Ce Species Research Articles

Synergetic catalysis of Ni@C@CeO2 for driving ab/desorption of MgH2 at moderate temperature

Multiple catalysts have exhibited high activity on improving the hydrogen storage performance of MgH2. Herein, the hydrogen ab/desorption kinetics of MgH2 is significantly improved by using Ni@C@CeO2 as the catalyst. The results show that 10 wt%-Ni@C@CeO2 doped MgH2 can absorb 4.51 wt% hydrogen within 60 min under low temperature 75 °C. Furthermore, the MgH2-Ni@C@CeO2 composites release approximately 4.88 wt% H2 within 10 min at 325 °C. Moreover, the composites show excellent cycling performance, with negligible decrease in hydrogen storage capacity, hydrogen uptake rate and hydrogen release rate after ten cycles at 350 °C. The Rietveld refinement of X-ray diffraction and transmittance electron microscopy measurements reveal that Mg2NiH4/Mg2Ni and CeH2.73 phases are in-situ formed. The mutual conversion of “Mg2Ni/Mg2NiH4” during hydrogen ab/desorption is a well-known “hydrogen pump” effect, which improvs the hydrogen storage performance of MgH2. The presence of CeH2.73 accelerate the conversion of Mg2Ni/Mg2NiH4, which we call ‘facilitated hydrogen pump’ effect. This attempt paves a potential way to achieve high performance Mg-based composites hydrogen storage materials via collaborative action between Ni and Ce species.

CoCe composite catalyst for the CH4/CO2 reforming reaction: Synergistic effects between Co and Ce species

The greenhouse gases CH4 and CO2 can be use as feedstock to prepare syngas (CO + H2) by CH4/CO2 reforming reaction, and the syngas can be used to produce high value-added chemicals through Fischer-Tropsch reaction. That is, the CH4/CO2 reforming reaction can provide an effective way to rationally use CO2 and CH4. The CoCe catalysts were prepared by impregnation method and grinding method, respectively, and the physicochemical properties were characterized by H2-TPR, XRD, BET, Quasi in-situ XPS and CO2-TPD. The synergistic effects between Co and Ce species can promote the CH4 and CO2 molecules to be continuously and rapidly activated, so that the CoCe catalysts exhibited good catalytic activity for the CH4/CO2 reforming reaction. The preparation methods can affect the dispersion of the Co species and the thermal stability of the oxygen vacancies on the CoCe catalysts to affect catalytic activity. The impregnation method is conducive to the Co species dissolving into the CeO2 lattice to form oxygen vacancies with high thermal stability, and the Co species on the CeO2 surface were in a highly dispersed state, which can provide more stable catalytic activity centers. Thus, the catalysts prepared by impregnation method displayed superior catalytic performances for CH4/CO2 reforming reaction. And the CH4 and CO2 conversions can reach 43.4% and 29.0% at the reaction temperature of 600 °C, respectively.

Oxidative Desorption of Adsorbed Sulfur on Platinum Surfaces Modified with Cerium Species

In polymer electrolyte membrane fuel cells, hydrogen oxidation and oxygen reduction reaction occur at platinum (Pt) catalyst surface. Pollutants in air and hydrogen fuel, especially, sulfur (S) species, often strongly adsorb on the Pt surface, resulting in reduced electrochemically active surface area, namely poisoning effect. Because such poisoning causes the significant deterioration of cell performance and durability, understanding and control of adsorption behavior of S species are very important. Thus, it is necessary to develop a new method or material for recovery from S poisoning in anode.In this study, a Pt(111) single crystal electrode was modified with a Ce species and its electrochemical property was compared with a bare Pt electrode. The modification with Ce species was accomplished by immersion in a Ce (NO3)3 + HClO4 aqueous solution with bubbling Ar + H2 gas through the solution for 1 h or applying the potential at -0.2 V in a Ce (NO3)3 + HClO4 aqueous solution. The modification of Pt(111) electrode with Ce species drastically changed the electrochemical responses; hydrogen adsorption/desorption waves become smaller and adsorption/desorption waves of hydroxy group disappeared because of the presence of adsorbed Ce species. Adsorbed species was identified as a Ce3+ ion by XANES spectrum.After the bare Pt(111) electrode was immersed in an aqueous solution containing sodium sulfide, three types of adsorbed S species, HS and S/Sn were detected by XPS. HS was reductively desorbed from Pt electrode surface at potential cycling between 0.0 and 0.2 V vs. RHE (-0.2 and 0.0 V vs. Ag/AgCl). S/Sn species remained during this potential cycling but oxidatively desorbed when the positive limit of potential cycling was 0.6 V vs. RHE (0.8 V vs. Ag/AgCl). The hydrogen adsorption/desorption current gradually increased as repeating potential cycling between 0.0 and 1.0 V vs. RHE (-0.2 V and 0.8 V vs. Ag/AgCl).After the Ce-modified Pt(111) electrode was immersed in an aqueous solution containing sodium sulfide, an anodic current assignable to the oxidative desorption of S species appeared at 0.3 V. The peak current decreased as repeating potential cycling between 0.0 and 0.7 V vs. RHE (-0.2 V and 0.5 V vs. Ag/AgCl). After this potential cycling, the peak area of S2p region of XPS spectra decreased as well as Ce 3d peak. The oxidative desorption of S and Sn on the Ce-modified Pt(111) electrode took place at 0.5 V vs RHE (0.3 V vs. Ag/AgCl) which is much more negative than that of bare Pt(111) electrode (1.0 V vs. RHE (0.8 V vs. Ag/AgCl)). Thus, modification of Pt(111) electrode with Ce species promoted the oxidative desorption of S species.

