The Competition between 4-Nitrophenol Reduction and BH₄⁻ Hydrolysis on Metal Nanoparticle Catalysts

Assessing competitive environmental catalytic reduction processes via NaBH4 is essential, as BH4− is both an energy carrier (as H2) and a reducing agent. A comprehensive catalytic study of the competition between the borohydride hydrolysis reaction (BHR, releasing H2) and 4-nitrophenol reduction via BH4− on M0- and M/M′ (alloy)-nanoparticle catalysts is reported. The results reveal an inverse correlation between the catalytic efficiency for BH4− hydrolysis and 4-nitrophenol reduction, indicating that catalysts performing well in one process exhibit lower activity in the other. Plausible catalytic mechanisms are discussed, focusing on the impact of reaction products such as 4-aminophenol and borate on the rate and yield of BH4− hydrolysis. The investigated catalysts were Ag0, Au0, Pt0, and Ag/Pt-alloy nanoparticles synthesized without any added stabilizer. Notably, the observed rate constants for the 4-nitrophenol reduction on Ag0, Ag-Pt (9:1), and Au0 are significantly higher than the corresponding rate constants for BH4− hydrolysis, suggesting that most reductions do not proceed through surface-adsorbed hydrogen atoms, as observed for Pt0 nanoparticles. This research emphasizes the conflicting nature of BH4− hydrolysis and reduction processes, provides insights for designing improved catalysts for competitive reactions, and sheds light on the catalyst properties required for each specific process

Water Oxidation Catalyzed by Cobalt(II) Adsorbed on Silica Nanoparticles

A novel, highly efficient, and stable water oxidation catalyst was prepared by a pH-controlled adsorption of Co­(II) on ∼10 nm diameter silica nanoparticles. A <i>lower limit</i> of ∼300 s^–1 per cobalt atom for the catalyst turnover frequency in oxygen evolution was estimated, which attests to a very high catalytic activity. Electron microscopy revealed that cobalt is adsorbed on the SiO₂ nanoparticle surfaces as small (1–2 nm) clusters of Co­(OH)₂. This catalyst is optically transparent over the entire UV–vis range and is thus suitable for mechanistic investigations by time-resolved spectroscopic techniques

Synthesis of a SiO₂/Co(OH)₂ Nanocomposite Catalyst for SO_X/NO_X Oxidation in Flue Gas

Sulfur and nitrogen oxides (SOX/NOX) are the primary air toxic gas pollutants emitted during fuel combustion, causing health and environmental concerns. Therefore, their emission in flue gases is strictly regulated. The existing technologies used to decrease SOX/NOX content are flue gas desulfurization, which necessitates high capital and operating costs, and selective catalytic reduction, which, in addition to these costs, requires expensive catalysts and high operating temperatures (350–400 °C). New wet scrubbing processes use O3 or H2O2 oxidants to produce (NH4)2SO4 and NH4NO3 fertilizers upon ammonia injection. However, these oxidants are expensive, corrosive, and hazardous. SiO2/Co(OH)2 nanocomposites are presented here as potential catalysts for SOX/NOX oxidation in wet scrubber reactors to scrub these toxic gases using atmospheric oxygen as the oxidant at relatively low temperatures of 60–90 °C. Several silica-cobalt-oxide-based nanocomposites were synthesized as potential catalysts at different concentrations and temperatures. The nanocomposite catalysts were characterized and exhibited excellent catalytic properties for SOX/NOX oxidation using atmospheric oxygen as the oxidant, replacing the problematic H2O2/O3. We thus propose SiO2-supported Co(OH)2 nanoparticles (NPs) as excellent catalysts for the simultaneous scrubbing of polluting SOX/NOX gases in flue gases using atmospheric O2 as the oxidation reagent at a relatively low-temperature range

Manganese Carbonate (Mn₂(CO₃)₃) as an Efficient, Stable Heterogeneous Electrocatalyst for the Oxygen Evolution Reaction

With the growing population and energy demand, there is an urgent need for the production and storage of clean energy obtained from renewable resources. Water splitting electrocatalytically is a major approach to obtain clean H2. The efficiency, stability, and slow kinetics of anode materials developed so far do not fit the commercial application of the water oxidation reaction. To develop an efficient energy conversion catalyst, particularly for the oxygen evolution reaction (OER) herewith, Mn2(CO3)3 was electrodeposited on a Ni foam (NF) electrode surface by the chronoamperometric technique. The deposited Mn2(CO3)3/NF was characterized using various surface characterization techniques. The electrochemical behavior of the Mn2(CO3)3/NF-deposited electrode toward the OER was studied using electrochemical methods in KOH (pH 14) and NaHCO3 (pH 8.3) electrolytes. The Mn2(CO3)3/NF electrode showed a lower overpotential than CO3/NF and NF electrodes in the KOH/NaHCO3 media. The Mn2(CO3)3/NF electrode performs high electrocatalytic water oxidation with an overpotential of 360 mV at a current density of 10 mA·cm–2. This overpotential is much lower than those of CO3/NF (460 mV) and bare NF (520 mV), with good long-term stability in the KOH medium without any catalytic degradation after 100 CV cycles and 15 h chronoamperometric studies. The stability of the electrodeposited Mn2(CO3)3 on the NF electrode was determined by X-ray photoelectron spectroscopy. Thus, the Mn2(CO3)3/NF catalyst is suitable for the oxygen evolution reaction

Nano-encapsulation: overcoming conductivity limitations by growing MOF nanoparticles in meso-porous carbon enables high electrocatalytic performance

MOFs uniquely combine metal-atom centers and developed organic-based structures. Both features are attractive for catalysis. However, their isolating nature prevents them from effective use in electrocatalysis processes. Modifying the chemical structure to gain electric conductivity often harms its natural advantages. In this study, Borenstein et al. present a new approach to overcoming the non-conductivity of MOF b growing MOF nanoparticles in a conductive carbon host. The host’s porosity controls the MOF nanoparticles’ size and their electric properties while preserving their structure. As a result, the composition efficiently electro-catalyzes carbon dioxide into formic acid at low overpotentials