Catalytic Tests Research Articles

Active Probing of a RuO2/CZ Catalyst Surface as a Tool for Bridging the Gap Between CO Oxidation Catalytic Tests in a Model and Realistic Exhaust Gas Stream

Active Probing of a RuO₂/CZ Catalyst Surface as a Tool for Bridging the Gap Between CO Oxidation Catalytic Tests in a Model and Realistic Exhaust Gas Stream

Hierarchically structured nanospherical fibrous silica-supported bimetallic catalysts: An enhanced performance in methane decomposition

Hydrogen production by methane catalytic decomposition is a promising method that also allows the formation of valuable carbon nanomaterials which can be utilized in transportation fuels, chemical synthesis, and fuel cell technology. In this study, bimetallic 3d transition metal (Ni, Fe, Co) catalysts supported on spherical mesoporous nanofibrous silica (KCC1) were successfully synthesized using a hydrothermal method followed by sono co-impregnation. The catalysts were evaluated for their performance in the catalytic decomposition of methane. Comprehensive characterization of the catalysts was conducted utilizing XRD, FTIR, SEM, TEM, STEM, XPS, H2-TPR, and BET techniques. XRD and TEM analyses confirmed the formation of Ni–Fe, Ni–Co, and Co–Fe bimetallic alloys on the nanofibrous silica without compromising its dendrimeric hierarchical structure. STEM HAADF imaging revealed a uniform dispersion of bimetallic nanoparticles within the spherical fibrous framework. Catalytic tests demonstrated that all bimetallic catalysts showed high stability and activity for methane cracking at 700 °C over 180 min of time on stream (TOS). Among them, Fe-based catalysts Ni–Fe/KCC1 and Co–Fe/KCC1 achieved the highest hydrogen yields of 80% and 60%, respectively. Methane conversion was 1.56 and 2.23 times higher in Ni–Fe/KCC1 compared to Co–Fe/KCC1 and Ni–Co/KCC1, respectively. Post-reaction characterization of the spent catalysts was performed using XRD, Raman spectroscopy, SEM, TEM, and TGA. XRD and Raman spectroscopy were used to evaluate the degree of graphitization and crystallinity in the carbon nanotubes (CNTs) produced on the catalysts, enabling a correlation with the catalyst properties. TEM examination was used to investigate the structural morphology and growth methods of the CNTs, including tip or base growth and chain-like or parallel-wall types. TGA results revealed that all bimetallic catalysts exhibited no amorphous carbon during methane cracking reaction.

SBA-15 supported Ni-Cu catalysts for hydrodeoxygenation of m-cresol to toluene.

Amidst concerns over fossil fuel dependency and environmental sustainability, the utilization of biomass-derived aromatic compounds emerges as a viable solution across diverse industries. In this scheme, the conversion of biomass involves pyrolysis, followed by a hydrodeoxygenation (HDO) step to reduce the oxygen content of pyrolysis oils and stabilize the end products including aromatics. In this study, we explored the properties of size controlled NiCu bimetallic catalysts supported on ordered mesoporous silica (SBA-15) for the catalytic gas-phase HDO of m-cresol, a lignin model compound. We compared their performances with monometallic Ni and Cu catalysts. The prepared catalysts contained varying Ni to Cu ratios and featured an average particle size of approximately 2 nm. The catalytic tests revealed that the introduction of Cu alongside Ni enhanced the selectivity for the direct deoxygenation (DDO) pathway, yielding toluene as the primary product. Optimal performance was observed with a catalyst composition comprising 5wt.% Ni and 5wr.% Cu, achieving 85% selectivity to toluene. Further increasing the Cu content improved turnover frequency (TOF) values, but reduced DDO selectivity. These findings underscore the importance of catalyst design in facilitating biomass-derived compound transformations and offer insights into optimizing catalyst composition for more selective HDO reactions.

Synthesis Route to Single-Walled Zeolite Nanotubes Enabled by Tetrabutylammonium Hydroxide.

