Surface Acid Sites Research Articles

Controlling the surface properties of HY zeolite by Ce doping to achieve enhanced catalytic desulfurization

ABSTRACT CeHY molecular sieve adsorbents have been prepared by incipient wetness impregnation and subjected to a comprehensive characterization. X-ray diffraction (XRD) analysis was employed to determine the adsorbent crystalline structure. The specific surface area was measured using the BET method to evaluate adsorption capacity. Scanning electron microscopy (SEM) was utilized to assess surface morphology. The combined characterization measurements allow a direct correlation of adsorption with CeHY structure in order to optimize performance. At a Ce loading of 16%, cerium oxide particles on the external surface blocked some adsorbent pores. The content and nature of surface acid sites were determined by py-FT-IR measurements, and the adsorption-desulfurization performance was evaluated using fixed-bed breakthrough curves with chromatographic analysis. At a Ce loading of 6%, the adsorption-desulfurization efficiency was relatively high. When the ratio of total surface Brönsted (B) to Lewis (L) acidity decreased, adsorption-desulfurization performance was enhanced. An appropriate level of Ce is required to improve overall performance where a high Ce loading is detrimental due to the formation of cerium oxide particles on the adsorbent surface.

Synthesis of in-plane Mo2C/MoO3 heterostructures by a novel spatial-confined partial oxidation approach for enhanced TEA sensing.

In-plane heterostructures exhibit extraordinary chemical and electron transfer properties, which have received remarkable research attention. However, the synthesis of an in-plane Mo2C/MoO3 heterostructure has been rarely reported, and the deep investigation of the effect of its fine structure on reactivity is of great significance. Notably, the in-plane heterostructures endow the material with abundant grain boundaries, which facilitate the formation of surface acid sites and active oxygen species, thus contributing to the sensing performance. Our work provides a promising platform to design in-plane heterostructures for various advanced applications.

Post-vulcanization combined with magnetic modification of sulfonated biochar as heterogeneous fenton catalyst for tetracycline degradation

Although the Fenton reaction has shown remarkable effectiveness in degrading antibiotic contamination in water bodies, its strict pH dependence has limited its wide practical application. In this study, a novel magnetic biochar material with dual functions of adsorption and catalysis was successfully synthesized by carbonization of the shell of blue flower blue with concentrated sulfuric acid through sulfide and magnetic modification. The innovation of this material is its ability to overcome the recycling limitations of traditional catalysts while achieving efficient reactions in the pH range of 3–11. In particular, the introduction of sulfur promotes a stable cycle of Fe(II)/Fe(III) in the material, thereby enhancing its catalytic properties. The porous structure of the sulphonated jacaranda hull and its successful loading of sulfur and iron were revealed by SEM, FTIR, XRD, and XPS analysis. The experimental results showed that under the conditions of S-Fe3O4@JSS dosage of 0.2 g/L, hydrogen peroxide concentration of 10 mM, initial pH value of 5, and initial tetracycline concentration of 50 mg/L, the optimal degradation rate of tetracycline was as high as 85.85 %. The mechanism analysis shows that hydroxyl radical plays a key role in this reaction system because S-Fe3O4@JSS not only releases Fe(II) but also catalyzes hydrogen peroxide with the introduction of surface acidic sites and sulfur elements, which increases the free radical yield and accelerates the tetracycline degradation process. This study provides a new efficient and stable method to solve the problem of antibiotic pollution treatment in water.

Boosting CO2 photoreduction to acetic acid via the van der waals heterostructures of monolayer Nb2O5 modified TiO2 nanotubes

Photoreduction of CO2 to hydrocarbons encounters two significant challenges: low product yields and poor selectivity. Furthermore, the difficulty of C-C coupling reactions hinders the formation of higher-value two-carbon products. This paper presents a strategy to address these challenges by fabricating a van der Waals heterostructure photocatalyst through the surface modification of TiO2 nanotubes (TNTs) with monolayer Nb2O5, denoted as 3 %Nb2O5/TNTs. Compared with TNTs, the acetic acid yield of heterostructures reached 28.4 μmol gcat-1h−1, and the selectivity rose from 48 % to 69 %. The van der Waals heterostructures reduced the photogenerated electron-hole recombination, extending the lifetime of charge carriers. The reduction of resistance and the presence of built-in fields accelerated the migration of charge carriers, thereby showing an enhanced photocatalytic performance. Surface modification of monolayer Nb2O5 promoted the activation adsorption of CO2 to CO2·-, facilitating the following C-C coupling reaction. Furthermore, its surface acidity sites modulated the hydrogenation reactions following C-C coupling, thereby increasing both the yield and selectivity of acetic acid.

