Search Results (154)

The design of efficient catalysts is vital for the application of catalytic oxidation technology in the removal of gaseous pollutants. Herein, a series of MnO_x catalysts with the typical Mn₂O₃ crystal structure was synthesized via the high-temperature pyrolysis method by using Mn-based metal–organic frameworks (Mn-MOFs) with various morphologies as the precursors. The physicochemical properties of these Mn-MOF-derived MnO_x samples were investigated by various characterization techniques, including X-ray diffraction (XRD), thermogravimetry (TG), N₂ adsorption–desorption, scanning electron microscope (SEM), and H₂ temperature-programmed reduction (H₂-TPR), and their catalytic activity was evaluated for catalytic CO degradation. The results showed that the Mn-MOF with leaf-like morphology, derived MnO_x-Leaf, presented the optimal catalytic CO oxidation performance (T₉₈ = 214 °C), stability, and reusability. Characterization results showed that the different Mn-MOF-derived MnO_x catalysts possessed different physical–chemical properties. The superior catalytic activity of MnO_x-Leaf for CO degradation was ascribed to its large surface area and pore size, better low-temperature redox properties, and high H₂ consumption, which promoted the adsorption and activation of the CO and gaseous oxygen molecules, improving CO oxidation. Finally, the possible CO degradation pathway was evaluated by in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS), which showed that gaseous CO and O₂ were adsorbed on the surface of the catalyst and oxidized to form surface carbon-related species (bicarbonate and carbonate), and finally converted to CO₂. Full article

The Monastery of San Nicolò l’Arena in Catania, a UNESCO World Heritage site, embodies a complex architectural and historical stratigraphy, reflecting successive construction phases, functional changes, and the impact of catastrophic events, including the 1669 lava flow and the 1693 earthquake. As part of the CHANGES project, this study combines historical–archaeological research with non-invasive in situ scientific analyses to investigate the materials and the conservation state of the monumental complex. Stratigraphic analysis identified multiple masonry and plaster units, allowing the reconstruction of five main construction phases and related functional changes. Portable X-ray Fluorescence (pXRF), Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT), and handheld optical microscopy provided rapid insights into the chemical and mineralogical composition of plasters and mortars, highlighting lime-based binders with variable aggregate, including volcanic clasts, sand, and cocciopesto. In situ diagnostic analyses allowed us to distinguish pre- and post-earthquake materials, while historical data contextualized construction phases and functional transformations. The integration of archaeological and scientific approaches proved to be complementary: historical evidence guides the selection of analytical targets, while diagnostic results enrich and validate the interpretation of the building’s evolution. This interdisciplinary methodology establishes a robust framework for the understanding and valorization of complex cultural heritage sites. Full article

Propane is a typical volatile organic compound (VOC) in coal chemical processing and petroleum refining. However, coexisting SO₂ significantly impairs its catalytic oxidative removal, potentially causing catalyst poisoning and deactivation. This study systematically elucidated the inhibitory effects of SO₂ on the catalytic oxidation of propane over the Ru@CoMn₂O₄ catalyst system. Under continuous exposure to 30 ppm SO₂, propane conversion plummeted by 30% within two hours. Mechanistic studies revealed that SO₂ selectively bound to high-valent Mn sites rather than preferentially interacting with Co sites, leading to the formation of MnSO₄ particles. These particles were directly corroborated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. After four hours of exposure to SO₂, roughly 11.8 mole percent of manganese in the catalyst was converted into MnSO₄. These deposits physically blocked active sites, reduced specific surface area, and disrupted redox cycling. As a result, their combined effects diminished performance progressively, ultimately leading to complete deactivation. Furthermore, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) confirmed that SO₂ suppressed C=C bond oxidation in propane intermediates, thereby directly limiting conversion efficiency. Combining qualitative and quantitative methods, we characterized SO₂-induced poisoning during propane oxidation. This work provides guidelines and strategies for designing anti-sulfur catalysts at the elemental scale for the catalytic combustion of low-carbon alkanes. Full article

