could alleviate H₂O₂ stress by modulating the oxidative stress response, signal transduction, and starch and lignin accumulation within pea primary roots, thereby promoting root gravitropism. This provides new insights into the mechanism by which CaCl₂ promotes the gravitropism of pea primary roots under H₂O₂ treatment. Full article

The activity of emission control catalysts must be improved in urban mode at low temperatures. One possible way is to tailor the metal-support interaction between platinum group metals (PGMs) and ceria to stabilize small clusters or single atoms, optimizing the utilization of costly PGMs. In this study, a small loading of Pd (<0.2 wt.%) was dispersed on Pr-rich cerium–zirconium–praseodymium mixed oxides (CZP45: Ce_0.45Zr_0.10Pr_0.45O_2−x). After the initial calcination at 800 °C, Pd was mainly in the form of dispersed isolated cations which were found to be efficient for low-temperature CO oxidation but inactive for propane combustion. Nevertheless, a pre-reduction step can trigger the formation of Pd nanoparticles and promote the propane oxidation. Pd nanoparticles, formed during the reduction step, coupled with the high oxygen mobility of CZP45, lead to outstanding catalytic activity for propane oxidation starting from 250 °C. However, the re-oxidation of Pd nanoparticles and their partial re-dispersion, promoted by the fast oxygen mobility of the mixed oxide, rapidly deactivate the catalysts in lean conditions. Full article

Scientific and technological innovation is increasingly playing a role for promoting the transition towards a circular economy and sustainable development. Thanks to its dual function of harvesting energy from waste and cleaning up waste from organic pollutants, microbial fuel cells (MFCs) provide a revolutionary answer to the global environmental challenges. Yet, one key factor that limits the implementation of larger scale MFCs is the high cost and low durability of current electrode materials, owing to the use of platinum at the cathode side. To address this issue, the scientific community has devoted its research efforts for identifying innovative and low cost materials and components to assemble lab-scale MFC prototypes, fed with wastewaters of different nature. This review work summarizes the state-of the-art of developing platinum group metal-free (PGM-free) catalysts for applications at the cathode side of MFCs. We address how different catalyst families boost oxygen reduction reaction (ORR) in neutral pH, as result of an interplay between surface chemistry and morphology on the efficiency of ORR active sites. We particularly review the properties, performance, and applicability of metal-free carbon-based materials, molecular catalysts based on metal macrocycles supported on carbon nanostructures, M-N-C catalysts activated via pyrolysis, metal oxide-based catalysts, and enzyme catalysts. We finally discuss recent progress on MFC cathode design, providing a guidance for improving cathode activity and stability under MFC operating conditions. Full article

Recent studies have shown that the catalytic performance (activity and/or selectivity) of Pt-group metal (PGM) catalysts for the CO and hydrocarbons oxidation as well as for the (CO, HCs or H₂)-SCR of NO_x or N₂O can be remarkably affected through surface-induced promotion by successful application of electropositive promoters, such as alkalis or alkaline earths. Two promotion methodologies were implemented for these studies: the Electrochemical Promotion of Catalysis (EPOC) and the Conventional Catalysts Promotion (CCP). Both methodologies were in general found to achieve similar results. Turnover rate enhancements by up to two orders of magnitude were typically achievable for the reduction of NO_x by hydrocarbons or CO, in the presence or absence of oxygen. Subsequent improvements (ca. 30–60 additional percentage units) in selectivity towards N₂ were also observed. Electropositively promoted PGMs were also found to be significantly more active for CO and hydrocarbons oxidations, either when these reactions occur simultaneously with deNO_x reactions or not. The aforementioned direct (via surface) promotion was also found to act synergistically with support-mediated promotion (structural promotion); the latter is typically implemented in TWCs through the complex (Ce–La–Zr)-modified γ-Al₂O₃ washcoats used. These attractive findings prompt to the development of novel catalyst formulations for a more efficient and cost-effective control of the emissions of automotives and stationary combustion processes. In this report the literature findings in the relevant area are summarized, classified and discussed. The mechanism and the mode of action of the electropositive promoters are consistently interpreted with all the observed promoting phenomena, by means of indirect (kinetics) and direct (spectroscopic) evidences. Full article

Direct decomposition of NO into N₂ and O₂ (2NO→N₂ + O₂) is recognized as the “ideal” reaction for NOx removal because it needs no reductant. It was reported that the spinel Co₃O₄ is one of the most active single-element oxide catalysts for NO decomposition at higher reaction temperatures, however, activity remains low below 650 °C. The present study aims to investigate new promoters for Co₃O₄, specifically PdO vs. PtO. Interestingly, the PdO promoter effect on Co₃O₄ was much greater than the PtO effect, yielding a 4 times higher activity for direct NO decomposition at 650 °C. Also, Co₃O₄ catalysts with the PdO promoter exhibit higher selectivity to N₂ compared to PtO/Co₃O₄ catalysts. Several characterization measurements, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H₂-temperature programmed reduction (H₂-TPR), and in situ FT-IR, were performed to understand the effect of PdO vs. PtO on the properties of Co₃O₄. Structural and surface analysis measurements show that impregnation of PdO on Co₃O₄ leads to a greater ease of reduction of the catalysts and an increased thermal stability of surface adsorbed NOx species, which contribute to promotion of direct NO decomposition activity. In contrast, rather than remaining solely as a surface species, PtO enters the Co₃O₄ structure, and it promotes neither redox properties nor NO adsorption properties of Co₃O₄, resulting in a diminished promotional effect compared to PdO. Full article