Accurate location of Ni and W active sites in hierarchical zeolite catalyst for the conversion of cellulose to alcohols

The process of converting cellulose into short-chain alcohols is a critical component of biomass valorization. In this study, we utilized an anion-cation co-directed hydrothermal method and wet impregnation to synthesize a hierarchical MFI zeolite with isolated Ni and W sites. We employed linear correlation analysis to evaluate the influence of pore size, site accessibility, and acidity on product selectivity. Balancing hydrogenation and acidic sites on the catalyst enhanced retro-aldol condensation and hydrogenation during cellulose conversion. Surface acidic sites accelerated glucose retro-aldol condensation, while micropore acidic sites aided in ethylene glycol hydrogenolysis. The close proximity of Ni and W facilitated high selectivity and yield of ethanol through bimetallic synergy. This research presented a novel strategy for preparing hierarchical zeolites with isolated metal sites and provides clarity on the cooperative roles of active sites in Ni-W bimetallic catalysts for cellulose conversion.

Insight into NH3-SCR and H2O/SO2 resistance of Ce modified iron-based catalysts with the presence of arsenic

The mechanism of denitrification and arsenic poisoning during the selective catalytic reduction of NOx with ammonia using a cerium-modified iron-based catalyst was investigated through fixed bed activity tests and catalyst characterization. The results demonstrated that cerium formed a solid solution with Fe, and enriched the surface acid sites of the catalyst. Furthermore, cerium inhibited the arsenic-iron interaction, thereby protecting the active sites of the catalyst. After 6 h of arsenic poisoning, the NOx conversion of 0.1Ce catalyst decreased by only about 30 % of that of Fe2O3 catalyst. The cerium-modified iron-based catalyst exhibited significantly better H2O resistance than the Fe2O3 catalyst at 300 °C, and increased as the temperature rose·H2O adsorbed onto the Lewis acid sites on the catalyst surface, converting them into Brønsted acid sites, which promoted arsenic adsorption and oxidation on the surface, thereby greatly reducing adsorption activity of the catalyst. In the presence of SO2 and As2O3 in the flue gas, the denitrification efficiency of the catalyst further decreased, though the reduction is less pronounced than in the presence of H2O and As2O3 alone, and shows a negative correlation with SO2 concentration.

Unraveling the opposite behaviors of Pt/MOx catalysts for toluene and o-xylene mixture oxidation: Modulating mixing effect by optimization supports

Actual industrial emissions usually contain multiple aromatic VOCs, but little is known about adsorption and oxidation behaviors of multicomponent aromatic VOCs over catalysts, which limits the practical application of catalytic oxidation technology. Herein, the adsorption and oxidation of toluene and o-xylene mixture generated during paint production over Pt-based supported catalysts (Pt/NiO, Pt/Co3O4, Pt/Nb2O5 and Pt/CeO2) were investigated. Pt/Nb2O5 and Pt/CeO2 catalysts significantly promoted the oxidation of mixture. However, Pt/NiO and Pt/Co3O4 catalysts exhibited more difficulties in degrading mixed VOCs. Characterization results revealed that Pt/NiO and Pt/Co3O4 possessed higher percentage of surface adsorbed oxygen. Pt/Nb2O5 and Pt/CeO2 had more surface lattice oxygen, Pt0 species and acid sites. The weak competitive adsorption over Pt/Nb2O5 and Pt/CeO2 catalysts might be related to their acidic and electronic properties. In situ experiments proved that surface adsorbed oxygen and surface lattice oxygen of Pt/CeO2 could oxidize toluene and o-xylene simultaneously at lower temperature. However, the depleted oxygen species on Pt/Co3O4 could not be replenished in time due to the strong competitive adsorption and different oxidation mechanisms. This study uncovers the mixing effect of toluene and o-xylene over Pt/MOx catalysts, which provides a guiding direction towards the development of catalysts for efficient degradation of multicomponent VOCs.