The photocatalytic reduction of CO₂ into valuable hydrocarbons presents significant potential. In this research, a ZnO/ZnAl₂O₄ composite photocatalyst was synthesized using the hydrothermal method, resulting in a marked enhancement in CO yield—approximately three times greater than that achieved with pure ZnAl₂O₄ nanoparticles. The formation of a Z-scheme heterojunction between ZnO and ZnAl₂O₄ was observed, characterized by low interfacial charge transfer resistance, an abundance of reaction sites, and optimized charge transport pathways. Within this composite, ZnO contributes additional vacancies, thereby increasing active sites and enhancing the separation and migration of photogenerated carriers. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis indicates that ZnAl₂O₄ facilitates the formation of key intermediates, such as *COOH and HCO₃⁻, thus promoting the conversion of CO₂ to CO. This study offers valuable insights into the design of heterogeneous catalysts with diverse active components to enhance the performance of CO₂ photocatalytic reduction through synergistic effects. Full article

Photothermal catalytic CO₂ conversion into chemicals that provide added value represents a promising strategy for sustainable energy utilization, yet the development of highly efficient, stable, and selective catalysts remains a significant challenge. Herein, we report a rationally designed p-n junction heterostructure, T-CZ-PBA (SC), synthesized via controlled pyrolysis of high crystalline Prussian blue analogues (PBA) precursor, which integrates CuCo alloy, ZnO, N-doped carbon (NC), and Zn^II-Co^IIIPBA into a synergistic architecture. This unique configuration offers dual functional advantages: (1) the abundant heterointerfaces provide highly active sites for enhanced CO₂ and H₂ adsorption/activation, and (2) the engineered energy band structure optimizes charge separation and transport efficiency. The optimized T-C₃Z₁-PBA (SC) achieves exceptional photothermal catalytic performance, demonstrating a CO₂ conversion rate of 126.0 mmol gcat⁻¹ h⁻¹ with 98.8% CO selectivity under 350 °C light irradiation, while maintaining robust stability over 50 h of continuous operation. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) investigations have identified COOH* as a critical reaction intermediate and elucidated that photoexcitation accelerates charge carrier dynamics, thereby substantially promoting the conversion of key intermediates (CO₂* and CO*) and overall reaction kinetics. This research provides insights for engineering high-performance heterostructured catalysts by controlling interfacial and electronic structures. Full article

The influence of structural water in alumina (Al₂O₃) and silica (SiO₂) coated titanium dioxide (TiO₂) pigments on the photodegradation behavior of polypropylene (PP) composites was investigated. Four commercial rutile TiO₂ pigments with varying surface inorganic coatings were incorporated into PP plaques and subjected to accelerated UV weathering to simulate outdoor exposure. Photodegradation was assessed through gloss retention measurements, the carbonyl index (CI), and stress at break retention, while pigment morphology and composition were analyzed using transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). Surface charge and water content were determined through the zeta potential (ζ), Karl Fischer titration, thermogravimetric analysis (TGA), and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). The results showed that low-alumina coating alone led to the lowest photodegradation resistance, the highest CI, and the lowest stress at break retention. In contrast, increasing alumina content enhanced photostability, reaching its maximum for combined alumina–silica coatings, which mitigated electron–hole pair migration. PP composites with high alumina–silica-coated TiO₂ exhibited higher gloss retention (36%) compared to low-alumina samples (21%). Furthermore, statistical analysis using ANOVA revealed significant differences in coating content and ζ potential among the pigment grades. These findings provide novel insights into oxide-water interactions and the impact of structural water on the photodegradation of polymer composites. Full article

In this work, we report the synthesis of perovskite-type Ba-doped LaFeO₃ (La_1−xBa_xFeO₃, x = 0.00, 0.02, 0.04, and 0.06) nanofibers (NFs) using the electrospinning method. The synthesized La_1−xBa_xFeO₃ materials have a fibrous structure with an average fiber diameter of 250 nm. The fibers, in turn, consist of smaller crystalline particles of 20–50 nm in size. The sensor properties of La_1−xBa_xFeO₃ nanofibers were studied when detecting 20 ppm CO, CH₄, methanol, and acetone in dry air in the temperature range of 50–350 °C. Doping with barium leads to a significant increase in sensor response and a decrease in operating temperature when detecting volatile organic compounds (VOCs). The process of acetone oxidation on the surface of the most sensitive La_0.98Ba_0.02FeO₃ material was studied using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and temperature-programmed desorption in combination with mass spectrometry (TPD-MS). A mechanism for the sensor signal formation is proposed. Full article

