Highly Stable Perovskite Oxides for Electrocatalytic Acidic NOx - Reduction Streamlining Ammonia Synthesis from Air.

Electrochemical nitrogen oxide ions reduction reaction (NOx -RR) shows great opportunity for ammonia production under ambient conditions. Yet, performing NOx -RR in strong acidic conditions remains challenging due to the corrosion effect on the catalyst and competing hydrogen evolution reactions. Here, we demonstrate a stable La1.5Sr0.5Ni0.5Fe0.5O4 perovskite oxide for the NOx -RR at pH 0, achieving a Faradaic efficiency for ammonia of approaching 100 % at a current density of 2 A cm-2 in a H-type cell. At industrially relevant current density, the NOx -RR system shows stable cell voltage and Faradaic efficiency for >350 h in membrane electrode assembly (MEA) at pH 0. By integrating the catalyst in a stacked MEA with a series connection, we have successfully obtained a record-breaking 2.578 g h-1 NH3 production rate at 20 A. This catalyst's unique acid-operability streamlines downstream ammonia utilization for direct ammonium salt production and upstream integration with NOx sources. Techno-economic and lifecycle assessments reveal substantial economic advantages for this ammonia production strategy, even when coupled with a plasma-based NOx production system, presenting a sustainable complement to the conventional Haber-Bosch process.

Ibuprofen Adsorption on Activated Carbon: Thermodynamic and Kinetic Investigation via the Adsorption Dynamic Intraparticle Model (ADIM).

The adsorption efficiency of commercial activated carbon toward ibuprofen (IBU) was investigated and described using the adsorption dynamic intraparticle model (ADIM). Although the adsorption capacity of activated carbon has been widely studied, the kinetic models used in the literature are simplified, treating adsorption kinetics with pseudo-kinetic approaches. In this paper, a realistic model is proposed, quantitatively describing the influence of the main operation parameters on the adsorption kinetics and thermodynamics. The thermodynamic data were interpreted successfully with the Freundlich isotherm, deriving an endothermic adsorption mechanism. The system was found to be dominated by the intraparticle diffusion regime, and the collected data allowed the determination of the surface activation energy (ES = 60 ± 7 kJ/mol) and the fluid-solid apparent activation energy (EA = 6 ± 1 kJ/mol). The obtained parameters will be used to design adsorption columns, allowing the scale-up of the process.

Diffusion measurements of hydrocarbons in H-MCM-41 extrudates with pulsed-field gradient nuclear magnetic resonance spectroscopy.

Mesoporous materials are promising catalysts for production of biofuels. Herein, H-MCM-41 catalysts with different concentrations of the silica Bindzil binder (10-50 wt%) were prepared and characterized using pulsed-field gradient (PFG) NMR in the powder form and as extrudates. Effective diffusion coefficients (De) are measured in all cases. Diffusivities of n-hexadecane were found smaller for extrudates as compared to the powder catalysts. The estimates of diffusive tortuosity were also determined. PFG NMR data showed one major component that reveals diffusion in interconnected meso- and micropores and one other minor component (1-2%) that may correspond to more isolated pores or may represent complex effects of restricted diffusion. Therefore, several approaches including initial slope analysis of spin-echo attenuation curves, two-component fitting and Laplace inversion were used to discuss different aspects of diffusional transport in the studied H-MCM-41 materials. Correlations between De and the amount of Bindzil, the specific surface area, the micropore volume, the particle size, the total acid sites and the Lewis acid sites are discussed.

Zeta Potential of Beta Zeolites: Influence of Structure, Acidity, pH, Temperature and Concentration.

Measurements of the zeta potential of solid heterogeneous supports are important for preparation of metal supported catalysts and for shaping zeolites into extrudates. In the current work, different types of heterogeneous support materials such as SiO2, Al2O3, and a range of beta zeolites of different silica- to-alumina ratio were analysed. It was observed that parameters such as temperature, pH and acidity significantly affect the zeta potential. In several instances, depending on the materials' acidity and microstructure, maxima in zeta potential were observed. The solid materials were thoroughly characterized using XRD, SEM, EDX, TEM, nitrogen physisorption, Al-NMR and FTIR with pyridine before zeta potential measurements.