Effect of the surface composition of MnOX-CeOX 3D-printed monolithic catalysts toward total oxidation of toluene.

Successful fabrication of Mn-based 3D-printed monoliths by stereolithography (SLA) is reported for the first-time in this work. The catalytic performances, as function of the surface composition, of the developed monoliths were evaluated by the total oxidation of toluene. The monolith with a surface composition of Mn0.7Ce0.3 showed the highest catalytic efficiency (98%) with a T90 value of 322 °C and acceptable catalytic stability after a second reaction cycle. By changing space velocity values, the T90 value can decrease to 311 °C. Microstructural and surface characterizations confirm the formation of Mn2O3 and Ce species on Mn sites and the homogeneous dispersion of Mn and Ce species on the surface of the 3D-printed monoliths. For comparison purposes, a single MnOX and CeOX monoliths were also synthesized and tested by toluene total oxidation, which confirms the cooperative effect between the oxygen storage capacity of Ce and the redox ability of Mn species observed in Mn0.7Ce0.3 monolith catalyst, giving rise to the highest catalytic activity. These results pointed out the promising catalytic properties of the developed Mn-based 3D-printed monolith catalysts for the total oxidation of volatile organic compounds at a low cost, which is an interesting alternative to mitigating atmospheric emissions.

Enhanced low-temperature performance of Al-rich Cu-SSZ-13 by Ce modification upon hydrothermal aging for NH3-SCR

3wt.% Cu/SSZ-13 (Cu3/Z) and Ce modified 3wt.% Cu/SSZ-13 (Ce-Cu3/Z) catalysts were prepared and then hydrothermally aged. The Ce-modified Ce-Cu3/Z catalyst revealed excellent NH3-SCR activity and hydrothermal stability. Combined with a series of characterizations, it was proved that the introduction of Ce could inhibit the dealumination, and prevent the aggregation of Cu ions to form CuOx and CuAl2O4 species upon hydrothermal aging, thus improving the hydrothermal stability of Ce-Cu3/Z. In addition, Ce could interact with Cu species to enhance the reducibility of catalyst, and the interaction between Ce and Cu species was strengthened after hydrothermal aging. Also, the presence of Ce species could enhance the NH3 and NOx adsorption capacity of the catalyst, resulting in higher NH3-SCR activity of Ce-Cu3/Z after hydrothermaly aged at 700 °C. In situ DRIFTS results showed that the NH3-SCR reaction followed both E-R and L-H mechanisms on the Cu3/Z-700 and Ce-Cu3/Z-700 catalysts at 150 °C. Ce doping could promote the formation of L-NH3 (NH3 species coordinated to Lewis acid sites) and nitrate species on the Ce-Cu3/Z-700 catalyst, as well as the involvement of L-NH3 in the reaction, which play a crucial role as the main active intermediates at low temperature.

Promoting the catalytic activity and SO2 resistance of CeO2 by Ti-doping for low-temperature NH3-SCR: Increasing surface activity and constructing Ce3+ sites

CeO2-based oxides are promising catalysts for low-temperature selective catalytic reduction of NOx with NH3 (NH3-SCR), but the poor SO2 poisoning resistance hampers its further application. Herein, we developed a Ti-doped CeO2 (Ti-CeO2) catalyst with high specific surface area by calcining TiSO4-doped Ce-MOF precursor for NO removal. On Ti-CeO2, abundant Ti3+ sites are generated by the thermally reducing carbon in the organic ligand during calcination, the electronic interaction between Ti3+ and Ce4+ leads to the generation of many more exposed Ce3+ sites, effectively preventing the sulphuration of surface Ce species to Ce2(SO4)3. Besides, the residual sulfate species provides plentiful Brønsted acid sites for NH3 adsorption. Therefore, both the catalytic performance and SO2 resistance of CeO2 are significantly enhanced after Ti-doping. Remarkably, above 80% NO conversion is obtained between 220 and 450 °C on Ti0.10-CeO2 (the molar ratio of Ti:Ce is 0.10 in the synthesis process), and the NO conversion maintains around 76.0% for 170 h in the presence of 100 ppm SO2 and 5 vol% H2O at 250 °C. The reaction on CeO2 and Ti-CeO2 follow the Langmuir-Hinshelwood (L-H) mechanism, but abundant Ce4+ in CeO2 having high oxidation ability leads to the generation of plentiful stable nitrate or nitrite to occupy the active sites. In contrast, the over oxidation of NO and SO2 adsorption are inhibited because of Ti-doping, resulting in superior catalytic performance in the SCR reaction.