Ultra-efficient Ru and Nb Co-Modified CeO2 Catalysts for Catalytic Oxidation of 1,2-Dichloroethane.

The oxidation of chlorinated volatile organic compounds on CeO2 is hindered by its high susceptibility to chlorine poisoning, resulting in a reduced efficiency and stability. In this study, Ru- and Nb-co-modified CeO2 catalysts were designed to achieve excellent activity, stability, and CO2 selectivity in the catalytic oxidation of 1,2-dichloroethane (EDC). The formation of Nb-O-Ce bonds was observed to enhance the surface acidic sites, thereby improving HCl selectivity and reducing the production of chlorinated byproducts. Meanwhile, it inhibits the formation of Ru-O-Ce and promotes the generation of highly dispersed RuO2 particles on the surface, enhancing the redox properties and mobility of the surface oxygen, thus increasing CO2 selectivity. In situ diffuse reflectance infrared Fourier transform spectroscopy results revealed that chlorine species preferentially attach to Nb species rather than to oxygen vacancies on the Ru/Nb/CeO2 catalyst. This allows more alkane groups to oxidize to formate on the oxygen vacancies, reducing byproduct concentration. Additionally, the oxidation of alkane groups to carboxylic acids is initiated on the Nb species, completing a comprehensive oxidation process under the synergistic effect of RuO2.

Catalytic Application of Cs‐Substituted Phosphotungstic Acid (CsxH3‐xPW12O40)‐Mesoporous Zirconium Phosphate (m‐ZrP) Nanocomposite Towards Synthesis of Structurally Diverse Tetrazole Moieties

AbstractThe rational design of a high surface area heterogeneous nanocomposite catalyst with well‐defined surface acidic sites and structural porosity is a promising approach with potential application in expeditious synthesis of biologically active molecules/scaffolds. In this work, mesoporous zirconium phosphate (m‐ZrP) was synthesized through a hydrothermal process and used as a porous matrix for dispersion of cesium‐exchanged phosphotungstic acid (CsxH3‐xPW12O40) nanoparticles to prepare CsxH3‐xPW12O40‐mZrP nanocomposite systems. Various characterization techniques, including XRD, UV–vis‐DRS, FTIR, FESEM, HRTEM, TGA‐DTA, BET, and TPD, were used to understand the structural, morphological, and surface properties of the composites. XRD analysis revealed the presence of m‐ZrP and cubic CsxH3‐xPW12O40 crystalline phases in the nanocomposite materials. A microscopic study indicated the existence of rod‐shaped morphology that was formed by the coalescence of a large number of spherical nanoparticles with diameters between 150 and 200 nm. The dispersion of CsxH3‐xPW12O40 over the m‐ZrP surface results in significant enhancement of medium and strong acidic sites, with the maximum number of acidic sites observed for the Cs0.5‐PTA‐mZrP composite (0.406 mmol g−1). The catalytic activity of the CsxH3‐xPW12O40‐mZrP nanocomposites was evaluated for rapid synthesis of tetrazole derivatives through [3 + 2] cycloaddition reactions of substituted nitrile and NaN3 under mild conditions. The detailed optimization study revealed that the use of Cs0.5‐PTA‐mZrP catalyst in DMF media afforded 90% yield of the tetrazole at 120 °C. Reaction kinetics study suggested that the optimal Cs0.5‐PTA‐mZrP catalyst exhibited the highest reaction rate of 2.06 × 10−3 mmol h−1m−2 towards tetrazole formation. Structurally diverse tetrazole derivatives in high yield and purity were synthesized under mild conditions using CsxH3‐xPW12O40‐mZrP nanocomposite as catalyst.