Direct Reductive Amination of HMF to 5-(Aminomethyl)-2-furanmethanol Using Supported Iridium-based Catalysts.

In this work, partial reductive amination of 5-hydroxymethylfurfural (HMF) with gaseous ammonia over iridium supported on γ-Al2O3, TiO2, SiO2 and carbon has been studied. The influence of the support and pressure was investigated in the valorization under mild conditions of HMF to 5-(aminomethyl)-2-furanmethanol (AMFM). The catalysts were characterized by TEM, SEM-EDS, N2 sorption Isotherms, TGA, CO-Chemisorption, TPR, XRD, NH3-TPD, ICP-AES and XPS. The maximum activity and high rates were obtained for all catalytic systems. At 50 minutes of the reaction the Ir/C catalyst achieved 93 % of conversion and exhibited the highest yield and selectivity of 92 % and 99 % respectively, to the desired product 5-(aminomethyl)-2-furanmethanol. The main properties that influence activity and selectivity are related to the amount of iridium on the surface and catalyst acidity. After the third cycle, 63 % and 59 % of selectivity and yield to AMFM respectively at 93 % of conversion were obtained.

Dendritic ZSM-5 zeolites as highly active catalysts for the valorization of monoterpene epoxides.

Dendritic ZSM-5 zeolites were investigated in the isomerization of monoterpene epoxides, including limonene-1,2-epoxide (LE), α-pinene epoxide, and ß-pinene epoxide, which yields high-value compounds used in fragrances, cosmetics, and pharmaceuticals. The fresh catalysts were thoroughly characterized using XRD, Ar physisorption, pyridine-FTIR, TEM, FTIR/DTBPyr, and 27Al MAS NMR. In comparison with conventional and hierarchical ZSM-5 materials, the dendritic zeolite with a crystallization time of 4 days (d-ZSM-5/4d) was the most active material, with a turnover frequency value of 4.4 min-1 for LE isomerization. Likewise, remarkable yields of dihydrocarvone (DHC, 63%, 70 °C, 2 h), campholenic aldehyde (72.4%, 70 °C, 5 min), and myrtanal (47.7%, 50 °C, 5 min) were obtained with this material that exhibited the largest mesopore/external surface area (360 m2 g-1), showing also the narrowest mesopore size distribution. A direct relationship was observed between the TOF values and the concentration of external Brønsted acid sites, showing the presence of strong steric/diffusional limitations that are greatly overcome with the dendritic zeolites. The lower reactivity of trans-LE compared to cis-LE was attributed to the larger steric hindrance of the oxygen atom. Exploration of the solvent influence revealed that the reaction rate of LE was favored by non-polar solvents, while highly selective DHC formation occurred in the solvents of medium polarity. The d-ZSM-5/4d sample was shown to be robust because catalytic activity could be completely recovered by air calcination.

Preparation, acid modification and catalytic activity of kaolinite nanotubes in α-pinene oxide isomerization.

In this work kaolinite nanotubes (KNT) were obtained from commercial kaolin AKF-78 (Uzbekistan) by starting material sequential intercalation by DMSO and methanol, followed by treatment with a cetyltrimethylammonium chloride solution. Acid functionalization of KNT for catalytic applications was successfully performed for the first time using a two-step treatment with piranha solution (H2SO4-H2O2), which resulted in the removal of organic impurities as synthetic artifacts and an increase in specific surface area by 3.9 times (up to 159 m2 g-1), pore volume by 1.5 times (0.23 cm3 g-1) and acidity by 4.1 times (49 µmol g-1). The values of the porous structure parameters and concentration of acid sites in processed kaolinite nanotubes practically corresponded to those for natural halloysite nanotubes (HNT) modified in the same way. Both types of materials demonstrated catalytic activity in the model reaction of α-pinene oxide isomerization in various solvents, including green ones, with selectivity to trans-carveol up to 55-57% and campholenic aldehyde of 50-51%, depending on the medium used. A satisfactory correlation between solvent polarity and selectivity was also observed. To the best of our knowledge, this is the first example of using modified kaolinite nanotubes per se as a catalyst. Overall, treatment of KNT with piranha solution provides not only catalytic activity but also the opportunity for further functionalization and application of these nanomaterials.

