Catalytic Activity Of Catalysts Research Articles

Preparation and NH3-SCR catalytic performance of CeTiOx catalysts with different pore structures

To investigate the influence of pore structure on the catalytic activity of catalysts, four catalysts including three-dimensionally ordered macroporous-mesoporous (3DOM-m) CeTiOx, three-dimensionally ordered macroporous (3DOM) CeTiOx, three-dimensionally ordered mesoporous (3DOm) CeTiOx and disordered mesoporous (DM) CeTiOx were synthesized by the sol-gel method. The NH3-SCR denitration testing results show that the performance of the catalysts with different pore structures follows the sequence of 3DOM-m CeTiOx>3DOm CeTiOx>3DOM CeTiOx>DM CeTiOx, and the 3DOM-m CeTiOx shows an excellent catalytic activity, with more than 90% NO conversion in the range of 250–400 °C at a GHSV of 60000 h−1. The characterization of catalysts by XRD, SEM, BET, NH3-TPD and in-situ DRIFTS indicates that the surface area is not the dominant factor determining the catalytic activity of CeTiOx. 3DOM-m CeTiOx has a highly ordered macroporous-mesoporous structure and abundant Bronsted acidic sites, thereby improving the denitrification activity. The NH3-SCR reaction over the 3DOM-m CeTiOx mainly follows the L-H and E-R mechanisms.

Carbon Monoxide and Propylene Catalytic Oxidation Activity of Noble Metals (M = Pt, Pd, Ag, and Au) Loaded on the Surface of Ce0.875Zr0.125O2 (110)

With the advances in engine technology, the exhaust gas temperature of automobiles has further reduced, which in turn leads to an increase in the emissions of carbon monoxide (CO) and hydrocarbons (HCs). In order to understand the influence of CeO2-based catalysts loaded with different noble metals on the catalytic oxidation activity of CO and HCs, this study constructed catalyst models of Ce0.875Zr0.125O2 (100) surfaces loaded with Pt, Pd, Ag, and Au. The electronic density and state density structures of the catalysts were analyzed, and the reaction energy barriers for CO oxidation and C3H6 dehydrogenation oxidation on the catalyst surfaces were also calculated. Furthermore, the activity sequences of the catalysts were explored. The results revealed that after loading Pt, Pd, Ag, and Au atoms onto the catalyst surfaces, these noble metal atoms exhibited strong interactions with the catalyst surfaces, and electron transfer occurred between the noble metal atoms and the catalyst surfaces. Loading with noble metals can enhance the catalytic activity of CO oxidation, but it has little effect on the dehydrogenation oxidation of C3H6. Of the different noble metals, loading with Pd exhibits the best catalytic activity for both CO and C3H6 oxidation. This study elucidated the influence of noble metal doping on the catalytic activity of catalysts at the molecular level, providing theoretical guidance for the design of a new generation of green and efficient catalysts.

Cobalt catalyst encapsulated by N-doped carbon for selective hydrogenation of aldehyde to alcohol

Furfuryl alcohol is an important industrial chemical and an intermediate for the synthesis of other high-value products. Here, an explosion-assisted strategy was developed to synthesize nitrogen-doped carbon-encapsulated cobalt nanoparticles catalyst Co-NC. The selective hydrogenation of furfural to furfuryl alcohol can be achieved over Co-NC in aqueous solution successfully. The presence of cobalt nitrate enhanced the explosion process which promoted its decomposition in turn. The high-temperature reduction process accelerated the derivation of carbon nitride into N-containing carbon encapsulating on cobalt nanoparticles. The N-containing coating improves the hydrophilia and catalytic activity of catalyst, thus achieving the selective hydrogenation of aldehydes in aqueous solution.