Revealing insights into the unexpected effects of ZnO on selective catalytic reduction (SCR) activity of the CeOx-WO3 catalyst

This study delved into the intriguing impact of zinc oxide (ZnO) on the selective catalytic reduction (SCR) performance of a CeOx-WO3 catalyst with a Ce/W molar ratio of 3:2 (denoted as CW). The introduction of ZnO, at low concentrations of 1 wt% or 3 wt%, resulted in a diminution of the catalyst’s surface acid sites, which hampered the adsorption of NH3 and negated the benefits of improved NH3 activation due to the enhanced oxidative capacity. Consequently, the proceeding of the SCR reactions was significantly impeded, with a marked decrease in NOx conversion to approximately 42 % at 200 °C, which was nearly half that of the virgin CW catalyst. In contrast, increasing ZnO loading to 5 wt% facilitated the formation of ZnWO4, which introduced additional strong acid sites and bolstered NH3 adsorption at moderate and high temperatures. This, in conjunction with the heightened reactivity of surface Ce4+, resulted in a resurgence of deNOx performance, with a NOx conversion increase of ∼ 13 % at 250 °C compared to the catalyst with 3 wt% ZnO. Conversely, escalating ZnO loading to 7 wt% disrupted the formation of ZnWO4 and the excess ZnO neutralized the catalyst’s acid sites, thereby hindering NH3 adsorption and reducing NOx conversion. These insights were instrumental for the prospective application of the CeOx-WO3 catalysts under heavy metal-rich conditions.

Functionalized construction of multiple active centers for durability controlling during catalytic combustion of chlorinated aromatic hydrocarbons

The catalytic combustion of chlorine-containing VOCs primarily encounters the bottleneck of catalyst poisoning by chlorine, thereby impeding the further industrial application of this technology. The development of multi-active catalytic materials for discerning chlorine fixation, chlorine transfer, deep oxidation during elimination of chlorine-containing VOCs can mitigate catalyst chlorination and enhance stability. Herein, we utilizing LDHs as catalyst precursors and successfully synthesized flower-like Co2FexCr1-xOy catalyst with different functionalized reaction centers. The addition of Cr improved the surface lattice oxygen, oxygen vacancies, and acid sites of catalyst. The removal efficiency of CB can be achieved >90 % at 247 °C (WHSV = 33000 mL · g−1·h−1). The fixation of dissociated chlorine contributed by Cr not only enhances oxidation performance and directional adsorption of chlorine, but also improves carbon deposition resistance and catalyst sintering resistance significantly. Compared with Co2Fe1Oy, Co2Fe0.67Cr0.33Oy catalyst achieves a remarkable threefold reduction in surface carbon deposition. The DFT calculation revealed that water dissociation energy over the Co site is −0.72 eV, which is significantly lower than Fe (−0.59 eV) and Cr (−0.17 eV), facilitating water dissociation and subsequently removes a substantial amount of accumulated chlorine on Cr to form HCl. With the help of In situ DRIFT and GC/MS analysis, we found the efficient removal of chlorine atoms enhances the exposure of active sites on the catalyst surface with hydrolyzed hydroxyl group, which facilitating the conversion of aromatic hydrocarbons into a greater quantity of maleate and carboxylate species. This phenomenon is beneficial for the subsequent mineralization process of chlorobenzene. This work provide valuable insights for multi-active site catalysis mechanism in practical applications aimed at eliminating chlorinated organic waste gases from industrial emissions.

Ultrathin 2D/2D MoS2/Bi2WO6 S-scheme heterojunction for boosting photocatalytic degradation of ciprofloxacin

A series of 2D/2D MoS2/Bi2WO6 S-scheme heterojunctions consisting of ultrathin MoS2 nanosheets (MS, 1.6 nm) and ultrathin Bi2WO6 nanosheets (BWO, 1.5 nm) were developed for photocatalytic degradation of ciprofloxacin. The samples with 5 % mass ratio of MS (5 %MS/BWO) exhibits the almost complete degradation of ciprofloxacin (≈100 %) under visible light. It is evidenced that the formation of S-scheme heterojunction with close interfacial interaction facilitates the photoinduced carrier separation and the generation of surface acid sites. The activation of ciprofloxacin molecules is realized through the coordinately interaction of C-N and C=O with the surface W sites. Moreover, the OVs in BWO side is a convenient pathway for activated of O2, embodying in the generation of •O2− and •OH under visible light over photocatalyst. Such an association of charge transfer mechanism with coordination activation shows the enhanced photocatalytic performance toward ciprofloxacin. This work provides a motivation which designs an S-scheme heterojunction photocatalyst with the ability to activate the specific group in molecules to comprehend the degradation of antibiotics.