The existence of historical pigments databases is important to speed up cultural heritage research. Knowledge of their chemical composition and their manufacture contributes to the study of art history and helps develop accurate conservation-restoration strategies. In this study, a total of nineteen pigments, among which we find silicates (Egyptian blue, natural and synthetic blue ultramarine, green earth and chrysocolla), oxides (natural and synthetic hematite, red and yellow natural ochres, and chromium green), carbonates (natural and synthetic azurite, natural and synthetic malachite, and white lead), sulphides (natural and synthetic cinnabar, and orpiment) and acetates, (verdigris) have been characterized by Fourier Transform Infrared-Spectroscopy in Attenuated Total Reflection (ATR-FTIR) and Diffuse Reflectance (DRIFT) modalities. Considering the latter, there is still a great deal of uncertainty in the interpretation of the different IR vibrational bands. Therefore, a comparative study between these two techniques has been carried out to highlight the potential of DRIFT spectroscopy as a portable and non-destructive technique that allows the differentiation and characterization of historical pigments in the field of cultural heritage. Before performing FTIR analysis, pigments were analysed using X-ray diffraction (XRD) to detect impurities and/or additives in the pigments. Differentiation between natural and synthetic pigments was possible due to the identification of impurities in natural pigments, and manufacture-related compounds or additives in synthetic pigments. Results obtained in this study have proven DRIFT to be a very useful analytical technique for in situ characterization of heritage materials. This study serves as an initial step in clarifying the challenges and uncertainties associated with interpreting spectra obtained through the DRIFT modality. However, the use of other complementary analytical techniques is required. Full article

The conversion of CO₂ into light olefins over bifunctional catalysts is a promising route for producing high-value-added products. This approach not only mitigates excessive CO₂ emissions but also reduces the chemical industry’s reliance on fossil fuels. Among bifunctional catalysts, ZnZrO_x is widely used due to its favorable oxide composition. In this work, ZnZrO_x solid solution was synthesized by calcining an MOF precursor, resulting in a large specific surface area and a small particle size. Characterization studies revealed that ZnZrO_x prepared via MOF calcination exhibited an enhanced CO₂ activation and H₂ dissociation capacity compared to that synthesized using the co-precipitation method. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed that CO₂ adsorption on ZnZrO_x led to the formation of carbonate species, while HCOO* and CH₃O* intermediates were generated upon exposure to the reaction gas. When ZnZrO_x was combined with SAPO-34 molecular sieves under reaction conditions of 380 °C, 3 MPa, and 6000 mL·g_cat⁻¹·h⁻¹, the CO₂ conversion reached 34.37%, with a light olefin yield of 15.13%, demonstrating a superior catalytic performance compared to that of the co-precipitation method. Full article

Selective catalytic reduction of NO_x with H₂ (H₂-SCR) is crucial for eliminating NO_x emissions from hydrogen internal combustion engines (H₂-ICE). Although 1 wt.% Pt/SSZ-13 (Pt/SZ) is a promising H₂-SCR catalyst, it faces challenges such as a narrow operating window and low N₂ selectivity. Herein, the effects of WO₃ on improving the H₂-SCR performance of Pt/SZ was investigated. Results showed that incorporating 5 wt.% WO₃ significantly widened the temperature window for 80% NO_x conversion and enhanced N₂ selectivity at 90–180 °C. Several characterizations revealed that electrons transfer from W to Pt, so more active Pt⁰ species were formed on 1 wt.% Pt-5 wt.% W/SZ (Pt-5W/SZ). In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis indicated that more active monodentate nitrates, nitrites, and NH₄⁺ species were generated on Pt-5W/SZ, which are key intermediates for N₂ formation. Consequently, the temperature windows for NO_x conversion (over 80%) and N₂ selectivity (over 70%) were widened by 65 °C and 66 °C, respectively. This work provides insights into the developing H₂-SCR catalysts with broader operating windows and higher N₂ selectivity. Full article