One-pot synthesis of acrylic acid from glycerol over SBA-15 supported heteropoly acid catalysts: Influence of mesoporosity and acidity

Heteropoly acids (HPAs) of the Keggin type exhibit substantial Brønsted acidity and are commonly utilized as acid catalysts, particularly in acrylic acid synthesis via glycerol oxydehydration. The primary goal of this research is to comprehensively assess the morphological and physicochemical properties of SBA-15 supported HPAs (H4SiW12O40.xH2O, H3PW12O40.xH2O, and H3PMo12O40.xH2O). The synthesized catalysts were characterized via physisorption analysis, XRD, SEM, FT-IR, NH3-TPD, and H2-TPR. Furthermore, the catalyst's catalytic activity in acrylic acid synthesis via single-step liquid phase glycerol oxydehydration was evaluated by correlating its characteristics with glycerol conversion and acrylic acid yields. The PW/SBA-15 catalyst exhibited the best performance, with the highest acrylic acid yield reaching 17.5% at 87.8% glycerol conversion. Given that the partial oxidation of acrolein to acrylic acid necessitates an optimal level of redox properties, the superior performance of PW/SBA-15 was characterized by high acid sites and moderate oxidative capabilities.

Two‐Dimensional BiOBr Nanosheets Coupled with FeOOH Quantum Dots as Composite Photo‐Fenton Catalysts for Organic Pollutant Degradation under Visible Light

AbstractFeOOH quantum dots (QDs) were successfully anchored on 2D BiOBr nanosheets as composite photo‐Fenton catalysts by a simple precipitation and impregnation method. Using Rhodamine B (RhB) as an organic dye model, the photo‐Fenton catalytic activity of the composite catalyst was significantly higher than that of BiOBr and FeOOH. Among them, 1.8 % FeOOH/BiOBr has the highest photo‐Fenton catalytic activity. The main reason is that the interface effect between FeOOH and BiOBr can enable photogenerated electrons to rapidly transfer from the surface of BiOBr to FeOOH to participate in the Fe3+/Fe2+ cycle. Meanwhile, the quantum size of FeOOH increases the density of active sites on the surface of the composite catalyst. The influence of external factors on the catalytic activity of the catalyst was also verified. Finally, the electron transfer direction and main active species (h+, ⋅O2−) of the composite catalyst were discussed by electrochemical analysis and radical trapping experiments, and a reasonable catalytic degradation mechanism was proposed.

Role of the surface chemistry of carbon xerogel-based supports and Cu catalysts in the oxidation reaction of glycerol

Carbon xerogel with pore size of about 10 nm were obtained using the sol–gel method and applying different thermal treatments. Catalysts were prepared depositing 3 wt% of copper on the xerogel. The catalytic activities of catalysts and supports were evaluated in the selective oxidation of glycerol (GLY). The supports showed good conversion and selectivity to glyceric acid (GA) and lactic acid (LA), with higher preference to GA. For the catalysts, the conversions were slightly higher, and the order of selectivity changed, benefiting the production of LA. Changes in selectivity between supports and catalysts were mainly associated with the different acid-base surface characteristics and the presence of the Cu domains in the catalysts. In the supports, even if the thermal treatment applied modifies the type and content of oxygenated functional groups (OFG) on the surface, predominates a superficial acid character, addressing the selectivity to GA. On the other hand, the basic character of the catalysts due to the Cu presence and the large metallic domain sizes favoured the production of LA. During the recycle test, supports and catalysts showed a decrease in catalytic activity. After three recycles, the catalytic performances of catalysts and supports were similar due to metal leaching.

Insights into influence of CeO2 crystal structure effects on hydrothermal hydrogenation for palmitic acid over Ni/CeO2 catalysts

In recent years, upgrading renewable bio–oil to hydrocarbon fuels has received increasing attention. It is crucial to develop a catalyst with high activity, low cost, and high hydrothermal stability for bio–oil upgrading. In this work, the non-noble metal Ni/CeO2 is proved to be a potential catalyst for hydrothermal hydrogenation of palmitic acid (model compound of microalgae based bio–oil). The effect of the crystal structure of the support on the hydrothermal hydrogenation activity of palmitic acid is investigated for the first time. The research results indicate that the catalytic activity of catalysts with different support crystal structures is in the following order: Ni/CeO2–r (nanorods) > Ni/CeO2–c (nanocubes) > Ni/CeO2–p (nanoparticles). The excellent activity of Ni/CeO2–r is attributed to its larger specific surface area, higher defect and oxygen vacancy concentration, and the formation of more Ni0 due to strong metal − support interaction (SMSI). After optimization of conditions at 300 °C, 98.9 % conversion and 92.4 % alkanes yield are obtained over the Ni/CeO2–r. In addition, the coating structure formed by the SMSI provides good hydrothermal stability for the catalyst.