Single-walled zeolite nanotubes (ZNT) were recently synthesized in a narrow compositional window. ZNT structural features-thin zeolitic walls and large mesopores-can allow for easy access of small molecules to zeolite micropores, but they also impart processing limitations for these materials, such as challenges with conventional aqueous ion-exchange conditions. Conventional solid- and liquid-phase ion exchange of calcined NaOH-derived ZNT (NaH-ZNT) results in structural degradation to either 2D sheet-like phases, 3D nanocrystals, or amorphous phases, motivating different direct synthesis routes and unconventional ion-exchange procedures of uncalcined ZNT precursors. Here, a modified synthesis route for ZNT synthesis is introduced that facilitates facile ion exchange as well as incorporation of additional non-Al heteroatoms in the zeolite framework. Tetrabutylammonium hydroxide (TBAOH) is used as a hydroxide source and co-OSDA, enabling synthesis of new compositions of ZNT, otherwise unachievable by post-modification of previously reported NaH-ZNT. By varying the gel composition, synthesis temperature, crystallization time, hydroxide source, silicon source, and aluminum source, productive conditions for the new TBAOH synthesis are developed, leading to increased strong acid site density in the ZNT. The collected results demonstrate the sensitivity of the ZNT synthesis to many key parameters and show that the ZNT forms only when Si/(Al + T) ∼ 30 in these synthesis gels and with specific Si and Al sources, and always in the presence of trace Na+. Catalytic testing, via the tandem CO2 hydrogenation to methanol and methanol to aromatics reaction, shows that ZNTs provide adequate catalytic activity (acidity), relative to their conventional 3D counterparts in converting methanol to aromatic compounds.

Effects of adding metals to Beta zeolite on ethanol conversion to hydrocarbons

This study investigated the effects of Beta zeolite ion exchange with Fe, Zn, and Co on ethanol conversion to hydrocarbons. Various characterization techniques such as X-ray fluorescence (XRF), inductively coupled plasma optical emission spectrometry (ICP-OES), X-ray diffraction (XRD), magic angle rotation nuclear magnetic resonance spectrometry (MAS NMR) of 29Si and 27Al, scanning electron microscopy (SEM), nitrogen physisorption, ammonia temperature-programmed desorption (NH3-TPD) and Fourier transform infrared spectroscopy (FTIR) were employed. Catalytic tests were performed at temperatures from 475 to 550 °C under ambient pressure. The metal addition to Beta zeolite reduced micropore area and volume, decreased the concentration of the extra-framework aluminum, and increased total acid site density and Lewis acid sites, except for Fe. For all catalysts, ethylene was identified as the primary product. However, catalysts containing Zn and Co displayed the formation of propylene and C1 to C3 paraffins. The catalyst with Fe exhibited the highest deactivation and a significant decrease in acidity, attributed to the formation of extra-framework aluminum, resulting in exclusive ethylene production.

N2O Decomposition on Singly and Doubly (K and Li)-Doped Co3O4 Nanocubes─Establishing Key Factors Governing Redox Behavior of Catalysts.

The intimate mechanism of N2O decomposition on bare and redox-tuned Co3O4 nanocubes (achieved by single (Li or K) and double (Li and K) doping) was elucidated. The catalysts synthesized by the hydrothermal method were characterized by X-ray electron absorption fine structure measurements, X-ray diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and Kelvin Probe techniques. TPSR and steady-state isothermal catalytic tests reveal that the N2O turnover frequencies are critically sensitive to the work function of the catalysts, adjusted purposely by doping. For the catalysts obtained by one-pot hydrothermal synthesis, lithiation of the Co3O4 nanocubes leads to the formation of {Li'8a, Co·16d} species, decreasing steadily the work function and the activity, while for the catalysts prepared by postsynthesis impregnation, formation of {Li'8a, Co'16d, Co··16c} species leads to a volcano-type dependence of the catalytic activity and the work function in parallel. The beneficial effect of potassium was discussed in terms of mitigation of surface potential buildup due to the accumulation of ionosorbed oxygen intermediates (surface electrostatics), which hinders the interfacial electron transfer. Analysis of the catalytic activity response to the redox tuning of Co3O4, substantiated by DFT calculations, allowed for a straightforward conceptualization of the redox nature of the N2O decomposition in terms of the lineup of frontier orbitals of the N2O/N2O- and O2-/O2 reactants with the surface DOS structure and the resultant molecular orbital interactions. The positions of the virtual bonding 3πg0(N2O)-α-3dz2 and the occupied 2πg1(O2-)-α-3dz2 states relative to the Fermi energy level play a crucial role in the regulation of the forward and backward interfacial electron transfer events, which drive the redox process.