In an O₂-containing environment, achieving efficient selective catalytic reduction of nitrogen oxides (NOx) by carbon monoxide (CO) using non-noble metal catalysts remains a formidable challenge. To balance the catalytic oxidation of CO and the catalytic reduction of NOx, we need to develop a catalyst with strong reductibility and weak oxidizability for the CO selective catalytic reduction of NOx (CO-SCR) reaction in the presence of O₂. In this study, we synthesized the CoCeOx-PVP catalyst via a coprecipitation method and employed various characterization techniques, including BET, SEM, XRD, Raman, XPS, H₂-TPR, and O₂-TPD. The analysis results indicate that the addition of polyvinylpyrrolidone (PVP) alters the surface structure of the catalyst, increases the particle size, and enhances the concentration of surface oxygen vacancies. These structural effects facilitate electron circulation and accelerate the migration of oxygen species, thereby improving the catalytic reduction performance of the catalyst and increasing the conversion rate of NOx. At 250 °C and with 5 vol% O₂, the conversion rates of NOx and CO can attain 98% and 96%, respectively, accompanied by a remarkable N₂ selectivity of 99%. Following a sustained reaction period of 6 h, the conversion efficiencies of both NOx and CO remain above 95%. However, during extended testing periods, as the oxygen vacancies are progressively occupied by O₂, the oxygen vacancies generated through the reduction of NO with CO fall short of sustaining the CO-SCR reaction over the long haul. Subsequently, the oxidation reactions of NO and CO come to dominate, resulting in a decline in the NOx conversion rate. Notably, the CO conversion rate still maintains 100% at this point. Based on the results of in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) experiments, we proposed a reaction mechanism for the CO-SCR process over the CoCeOx-PVP catalyst under O₂-containing conditions. This study provides an effective strategy for the application of non-noble metal catalysts in the field of CO-SCR. Although maintaining long-term activity of the catalyst remains a challenge in the presence of O₂, the catalyst in this study exhibits a slower deactivation rate compared to traditional non-noble metal catalysts. Full article

Nowadays, volatile organic compounds (VOCs) increasingly jeopardize ecosystem sustainability and human well-being. In this study, UiO-66 and its different electron beam (EB) irradiation doses (100, 300, 500 kGy) modified materials supported Pt catalysts, Pt/UiO-66 and Pt/UiO-66-X (X = 100, 300, and 500, representing the irradiation doses), were synthesized, and a series of characterizations were conducted on the samples. On this basis, the effectiveness of these catalysts was evaluated through the degradation of ethyl acetate. The study findings indicated that the sample irradiated at 100 kGy demonstrated superior catalytic performance. Thereafter, extensive tests with regard to water resistance, stability, and cycle performance indicated that the Pt/UiO-66-100 catalyst was characterized by satisfactory reusability and catalytic stability, even when faced with high heat and humidity. Further work with in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and thermal desorption–gas chromatography–mass spectrometry (TD-GC–MS) uncovered the process of degradation of ethyl acetate. This research provides a guideline for the design of high-performance VOC degradation catalysts through EB modification. Full article

Improving the dispersion of Cu_xO species is critical for enhancing the catalytic performance of Cu_xO/CeO₂ catalysts in the preferential oxidation of CO. Herein, the 10Cu_xO/CeO₂ catalyst was synthesized using a combined approach of one-step thermal decomposition and precipitation methods. A series of characterization results indicate that the CeO₂ support we prepared is rich in defect sites, which not only enhance the interaction between CeO₂ and Cu_xO, but also promote the generation of more active Cu⁺ sites while reducing the strength of the Ce−O bond. Raman spectroscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) demonstrated that the weakened Ce–O bonds promote the extraction of lattice oxygen, thereby enhancing the carboxyl reaction pathway. Consequently, the highly dispersed 10Cu_xO/CeO₂ catalyst exhibits remarkably high catalytic activity for the oxidation of CO over a broad operating temperature range (i.e., CO 100% conversion, 95–215 °C). This study represents an important advancement toward the facile synthesis of highly active transition-metal oxide catalysts. Full article