D-Electron tuned CoMoP for enhance 5-hydroxymethylfurfural oxidation and HER

Implementing d-electron complementation by atomic doping can improve the catalyst's catalytic activity, but the exact active sites and detailed mechanism of this catalyst remain ambiguous in the oxidation of 5-hydroxymethylfurfural (HMFOR) and hydrogen evolution reactions (HER). Here, CoMoP nanoplates are successfully fabricated via the 3d orbital filling characteristics. It is found that Mo can disorder the coordination environment of Co, promoting surface electro-generation of MoOx and CoOOH species. Meanwhile, CoP can only oxidize the formyl group to produce carboxylate, while MoOx and CoOOH species are required to oxidize the hydroxyl group. Additionally, the introduction of Mo makes the lattice expansion of CoP leading to Co d-band center up-shift, benefiting to hydrogen adsorption for enhancing HER activity. Therefore, selective production of 5-hydroxymethyl-2-furan carboxylic acid (HMFCA) and 2,5-furan dicarboxylic acid (FDCA) and promotion of HER reaction activity can be achieved through d-electron tuning.

Tribocatalytic activity on Ba(Ti0.95Zr0.05)O3 surfaces: The role of oxygen vacancies and the aging effect

This study explores the potential of tribocatalysis, a resource-efficient degradation technique, using ferroelectric perovskite-type Ba(Ti0.95Zr0.05)O3 (BZT) with oxygen vacancies as a catalyst. The catalysts, synthesized via a standard solid-state method, were analyzed using XPS and EPR to confirm the presence of oxygen vacancies. Their electrical properties were evaluated through UV–vis diffuse reflectance spectra and Mott–Schottky plots. Freshly prepared BZT catalysts demonstrated a 92% degradation of Rhodamine B (RhB) within 20 h, achieving a reaction rate constant (K) of 0.114 h−1. However, aging significantly reduced RhB degradation, with de-aging failing to restore initial activity. The study attributes the catalyst's catalytic activity and aging issues to the oxygen vacancies, acting as shallow donor states. It also highlights the benefits of tribocatalysis due to electron accumulation at the surface from friction-generated contact, emphasizing the critical role of oxygen vacancies in catalytic degradation and long-term catalyst stability.

The catalytic activity of manganese oxide catalysts for the toluene oxidation process

Manganese oxide catalysts were prepared by several preparation methods, such as hydrothermal, sol-gel method, and characterized by XRD, BET, H2-TPR, SEM-EDS, and FT-IR. The catalytic activities of catalysts were evaluated through the toluene reaction at the temperature range of 150 oC – 400 oC. Among the catalysts, the @ MnO2 150 catalyst exhibited the highest catalytic activity. It could completely convert toluene into CO2 at 300 oC. The larger specific surface area and lower reduction temperature enhance the higher activity of the @ MnO2 150 catalyst. Thus, the @ MnO2 150 catalyst is chosen to study in the subsequent research.

Toluene combustion over Co3O4-CNTs/PSSF catalysts and investigation of the effects of acid treatment on catalytic activity

BackgroundCo3O4 shows potential as a cost-effective alternative to precious metal catalysts for VOCs catalytic combustion. However, its catalytic activity requires further enhancement. MethodsA new type of paper-like carbon nanotube membrane composite (CNTs/PSSF) was used as a support to prepare Co3O4-CNTs/PSSF catalysts by metal-organic vapor deposition (MOCVD) and impregnation method (IM) respectively for toluene combustion. Besides, the effects of acid treatment to support on the catalytic activity were investigated. Various characterization techniques, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), and oxygen temperature-programmed desorption (O2-TPD), were employed to evaluate the effects of different preparation methods and acid treatment on the structure and catalytic performance mechanism of Co3O4-CNTs/PSSF. Significant findingsThe preparation method significantly affects the catalyst's properties and catalytic activity. Compared with IM, the MOCVD-prepared catalysts show stronger coordination of carbon nanotubes, resulting in more oxygen vacancies and surface active oxygen. Additionally, oxygenous groups introduced by HNO3 form Co-O-C linkage between Co and CNTs, promoting oxygen vacancies and enhancing surface active oxygen content, thereby dramatically improving the catalyst's catalytic activity, especially for HIM-10 whose T90 is reduced by 140 °C. This work provides insights for enhancing the catalytic combustion activity of cobalt oxide.