Determination of surface acidity of mixed oxide of silicon and titanium by calorimetric titration

Silica-titania mixed oxide with catalytic and adsorption properties has been of great academic and industrial interest. Metal oxides supported on silica have been used as a matrix for immobilizing electron transfer mediators, generating materials with diverse properties. The characterization of the surface acidity of these materials is essential and has been carried out using various techniques, including IR spectroscopy and calorimetry. However, no single technique completely analyses the present acidic sites. This study used calorimetric titration to investigate a mixed oxide containing titanium and silica, prepared by the sol-gel method, and its interaction with pyridine. The results showed that thermal treatment increased the enthalpy values (ΔH), indicating water removal from the matrix surface. The presence of pyridine resulted in a decrease in ΔH values, suggesting a preferential occupation of the stronger acidic sites. After thermal treatments between 473 and 573 K, the solids exhibited similar ΔH values, indicating a homogenization of the surface acidic sites. Calorimetric analysis revealed that the acidic sites were occupied in descending order of strength, with the strongest sites being filled initially. The increase in temperature did not result in new acidic sites but rather in greater occupation of the existing ones. Correlation between calorimetric and infrared data is suggested as the next investigation step. Thus, the results of this study contribute to a deeper understanding of the physicochemical properties, especially regarding their surface acidity, with the potential for more effective and controlled practical applications of this silica-titania mixed oxide in catalysis and adsorption.

Insights into Si/Al ratios for enhanced performance of β-zeolites in thermocatalytic cracking of crude oil to light olefins

The escalating demand for key petrochemicals, particularly ethylene and propylene, underscores the critical need for proficient catalysts in crude oil conversion processes. Attaining high propylene selectivity necessitates catalysts with superior adsorption capacity, thermal stability, moderate surface acidity, and pores large enough to facilitate the diffusion of larger crude oil molecules. In the present study, three different BEA Zeolites (β-zeolite) catalysts were successfully synthesized by hydrothermal method and used for catalytic cracking of Arabian Light crude oil to produce valuable petrochemical products, such as propylene, ethylene, and naphtha. The catalysts were characterized using 27Al and 29Si NMR, NH3-TPD, BET, XRD, TGA, FTIR, XRF, and FE-SEM. The thermocatalytic cracking of Arabian Light crude oil was evaluated in a fixed-bed microactivity test (MAT) unit between 550 and 600 °C. The as-prepared β-zeolite with a Si/Al ratio of 50 exhibited better catalytic activity in the catalytic cracking of Arabian Light crude oil compared to counterparts with Si/Al ratios of 35 and 65, This superiority can be attributed to its optimal combination of surface acid site distribution, textural properties, surface morphology, and high adsorption capacity. The highest feed conversion (83.4 %) and selectivity to propylene (16.11 %) were attained using β-zeolite with a Si/Al ratio of 50 at 600 °C. Importantly, our findings suggest that these catalysts hold significant potential, rivalling primary MFI catalysts like ZSM-5 commonly employed in similar reactions. This underscores their promise as catalysts of choice in the realm of catalytic cracking processes, paving the way for advancements in petrochemical production.

Surface Acidic Species-Driven Reductive Amination of Furfural with Ru/T-ZrO2.

Catalyst development for upgrading bio-based chemicals towards primary amines has increasingly attracted owing to their applications in the pharmaceutical and polymer industries. The surface acidic sites in metal oxide-based catalysts play a key role in the reductive amination of aldehydes/ketones involving H2 and NH3; however, the crucial role of the type of surface acidic species and their strength remains unclear. Herein, this study exhibits the catalytic reductive amination of furfural (FUR) to furfurylamine (FUA) with Ru supported on tetragonal (Ru/T-ZrO2) and monoclinic (Ru/M-ZrO2) ZrO2. Ru/T-ZrO2 exhibited an 11.8-fold higher rate of reductive amination than Ru/M-ZrO2, giving a quantitative yield of FUA (99 %) at 80 °C in 2.5 h and is recyclable up to four runs. Catalyst surface investigation using spectroscopic techniques, like X-ray photoelectron, electron paramagnetic resonance, and Raman, confirm higher oxygen vacancy sites (1.6 times) on the surface of Ru/T-ZrO2 compared to Ru/M-ZrO2. Moreover, in-situ NH3-diffuse reflectance infrared Fourier transform spectroscopy studies display that Ru/T-ZrO2 has more moderate Bronsted acidic sites (surface H-bonded hydroxyl groups) than Ru/M-ZrO2. Further, the controlled experiments and poisoning studies with KSCN and 2,6-lutidine suggest the crucial role of Ov sites (Lewis acidic sites) and surface hydroxyl groups (Bronsted acidic sites) for selective FUA formation.