Phthalic acid esters (PAEs), ubiquitous semi-volatile organic compounds (SVOCs) in indoor environments, pose adverse effects on human health. However, their degradation mechanisms and pathways remain unclear. Herein, we developed an efficient photothermal catalyst by introducing defects (oxygen vacancies, O_Vs) on TiO₂ (P25) surfaces via electron beam irradiation technology with different irradiation doses (100, 300, 500, and 700 kGy). The TiO₂ with defects was employed as a support to prepare Pt-TiO₂ catalysts for the photothermal degradation of di (2-ethylhexyl) phthalate (DEMP) and dimethyl phthalate (DMP), two representative PAEs. TiO₂ pre-treated with a 300 kGy irradiation dose supported the Pt catalyst (Pt-Ti-P-300) and presented the optimal catalytic performance for DEMP and DMP degradation. Characterization results confirmed that O_Vs were successfully introduced to the catalysts. Meanwhile, O_Vs induced by electron beam irradiation expanded the light absorption range and improved the generation and separation of photogenerated carriers, which significantly enhanced the catalytic activity of the catalysts for PAE degradation. Importantly, the degradation mechanism and pathway of DMP were further explored by using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and gas chromatography–mass spectrometry (GC-MS). These findings provide important insights into the electron beam irradiation-mediated regulation of catalysts and the photothermal catalytic removal of PAEs in indoor environments. Full article

The water–gas shift (WGS) reaction is one of the most significant reactions in hydrogen technology since it can be used directly to produce hydrogen from the reaction of CO and water; it is also a side reaction taking place in the hydrocarbon reforming processes, determining their selectivity towards H₂ production. The development of highly active WGS catalysts, especially at temperatures below ~450 °C, where the reaction is thermodynamically favored but kinetically limited, remains a challenge. From a fundamental point of view, the reaction mechanism is still unclear. Since specific nanoshapes of CeO₂-based supports have recently been shown to play an important role in the performance of metal nanoparticles dispersed on their surface, in this study, a comparative study of the WGS is conducted on Pt nanoparticles dispersed (with low loading, 0.5 wt.% Pt) on CeO₂ and gadolinium-doped ceria (GDC) supports of different nano-morphologies, i.e., nanorods (NRs) and irregularly faceted particle (IRFP) CeO₂ and GDC, produced by employing hydrothermal and (co-)precipitation synthesis methods, respectively. The results showed that the support’s shape strongly affected its physicochemical properties and in turn the WGS performance of the dispersed Pt nanoparticles. Nanorod-shaped CeO_2,NRs and GDC_NRs supports presented a higher specific surface area, lower primary crystallite size and enhanced reducibility at lower temperatures compared to the corresponding irregular faceted CeO_2,IRFP and GDC_IRFP supports, leading to up to 5-fold higher WGS activity of the Pt particles supported on them. The Pt/GDC_NRs catalyst outperformed all other catalysts and exhibited excellent time-on-stream (TOS) stability. A variety of techniques, namely N₂ physical adsorption–desorption (the BET method), scanning and transmission electron microscopies (SEM and TEM), powder X-ray diffraction (PXRD) and hydrogen temperature programmed reduction (H₂-TPR), were used to identify the texture, structure, morphology and other physical properties of the materials, which together with the in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) and detailed kinetic studies helped to decipher their catalytic behavior. The enhanced metal–support interactions of Pt nanoparticles with the nanorod-shaped CeO_2,NRs and GDC_NRs supports due to the creation of more active sites at the metal–support interface, leading to significantly improved reducibility of these catalysts, were concluded to be the critical factor for their superior WGS activity. Both the redox and associative reaction mechanisms proposed for WGS in the literature were found to contribute to the reaction pathway. Full article