Oxygen-assisted hydroxymatairesinol dehydrogenation: a selective secondary-alcohol oxidation over a gold catalyst.

Selective dehydrogenation of the biomass-derived lignan hydroxymatairesinol (HMR) to oxomatairesinol (oxoMAT) was studied over an Au/Al(2)O(3) catalyst. The reaction was carried out in a semi-batch glass reactor at 343 K under two different gas atmospheres, namely produced through synthetic air or nitrogen. The studied reaction is, in fact, an example of secondary-alcohol oxidation over an Au catalyst. Thus, the investigated reaction mechanism of HMR oxidative dehydrogenation is useful for the fundamental understanding of other secondary-alcohol dehydrogenation over Au surfaces. To investigate the elementary catalytic steps ruling both oxygen-free- and oxygen-assisted dehydrogenation of HMR to oxoMAT, the reactions were mimicked in a vacuum over an Au(28) cluster. Adsorption of the involved molecular species--O(2), three different HMR diastereomers (namely, one SRR and two RRR forms), and the oxoMAT derivative--were also studied at the DFT level. In particular, the energetic and structural differences between SRR-HMR and RRR-HMR diastereomers on the Au(28) cluster were analyzed, following different reaction pathways for the HMR dehydrogenation that occur in presence or absence of oxygen. The corresponding mechanisms explain the higher rates of the experimentally observed oxygen-assisted reaction, mostly depending on the involved HMR diastereomer surface conformations. The role of the support was also elucidated, considering a very simple Au(28) charged model that explains the experimentally observed high reactivity of the Au/Al(2)O(3) catalyst.

Effect of CNT over structural properties of SAPO-34 in MTO process: Experimental and molecular simulation studies.

The hierarchical silicoaluminophosphate (SAPO-34) catalyst was synthesized using the mixtures of diethylamine (D) and butylamine (B) as a structure-directing agent (SDA), and carbon nanotube (CNT) as a secondary template in the hydrothermal method. The catalysts were characterized by Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), N2 physisorption, and temperature-programmed desorption of ammonia (NH3-TPD) techniques and evaluated for the catalytic activity in the Methanol to Olefins (MTO) process. The results showed that the use of CNT as the secondary template improved the hierarchical structure of SAPO-34 due to increasing the external surface area and mesoporosity and decreasing the particle size and as a result, made better the performance of the prepared SAPO-34 zeolite in the MTO process. Among all the prepared samples, the CNT-B-D catalyst synthesized by mixing three templates displayed the highest ethylene and propylene selectivity of 49% and 34%, respectively. Also, using CNT in the synthesis of samples increased the catalytic stability. In addition, pure, binary, and ternary adsorption isotherms and diffusivities of the main products and reactants over the SAPO-34 were investigated by theoretical measurements, because sorption and diffusion affect the catalyst stability and C2-C3 selectivity in the MTO reaction. The higher diffusion rate of ethylene leads to following the aromatic-based cycle in the MTO process.

Carboxymethylation of Cinnamyl Alcohol with Dimethyl Carbonate over Graphitic Carbon Nitrides.

A set of graphitic carbon nitride samples was prepared using a straightforward experimental procedure without templates and any subsequent treatments. The materials were studied in-depth using a range of physical and chemical methods such as X-ray diffraction, FTIR spectroscopy, elemental analysis (CHN), nitrogen physisorption, SEM, XPS, TPD CO2 . The resulting g-C3 N4 was shown to be highly efficient in carboxymethylation of cinnamyl alcohol with dimethyl carbonate yielding up to ca. 82 % of the desired cinnamyl methyl carbonate. In the studied conditions, an increase in the surface N atomic content leads to an increase in selectivity towards the desired carbonate, while a higher surface O content was beneficial for side products. Metal-free graphitic carbon nitride was shown to be one of the most productive (ca. 2 mol/h kgcat ) in the investigated reaction among studied heterogeneous catalysts.