Desulfurization reactions of thiophene and cyclohexane over Zn and Nb modified zeolites in FCC process

In refineries, one of the most important production units is Fluid Catalytic Cracking (FCC). In them, the incorporation of additives to the catalyst is a very interesting option to reduce the sulfur content of gasoline, and thus obtain commercial fuel specifications. In this study, the transformation of thiophene into a cyclohexane (HC) stream for its in-situ desulfurization has been investigated, using catalysts based on niobium or zinc (6 wt%) incorporated into three types of zeolites: HUSY, HBeta and HZSM-5. Catalytic tests were carried out at 773 K in an automatically controlled fixed-bed tubular reactor. The reaction products were analyzed online by gas chromatography, with FID detector for hydrocarbons and SCD for sulfur compounds, and the catalysts were characterized by XRD, FTIR, N2 adsorption isotherms, HRTEM, XRF, 29Si and 27Al solid state NMR, NH3-TPD and FTIR-pyridine techniques. The results indicate that the addition of metals did not significantly alter the textural and structural properties of the zeolites, and that the Nb/HB and Nb/HY catalysts were the most effective in the conversion of thiophene, and selective toward paraffins and H2S mainly. The performance of these materials was attributed to the existence of an optimal balance between the Brønsted and Lewis acid sites, which increased the hydrogen transfer coefficient (HTC) during the cyclohexane transformation, resulting in higher desulfurization activity. The addition of zinc drastically increased the density of the Lewis acid sites and decreased the HTC, favoring the production of aromatics and thiophene condensation reactions, thus transferring sulfur to the gasoline streams. In general, the catalysts investigated are of significant interest as additives for sulfur reduction in FCC gasoline streams, either by producing easily removable H2S or by transferring sulfur to heavier fractions.

Hydrogen Production from Methanol Steam Reforming over Fe-Modified Cu/CeO2 Catalysts.

Fe-modified Cu catalysts with CeO2 support, prepared by the impregnation method, were subjected to physicochemical analysis and catalytic tests in the steam reforming of methanol (SRM). Physicochemical studies of the catalysts were carried out using the XRF, TEM, STEM-EDS, XRD, TPR and nitrogen adsorption/desorption methods. XRD, TEM studies and catalytic tests of the catalysts were carried out at two reduction temperatures, 260 °C and 400 °C, to determine the relationship between the form and oxidation state of the active phase of the catalysts and the catalytic properties of these systems in the SRM. Additionally, the catalysts after the reaction were analysed for the changes in the structure and morphology using TEM methods. The presented results show that the composition of the catalysts, morphology, structure, form and oxidation state of the Cu and Fe active metals in the catalysts and the reaction temperature significantly impact their activity, selectivity and stability in the SRM process. The gradual deactivation of the studied catalysts under SRM conditions could result from the forming of carbon deposits and/or the gradual oxidation of the copper and iron phases under the reaction conditions.

Partial oxidation of cyclohexene over histidine-modified Cu-UiO-66 under aerobic conditions

Enzyme-inspired catalysis is an attractive approach for developing selective hydrocarbon partial oxidation processes. Here, histidine was introduced into defective UiO-66 metal–organic framework by ligand exchange, followed by Cu(II) ion insertion. Density functional theory modeling combined with X-ray Absorption spectroscopy revealed that Cu(II) has a higher affinity for open Zr-O node sites than for histidine, leading to a series of materials where Cu(II) ions are predominantly anchored to the Zr6O4(OH)4 nodes, while only minority fractions of Cu(II) are anchored to histidine. Catalytic testing for aerobic cyclohexene oxidation with tert-butyl hydroperoxide (t-BuOOH) in trifluorotoluene solution at 25 °C showed activity for cyclohexene oxidation to cyclohexenol and cyclohexenone, with high selectivity. Benchmark tests revealed that Cu and t-BuOOH are both essential for the reaction, yet t-BuOOH consumption was far inferior to product formation rates, suggesting a radical reaction pathway involving O2.