Challenging design of highly active Pt/CeO2–TiO2/ZSM-5 catalysts for VOCs low-temperature removal

Four Pt/CeO2–TiO2/ZSM-5 catalysts with different Pt species dispersion states and acidic properties were designed, and key factors affecting the oxidation activity of various VOCs (benzene, DCE, ethyl acetate and acetonitrile as typical organic compounds of aromatic hydrocarbon and halogen/oxygen/nitrogen-containing VOCs, respectively) were identified in the present work. The strength of the acid and oxidation sites on the surface of catalysts and their synergistic interaction play a crucial role. Highly dispersed Pt species and its strong redox ability promote low-temperature oxidation of benzene. A synergistic interaction between the acid and oxidation sites is required to achieve high DCE oxidation activity. An abundance of surface acid sites (particularly strong acid sites) favors the adsorption and dechlorination to form vinyl chloride of DCE, and the strong redox ability of oxidation sites would accelerate the deep oxidation of intermediates (such as vinyl chloride and acetic acid, etc.). For ethyl acetate or acetonitrile oxidation, the strong acidic property of the catalyst plays a prior role for their catalytic oxidation, which facilitates the low-temperature hydrolysis of ethyl acetate or acetonitrile. This work provides a significant thought to design and synthesize high activity catalysts for low-temperature oxidation of various VOCs pollutants.

The effect of SO2 on NH3-SCR reaction synergistic CO oxidation over a Mn-Co-Ti catalyst

Mn–Co–TiO2 prepared using an impregnation method was applied to synergistic NH3-based selective catalytic reduction (NH3-SCR) and CO oxidation in a simulated flue gas. The NO conversion, NO oxidation, and CO oxidation were substantially enhanced after adding 15% Co3O4 to the 20MnTi catalyst. In an NO or NO + NH3 atmosphere, CO oxidation over the Mn–Co–TiO2 catalyst was mainly restrained by the competitive adsorption and formation of sulfate species. In contrast, the NH3-SCR reaction progressed almost unimpeded in a CO atmosphere. A SO2 atmosphere drastically reduced the NO conversion of the catalyst at lower temperatures and almost completely suppressed the oxidation activities toward NO and CO. The amount of remaining NO oxidation (approximately 10%) was primarily contributed by gas-phase oxidation of NO by O2. Next, fresh and SO2-poisoned Mn–Co–TiO2 were characterized using various methods. Results indicated that no conspicuous change occurred in the crystal structure of the samples after SO2 poisoning, but numerous sulfate products were deposited on the catalyst surface. The deposition of sulfate-species byproducts decreased the specific surface area and pore volume of the catalyst and shifted the surface acid sites to a higher temperature range, further reducing the CO oxidation performance. Moreover, the catalytic reaction of CO and NO followed the Eley–Rideal mechanism. Furthermore, the mechanisms through which multicomponent flue gases influence the synergistic NH3-SCR and CO oxidation performance were proposed.