Constructing Molybdenum Phosphide@Cobalt Phosphide Heterostructure Nanoarrays on Nickel Foam as a Bifunctional Electrocatalyst for Enhanced Overall Water Splitting.

The construction of multi-level heterostructure materials is an effective way to further the catalytic activity of catalysts. Here, we assembled self-supporting MoS2@Co precursor nanoarrays on the support of nickel foam by coupling the hydrothermal method and electrostatic adsorption method, followed by a low-temperature phosphating strategy to obtain Mo4P3@CoP/NF electrode materials. The construction of the Mo4P3@CoP heterojunction can lead to electron transfer from the Mo4P3 phase to the CoP phase at the phase interface region, thereby optimizing the charge structure of the active sites. Not only that, the introduction of Mo4P3 will make water molecules preferentially adsorb on its surface, which will help to reduce the water molecule decomposition energy barrier of the Mo4P3@CoP heterojunction. Subsequently, H* overflowed to the surface of CoP to generate H2 molecules, which finally showed a lower water molecule decomposition energy barrier and better intermediate adsorption energy. Based on this, the material shows excellent HER/OER dual-functional catalytic performance under alkaline conditions. It only needs 72 mV and 238 mV to reach 10 mA/cm2 for HER and OER, respectively. Meanwhile, in a two-electrode system, only 1.54 V is needed to reach 10 mA/cm2, which is even better than the commercial RuO2/NF||Pt/C/NF electrode pair. In addition, the unique self-supporting structure design ensures unimpeded electron transmission between the loaded nanoarray and the conductive substrate. The loose porous surface design is not only conducive to the full exposure of more catalytic sites on the surface but also facilitates the smooth escape of gas after production so as to improve the utilization rate of active sites. This work has important guiding significance for the design and development of high-performance bifunctional electrolytic water catalysts.

Poisoning mechanism of different Cd precursors on Fe-Ce/TiO2 catalyst for selective catalytic reduction of NOx with NH3

As one of the most harmful heavy metals, Cd can present in many chemical forms in real flue gas and may deactivate the SCR catalysts, but the poisoning mechanism of different Cd species over the Fe-Ce/TiO2 catalysts remains unclear. Therefore, in our work, Fe-Ce/TiO2 catalyst is prepared and doped with Cd(NO3)2, CdCl2, and CdSO4, respectively, aiming to investigate the effect of different Cd precursors on the catalytic performance, physicochemical properties, and poisoning mechanisms of Fe-Ce/TiO2 catalyst. The results demonstrate that different Cd precursors exert different influences on the catalytic activity of the catalyst and the deactivation sequence is CdSO4 <Cd(NO3)2 <CdCl2. The doping of Cd decreases the specific surface area, promotes the grain growth of active species, and results in the aggregation of surface active species to varying degrees. Although the total H2 consumption of Cd poisoned catalysts is enhanced, they are not originated from more amounts of surface active species and thus it does not contribute to the redox cycles and catalytic activity of catalysts. The doping of Cd(NO3)2 decreases the surface acidity of catalysts, while CdCl2 and CdSO4 promote surface acidity, but the adsorbed NH3 over CdCl2 poisoned catalyst is unreactive. In addition, both Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms are involved in the SCR reaction over the Fe-Ce/TiO2 catalyst and different Cd poisoning makes no change to the reaction mechanism.