Highly Efficient Electrospun Silver Decorated Graphene Oxide Nanocomposites on Poly(vinylidene fluoride) (PVDF@GO-Ag) Hybrid Membrane for Reduction of 4-Nitrophenol.

Graphene oxide-silver poly(vinylidene fluoride) membranes (PVDF@GO-Ag) were successfully synthesized by the electrospinning method, which exhibited a high catalytic activity using the hydrogenation of 4-nitrophenol (4-NP) as a model reaction in a batch reaction study. The hybrid membranes doped with 1 wt% GO and 2 wt% Ag (PVDF-1-2) exhibited the most desired performance for the catalytic reduction of 4-NP. Importantly, PVDF-1-2 exhibited excellent cycling stability in 10 catalytic cycle tests and was highly amenable to separation. This property effectively addresses the significant challenges associated with the practical application of nanocatalysts. Furthermore, density-functional theory (DFT) calculations have demonstrated that the GO-Ag nanocomposites exhibit the strongest adsorption capacity for 4-NP- when a specific ratio of GO and Ag is achieved, accompanied by the loading of Ag nanoclusters onto GO. Additionally, the study demonstrated that an increase in temperature significantly accelerated the reaction rate, in line with the van't Hoff rule. This study provides an effective and environmentally friendly solution for the treatment of 4-NP in wastewater.

Elucidating the Synergistic Promotional Mechanism of Water and Oxygen in the Aerobic C-C Homocoupling Reaction Catalyzed by Visible-Light-Derived Core-Shell Pd@A-CQDs Nanostructures.

Rational design and precise synthesis of biogenic noble-metal-based catalysts possessing distinctive structure and composition play a crucial role in the chemical industry, enabling sustainable construction of an inclusive range of chemical resources. In this study, we have effectively fabricated Pd@A-CQDs through a straightforward one-pot aqueous protocol assisted by visible light employing renewable biomass-derived amine-rich carbon quantum dots (A-CQDs). The remarkable visible light harnessing capability (bandgap, ca. 2.81 eV), high density (35.7 × 1018 cm-3), and long lifetime (25 ps) of photocharge carriers and amine-rich surface in A-CQDs make them ideal candidates as both reducing and stabilizing agents, thereby facilitating the in situ construction of metallic Pd(0) nanoparticles. Comprehensive physicochemical characterizations have provided compelling evidence for the spherical morphology of Pd@A-CQDs core-shell nanostructures, with ultrathin A-CQDs shells of ca. 1.9 nm and an average diameter of 14 ± 1 nm. The effectiveness of the synthesized Pd@A-CQDs catalysts was assessed in the ligand- and base-free homocoupling reaction of arylboronic acids in water at ambient temperature. The catalytic tests demonstrated the selective production of the homocoupled compound over protodeboronation products with excellent yield and high catalyst recyclability under ambient conditions. The protocol employed exhibited a high TOF (1.05 × 10-2 mol g-1 min-1) and a low E-factor, with a remarkably low palladium loading. XPS analysis confirmed the retention of the metallic nature of the palladium core within the catalysts during the reaction. The catalytic function of the palladium core in conjunction with the A-CQDs shell, along with the promotional effects provided by water and oxygen for the formation of nucleophilic tetravalent boron, was conclusively recognized by 11B NMR and O2-TPD measurements. The obtained experimental results deliver valuable insights into the probable reaction pathway for the homocoupling reaction catalyzed by the Pd@A-CQDs catalysts. Through a comprehensive and sustainable evaluation, the current methodology exhibits superior performance compared to previously documented techniques in relation to estimated circularity and adherence to good manufacturing practices (GMP).