Effects of MOx modification (M = Mn, Ce, and Fe) on the SCR catalytic properties of the CrOx-WOx mixed oxide catalysts

In this study, a series of MOx-modified (M = Mn, Fe, and Ce) CrOx-WOx mixed oxides were synthesized via the sol-gel technique for the selective catalytic reduction of NOx with NH3. Given the addition of MnOx or CeOx, the availability of the catalyst surface acid sites tended to decline, which negatively affected the proceeding of the deNOx process. Moreover, the retention of oxidative ability by introducing MnOx also favored the over-oxidation of NH3, which accelerated the additional formation of NOx and created a crucial barrier for the increment in the higher-temperature deNOx activity. Apparently, <80 % of the NOx could be effectively eliminated from the working gas within the whole temperature range for the CrCeW and CrMnW samples. By contrast, doping FeOx was able to introduce ample acid sites onto the catalyst surfaces, which was beneficial for the adsorption of NH3 and subsequently the facilitation of the progression of the deNOx process. Furthermore, the weakened oxidizability suppressed the over-oxidation of NH3. Consequently, a broad operating temperature window was obtained for the FeOx-doped catalyst; >90 % NOx conversion efficiency was achieved in the temperature range of 230–450 °C. During the deNOx process, the Eley-Rideal mechanism dominated over the four investigated samples.

Significant Promotional Effect of Nb Doping in Bifunctional Pd/WOx Nanocatalysts on One‐Step Benzene Hydroalkylation

AbstractThe development of high‐efficiency heterogeneous bifunctional metal‐acid catalysts with an appropriate metal‐acid balance for the production of cyclohexylbenzene (CHB) via the one‐step tandem benzene hydroalkylation still faces a dilemma because of the difficulty in inhibiting the over hydrogenation of benzene substrate and cyclohexene intermediate and controlling target product selectivity. In this study, Nb‐doped WOx supported Pd nanocatalysts were developed. It has been shown that doping Nb into WOx supports altered surface properties and microstructures of catalysts, resulting in the generation of more surface acidic sites and defective W−Ov−Nb structures (Ov: oxygen vacancies). As‐constructed Pd‐based nanocatalyst with only 0.1 wt % Pd loading and a Nb/(Nb+W) molar ratio of 0.25 exhibited superior catalytic benzene hydroalkylation performance to undoped supported Pd catalyst, with a much higher yield of CHB (35.6 %) at 220 °C. It was authenticated that highly dispersed Pd sites facilitated the dissociation of hydrogen molecules, defective W−Ov−Nb structures were conductive to the surface transfer of active hydrogen species, a large number of acidic sites favored benzene/cyclohexene intermediate adsorption, and abundant Brønsted acidic sites promoted the alkylation between cyclohexene intermediate formed and benzene. Accordingly, excellent cooperative catalysis between Pd sites, acidic sites, and oxygen vacancies contributed to improved catalytic performance of Nb‐doped WOx supported Pd catalysts in benzene hydroalkylation. This research presents an alternative for the creation of low‐cost practical bifunctional metal‐acid catalysts for highly efficient benzene hydroalkylation.

Synthesis and characterization of aluminosilicate and zinc silicate from sugarcane bagasse fly ash for adsorption of aflatoxin B1

Sugarcane bagasse fly ash, a residual product resulting from the incineration of biomass to generate power and steam, is rich in SiO2. Sodium silicate is a fundamental material for synthesizing highly porous silica-based adsorbents to serve circular practices. Aflatoxin B1 (AFB1), a significant contaminant in animal feeds, necessitates the integration of adsorbents, crucial for reducing aflatoxin concentrations during the digestive process of animals. This research aimed to synthesize aluminosilicate and zinc silicate derived from sodium silicate based on sugarcane bagasse fly ash, each characterized by a varied molar ratio of aluminum (Al) to silicon (Si) and zinc (Zn) to silicon (Si), respectively. The primary focus of this study was to evaluate their respective capacities for adsorbing AFB1. It was revealed that aluminosilicate exhibited notably superior AFB1 adsorption capabilities compared to zinc silicate and silica. Furthermore, the adsorption efficacy increased with higher molar ratios of Al:Si for aluminosilicate and Zn:Si for zinc silicate. The N2 confirmed AFB1 adsorption within the pores of the adsorbent. In particular, the aluminosilicate variant with a molar ratio of 0.08 (Al:Si) showcased the most substantial AFB1 adsorption capacity, registering at 88.25% after an in vitro intestinal phase. The adsorption ability is directly correlated with the presence of surface acidic sites and negatively charged surfaces. Notably, the kinetics of the adsorption process were best elucidated through the application of the pseudo-second-order model, effectively describing the behavior of both aluminosilicate and zinc silicate in adsorbing AFB1.