Effect of pH on Microstructure and Catalytic Oxidation of Formaldehyde in MnO2 Catalyst

Layered δ-MnO2 catalysts were prepared using the one-step redox method in precursor solutions with five different pH values (pH = 7, 9, 11, 13, and 14). The effects of pH on the physical properties and catalytic activity of the catalyst were investigated through XRD, SEM, TEM, BET, XPS, H2-TPR, and HCHO degradation tests at room temperature. The results showed that the layer spacing, manganese vacancy content, Mn4+/Mn3+ ratio, and surface-reactive oxygen species content of MnO2 increased with the increase in pH value in the alkaline range. When the catalyst was prepared at pH = 13, the above characteristics of the catalyst reached the optimal value which contributed to the high catalytic activity. Combined with the related characterization results, it was proved that changing the pH can affect the degree of oxidation in the catalyst synthesis process, increase the number of active oxygen and the oxygen mobility of the catalyst, and effectively improve the catalytic activity of the manganese dioxide catalyst for HCHO. This work represents a giant step toward the preparation of an effective catalyst for practical applications of HCHO removal at room temperature at a low concentration and high velocity.

Effects of H2/O2 and H2/O3 gases on PtMo/C cathode PEMFCs performance operating at different temperatures

This study reported the activity of catalysts synthesized from platinum and molybdenum alloys in different atomic ratios and used as cathode electrocatalysts in the PEMFC. The structural properties of PtMo/C and Pt/C catalysts were analyzed by XRD analysis. The composition and distribution of these alloys in Vulcan XC-72R Carbon were determined by SEM and EDX techniques. CV studies assessed electrochemical properties such as ORR and ECSA activity. The performance of PEMFC cathodes that supplied pure hydrogen and oxygen was examined using polarization curves at different temperatures. Another way to improve the cathodic reaction is to use ozone as a potent oxidizing agent. It was measured that the OCV of the H2/O3 PEM fuel cell was 1.60 V, much greater than the open circuit voltage of the traditional H2/O2 PEM fuel cell. The PtMo/C catalyst achieved its highest power density of 137 mWcm−2 at 70 °C, 128 mWcm−2 at 60 °C, 101 mWcm−2 at 50 °C, and 85 mWcm−2 at 40 °C when exposed to H2/O2. As the temperature of the cell was raised, it was seen that the catalyst's catalytic activity increased.The maximum power density was detected to be inversely related to the rise in temperature when ozone was used. At low current densities, however, ozone was observed to greatly boost activation polarization.

Aluminosilicates Catalysts Synthesis from Low-Grade Indonesian Kaolin for the Acetalization Reaction

Aluminosilicate and ZSM-5 catalyst were synthesized from local materials, low-grade Indonesian kaolin. High quartz impurities content in the low-grade kaolin was successfully reduced by the consecutive treatment process including washing, centrifugation, and Fe3+ treatment. All the synthesized catalyst showed mesoporous structure with pore diameter around 3.5 nm. The catalytic activity was investigated in the acetalization of 3,4-dimethoxybenzaldehyde and propylene glycol, then the effect of a different base (TPAOH and NaOH) and Fe3+ addition in the treatment process to the catalytic activity was discussed. The catalytic activity of the aluminosilicate catalyst outperforms the ZSM-5. Interestingly, it is found that the catalytic activity of the catalyst can be enhanced by addition of Fe3+ in the aluminosilicate, with enhanced the conversion from 32.2% to 81.6%, whereas Fe3+ addition to ZSM-5 showed slightly increased conversion value from 0% to 3.65%. All catalysts showed high selectivity of 100% of the reaction product 2-(3,4-dimethoxy-phenyl)-4-methyl-1,3-dioxolane.

Enhancing the reusability of hydroxyapatite by barium modification for efficient isomerization of glucose to fructose in ethanol

The application of synthetic catalysts to displace costly isomerases for glucose isomerization to fructose has been a long-standing goal in biomass valorization, but current catalysts generally suffer from inferior stability and reusability. Here we show that the combination of barium modified hydroxyapatite (Ba/HAP) as catalyst with ethanol as solvent enables highly efficient and selective isomerization of glucose to fructose, affording fructose yield of 35.4% with selectivity up to 93.5% at high glucose loading (10 wt%). Moreover, the Ba/HAP catalyst was reused with high recovery rate and the leaching of ions was greatly inhibited. The composition, structure and catalytic activity of catalyst can be almost completely restored after calcination. Density functional theory simulations revealed that the formation of relatively stable BaCa6(PO4)4O phase is beneficial to the improved catalyst stability. Simultaneously achieving high reaction efficiency and good catalyst reusability in green solvent, our study is an important step towards sustainable catalysis.