Selective catalytic reduction of NOx by NH3 at low temperature over Mn0.5Zr(0.5-x)Fex catalyst with different Fe/Zr ratios

ABSTRACT Through a basic co-precipitation technique, a series of Mn0.5Zr(0.5-x)Fex ternary oxide catalysts with different Fe/Zr ratios have been prepared and applied to the selective catalytic reduction of NOx. The results of catalytic activity test show that the Mn0.5Zr0.2Fe0.3 catalyst with a molar ratio of Fe/Zr of 3:2 has the most effective denitrification activity at low temperature and displays considerable tolerance to SO2 and H2O. The Mn0.5Zr0.2Fe0.3 catalyst exhibits a combination of physical and chemical attributes, including an elevated specific surface area and a homogeneously distributed active component, which collectively furnish additional points of interaction for the reacting gases, thus improving the catalytic performance. In addition, the high Mn4+/Mnn+ and Fe2+/Fen+ ratios, strong redox capacity, and more acidic sites on the surface of the catalyst also have positive effects on its denitrification performance. Meanwhile, the reaction process on Mn0.5Zr0.2Fe0.3 catalyst is driven by the Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms. This study provides an important reference for the design of Mn-based catalysts with high denitration performance and excellent resistance to SO2 and H2O.

Glycerol dry reforming over Ni supported on fibrous ZSM5 and ZY: Correlation of structural properties on H2 production

This study investigates fibrous ZSM5 (FZSM5) and Zeolite Y (FZY) as supports for producing hydrogen via glycerol dry reforming. The fibrous ZSM5 and ZY were synthesized hydrothermally with microemulsion and impregnated with 10 wt% Ni via a sonication method. The catalytic test was conducted via a vertical stainless steel fixed-bed rig, at 800°C with a glycerol/CO2 ratio of 1. XRD and N2 sorption revealed the reduced surface area and crystallinity in Ni/FZSM5 compared to Ni/FZY. Ni/FZY catalyst displayed a larger surface area (264 m2/g) and aperture width (6.70 nm) in comparison to Ni/FZSM5, which had a surface area of 238 m2/g and an aperture width of 3.90 nm. Ni/FZY also had a smaller NiO crystallite size (8.73 nm) than Ni/FZSM5 (9.79 nm), suggesting well-dispersed Ni species on the wrinkle fiber of FZY’s surface. Ni/FZY outperformed Ni/FZSM5 with 52.49 % glycerol conversion, 44.87 % H2 yield, 71.31 % CO yield, and only 14.4 % carbon formation, attributed to robust Ni-O-Si contact and larger pore diameter. The discovery highlights the catalytic efficiency of the Ni-loaded fibrous zeolite in GDR, offering versatility for application in energy storage and catalysis.

Reutilization of pyrite tailings in peracetic acid-based advanced oxidation process for water purification

Iron-based heterogeneous catalysts in peracetic acid (PAA)-based advanced oxidation technologies are currently a considerable interest, yet the sluggish reduction from Fe(III) to Fe(II) impedes the efficiency of PAA activation. Pyrite tailings (PRT) still contains a certain amount of FeS2 composition, and its reducing sulfur species have the ability of electron-donating for Fe(III) reduction. Therefore, from the view of resource utilization and environmental protection, we applied PRT to activate PAA for removing sulfamethoxazole (SMX) in this work. In-situ Raman spectra verified the activation of PAA by PRT, and 93.67 % of SMX (5 mg/L) can be removed after 50 min in near-neutral circumstance (pH 5.8), which could be mainly attributed to the activation of PAA through the leached Fe ions from PRT. Radical scavenging and probe tests testified that hydroxyl and acetylperoxy radicals are responsible for SMX decomposition. A series of spectroscopic characterizations and theory calculation confirmed that the ability of sulfur sites to donate electrons, thereby boosting Fe(II) regeneration on PRT. The continuous catalytic test proved the sustainable utilization capacity of PRT. This study presented PRT as an effective catalyst with potential uses for PAA-based wastewater treatment process.

Direct methane utilization through benzene dehydroalkylation catalyzed by Co2+ sites in ZSM-5 intersections

Cobalt cations exchanged in ZSM-5 are active for the direct dehydromethylation of benzene with CH4. While toluene is the primary product, an alternate reaction pathway leads also to the formation of biphenyl and phenyltoluene. This not only diminishes the selectivity but also contributes to the deactivation of the catalyst. Temperature-programmed surface reactions show that benzene adsorbs strongly on the exchanged Co2+ cations, essentially blocking the sites for alkylation below 400 °C. At temperatures exceeding 400 °C, the partial desorption of benzene enables its reaction with CH4, leading to the formation of toluene. The formation of biphenyl is kinetically hindered, and its onset is only observed at temperatures above 450 °C. When CH4 is allowed to chemisorb on Co2+ sites prior to exposure to benzene, the formation of toluene is detected at temperatures below 400 °C. By infrared spectroscopy of benzene adsorption and UV–Vis spectroscopic characterization, we identified the existence of intersections in ZSM-5 where three H+ are in proximity. The ion exchange of a zeolite lattice Al3+ pair in such positions leads to the formation of a Co2+ site near a free Brønsted acid site. We observed a correlation between the concentration of this type of Co2+ sites and the catalytic activity of Co-ZSM-5 in benzene alkylation with CH4. This is further supported by the catalytic tests of Co-ZSM-5 materials with specifically a larger proportion of Co sites in sinusoidal channels, as a result of acidic conditions during ion exchange. Based on this, we propose that toluene formation takes place via heterolytic dissociation of CH4 on a Co2+ site at intersections followed by reaction with benzene strongly interacting with an adjacent BAS.

Plasma-catalytic direct oxidation of methane to methanol over Cu-MOR: Revealing the zeolite-confined Cu2+ active sites

Efficient methane conversion to methanol remains a significant challenge in chemical industry. This study investigates the direct oxidation of methane to methanol under mild conditions, employing a synergy of non-thermal plasma and Cu-MOR (Copper-Mordenite) catalysts. Catalytic tests demonstrate that the Cu-MOR IE-3 catalyst (i.e., prepared by three cycles of ion exchange) exhibits superior catalytic performance (with 51 % methanol selectivity and 7.9 % methane conversion). Conversely, the Cu-MOR catalysts prepared via wetness impregnation tend to over-oxidize CH4 to CO and CO2. Through systematic catalyst characterizations (XRD, TPR, UV–Vis, HRTEM, XPS), we elucidate that ion exchange mainly leads to the formation of zeolite-confined Cu2+ species, while wetness impregnation predominantly results in CuO particles. Based on the catalytic performance, catalyst characterizations and in-situ FTIR spectra, we conclude that zeolite-confined Cu2+ species serve as the active sites for plasma-catalytic direct oxidation of methane to methanol.

Conversion of limonene to limonene diol over activated carbon supported Ti catalyst

AbstractA series of activated carbon supported Ti-3,3′-ethylen bis(3,4-dihydro-2H-1,3-benzoxazine) complex catalysts (denoted Ti-Bz (0.25)/AC, Ti-Bz(0.37)/AC, and Ti-Bz (0.5)/AC) was evaluated in the conversion of limonene to limonene diol using H2O2 as oxidant. The opening of oxazine ring as a step to the titanium complex formation was highlighted, as far as we are aware, for the first time, by NMR analysis. A range of characterization methods, including SEM–EDS, nitrogen physisorption, ATR-FTIR, and XRD, showed that the procedure used in the preparation of these materials was reproducible. Parameters affecting the catalytic performances in the production of limonene diol, such as reaction temperature, amount of catalyst tested, and its catalytic stability, were studied. Ti-Bz (0.5)/AC was the most performant catalyst leading to limonene diol yield of 36.7%. The recyclability of the catalyst was evaluated along three catalytic consecutive tests that showed no significant difference of performance compared with that of fresh catalyst.