Surface engineered active Co3+ species in alkali doped Co3O4 spinel catalyst with superior O2 activation for efficient CO oxidation

CO oxidation is one of the most extensively investigated fields of research as it takes prime importance in environmental fortification and is highly challenging to explore efficient heterogeneous catalysts to achieve effectual conversion. In the present work, Co3O4 and alkali metal-doped Co3O4 spinel materials were obtained by the co-precipitation method and employed as suitable catalysts for CO oxidation. The catalysts were prepared by calcining the precipitated hydroxides of Co at 300°C, and 800°C (with and without the presence of water vapor) in the air atmosphere. The synthesized materials were characterized by powder X-ray diffraction, N2-sorption analysis, H2-TPR, SEM, and XPS techniques. Then the catalytic activity of catalysts is evaluated for CO oxidation using molecular O2 as an oxidizing agent. The effect of thermal treatment and also the role of alkali metal in CO oxidation are studied. The promotional effect of alkali (Li, Na, and K) in Co3O4 materials was observed with higher CO conversion, where the influence of Li ions in the Co3O4 catalyst was far greater than in other doped catalysts. Definite characteristics, nature of alkali-doped catalysts, and oxidative influence involved in CO oxidation reaction mechanism were carefully studied. In a general perspective, this work shows the influence of surface properties of alkali ion-doped Co3O4 spinel catalysts that consequently control the reactivity toward CO oxidation.

Morphology design and synthesis of magnetic microspheres as highly efficient reusable catalyst for organic dyes

Precise synthesis of magnetic particles that surface chemistry spanning is critically needed for the fundamental research. We reported a new seed emulsion interfacial polymerization, which precisely synthesized magnetic polymer particles spanning from sulfonated porous magnetic microspheres to topology structured magnetic microspheres (TPMMs). By varying the degree of cross-linking, the type of monomer, several types of magnetic polymer particles with different morphology were obtained. Then silver nanoparticles (NPs) were precipitated in situ on the surface of topology structured magnetic microspheres as catalyst (Ag@TPMMs). To estimate the catalytic activity, the reduction experiments of Rhodamine B (RhB) and 4-nitrophenol (4-NP) were studied. These toxic dyes can be reduced in a very short time, and the apparent rate coeffcients of RhB and 4-NP were 0.03156 s−1 and 0.0286 s−1 respectively, which indicated that they had a good catalytic performance. When the catalyst was used 5 cycles, the catalytic activity of catalyst was still high. The potential applications of TPMMs will be very useful in labeling, tracking, protein separation and other biomedical fields.

Green synthesis of pistachio shell-derived biochar supported cobalt catalysts and their catalytic performance in sodium borohydride hydrolysis

Pistachio shell-derived biochar supported cobalt catalysts were synthesized by using a modified impregnation-chemical reduction method. Polydopamine (PDA) and tannic acid (TA) were used as reducing and functionalizing agents. The effect of modification treatment was investigated on the physicochemical and catalytic properties. The peaks observed in XRD patterns belonged to biochar and cobalt. The surface area, total pore volume and pore diameter values of Co-PDA@BC catalyst were determined as 268 m2/g, 0.262 cm3/g and 3.03 nm, respectively. These values higher than that of Co-TA@BC catalyst. FTIR spectra exhibited bands representing the biochar structure. XPS spectra showed that cobalt was embedded in the support structure in metallic and oxide form. The use of PDA improved structural properties and catalytic activity of catalyst. The maximum hydrogen generation rate and activation energy for Co-PDA@BC was determined as 25 mL min−1gcat−1 and 31.3 kJ mol−1, respectively.