CeCoaOx catalysts derived from metal-organic frameworks for enhancing catalytic toluene oxidation by tuning surface oxygen property

Rod-shaped CeCoaOx catalysts with varying Co doping ratios (a = 0.012, 0.017, 0.022) were synthesized by calcinating the Ce-MOF, prepared using a water bath and trimesic acid as an organic ligand. This method ensured a high degree of elemental mixing, abundant pore channels and a large specific surface area are all beneficial for enhancing toluene catalytic oxidation activity. Raman, XPS, and catalytic activity tests confirmed strong interactions between the Ce and Co oxides, promoting the formation of more Ce3+ and oxygen vacancies. Among these catalysts, CeCo0.012Ox exhibited superior catalytic performance for toluene oxidation under weight hourly space velocity of 40,000 mL·g−1·h−1. The temperature at toluene conversion of 10 %, 50 % and 90 % was 140, 205 and 226 °C, respectively, which was 61, 12 and 14 °C higher than those over pure phase CeO2. CeCo0.012Ox also demonstrated excellent activity stability under high humidity (10 vol%H2O). H2-TPR, O2-TPD and in situ DRIFTS also revealed that surface-absorbed oxygen species played a crucial role in catalytic activity, with CeCo0.012Ox benefiting from abundant oxygen vacancies and effective oxygen species mobility.

A Mechanistic Study on Iron-Based Styrene Aziridination: Understanding Epoxidation via Nitrene Hydrolysis.

Transition-metal-catalyzed nitrene transfer reactions are typically performed in organic solvents under inert and anhydrous conditions due to the involved air and water-sensitive nature of reactive intermediates. Overall, this study provides insights into the iron-based ([FeII(PBI)3](CF3SO3)2 (1), where PBI = 2-(2-pyridyl)benzimidazole), catalytic and stoichiometric aziridination of styrenes using PhINTs ([(N-tosylimino)iodo]benzene), highlighting the importance of reaction conditions including the effects of the solvent, co-ligands (para-substituted pyridines), and substrate substituents on the product yields, selectivity, and reaction kinetics. The aziridination reactions with 1/PhINTs showed higher conversion than epoxidation with 1/PhIO (iodosobenzene). However, the reaction with PhINTs was less selective and yielded more products, including styrene oxide, benzaldehyde, and 2-phenyl-1-tosylaziridine. Therefore, the main aim of this study was to investigate the potential role of water in the formation of oxygen-containing by-products during radical-type nitrene transfer catalysis. During the catalytic tests, a lower yield was obtained in a protic solvent (trifluoroethanol) than in acetonitrile. In the case of the catalytic oxidation of para-substituted styrenes containing electron-donating groups, higher yield, TON, and TOF were achieved than those with electron-withdrawing groups. Pseudo-first-order kinetics were observed for the stoichiometric oxidation, and the second-order rate constants (k2 = 7.16 × 10-3 M-1 s-1 in MeCN, 2.58 × 10-3 M-1 s-1 in CF3CH2OH) of the reaction were determined. The linear free energy relationships between the relative reaction rates (logkrel) and the total substituent effect (TE, 4R-PhCHCH2) parameters with slopes of 1.48 (MeCN) and 1.89 (CF3CH2OH) suggest that the stoichiometric aziridination of styrenes can be described through the formation of a radical intermediate in the rate-determining step. Styrene oxide formation during aqueous styrene aziridination most likely results from oxygen atom transfer via in situ iron oxo/oxyl radical complexes, which are formed through the hydrolysis of [FeIII(N•Ts)] under experimental conditions.

Assessment of sulfuric acid as pH control agent in catalytic nitrate reduction in drinking waters

H2SO4 was thoroughly assessed as an alternative to CO2 as pH controller, as it allows for to a much precise dosage control. Catalytic nitrate reduction tests using a Pd-Cu catalyst supported on a carbon black were performed using both Milli-Q grade and real natural drinking waters spiked with NO3– in batch reactors. Conversion and selectivity results were equivalent to those obtained for CO2 use, obtaining total NO3– conversion and final NH4+ selectivity around 30 % for a pH range of 5.5–6 using a 0.05 M H2SO4 solution. Good stability of the catalyst in natural drinking water with the higher salt content studied was observed through reaction cycles, despite the presence of SO42- in the reaction medium, with total NO3– conversion after four reaction cycles and final NH4+ concentration of less than 16 mg/L were obtained, making H2SO4 a promising alternative to CO2 as pH controller in the catalytic NO3– reduction.