Simultaneous Generation of Ammonia during Nitrile Waste Gas Purification over a Silver Single-Atom-Doped Ceria Catalyst.

Catalytic elimination of toxic nitrile waste gas is of great significance for preserving the atmospheric environment, but achieving resource utilization during its destruction has been less explored. Herein, this study proposed a universal strategy for nitrile waste gas purification and NH3 generation simultaneously. The developed silver single-atom-doped ceria nanorod (Ag1/R-CeO2) was endowed with near complete mineralization and around 90% NH3 yield at 300-350 °C for the catalytic oxidation of both acetonitrile and acrylonitrile. The introduction of the Ag single atom created more surface oxygen vacancies, thereby promoting water activation to form abundant surface hydroxyl groups. As a benefit from this, the hydrolysis reaction of nitrile to generate NH3 was accelerated. Meanwhile, the electron transfer effect from the Ag atom to Ce and hydroxyl species facilitated NH3 desorption, which inhibited the oxidation of NH3. Moreover, the increased surface oxygen vacancies also promoted the mineralization of hydrolysis carbonaceous intermediates to CO2. In contrast, the Ag nanoparticle-modified sample possessed stronger reducibility and NH3 adsorption, leading to the excessive oxidation of NH3 to N2 and NOx. This work provided a useful guidance for resourceful purification of nitrile waste gas.

In-situ formation of carbon-doped cerium-zirconium solid solution as a superacid catalyst for the removal of NOx

Defects engineering in nanomaterials can be used to precisely and effectively modulate catalysts’ reactivity. Here we report a highly efficient NH3-SCR catalyst constructed with in-situ formation of carbon-doped CeZrO2−x with dual defects, in which O atoms are substituted by C atoms to generate surface oxygen vacancies and subsurface oxygen substitutions. The carbon-doped CeZrO2−x exhibit superior activity and better SO2/H2O resistance compared with traditional bulk CeZrOx and V2O5-WO3/TiO2. The related characterization results reveal that the surface oxygen vacancy and subsurface oxygen substitution resulted in the formation of a large number of unsaturated coordination Ce and Zr species on catalyst’s surface, which contributed to the adsorption and activation of NH3, thus promoting the catalytic activity. Meanwhile, the abundant oxygen vacancy also stimulated the E-R reaction pathway over carbon-doped CeZrO2−x. In addition, it was proved that more zirconium sulfate and unstable ammonium sulfate species were exposed over carbon-doped CeZrO2−x, benifiting the better SO2-tolerance.

Revealing the effect of electronic interaction between dual redox sites on CeO2-Fe2O3 NH3-SCR catalyst through interface contact tailoring

Due to the requirements of different applications environments, higher catalytic activity or SO2 and H2O tolerance, the binary or ternary metal oxide NH3-SCR catalysts with dual redox sites have been widely studied in recent years. The electronic interaction between the dual redox sites has a significant impact on the catalyst performance. Herein, a series of CeO2-Fe2O3 composite catalysts with continuously enhanced interface contact as well as electronic interactions were prepared through a facile grinding method. The activity tests showed that neither the catalyst with the least interfacial contacts nor the one with the greatest interfacial contacts exhibited the highest NOx removal activity. The comprehensive characterizations demonstrated that the apparent physicochemical properties including the NH3 adsorption ability, redox property, and so on, changed in favor of NH3-SCR reaction when enhancing the interface contact for the CeO2-Fe2O3 composite catalysts. However, the reaction mechanism as well as the reactivity of main NH3 and NO adsorbed species were also altered by the electronic interactions between Ce and Fe active species. The unsatisfactory NOx removal activity of the CeO2-Fe2O3 catalyst with strongest electronic interactions between Ce and Fe active species was explained by the reactivity of main NH3 and NO adsorbed species. This work can provide new ideas for improving the performance of NH3-SCR catalysts through changing the interface contact and electronic interaction between the dual redox sites.

An effective strategy to enhance the sulfur resistance of Ce-based catalyst for low temperature SCR reaction

SO2 has a significant impact on SCR reaction, and how to suppress the effect of SO2 on Ce-based catalyst activity has been a goal pursued by the scientific community. In this work, the CeSmFTi catalyst was prepared by one-pot hydrothermal method to study the catalytic activity and SO2 resistance performance in NH3-SCR reaction. The experimental findings suggested that Ce5Sm1FTi94 catalyst had better catalytic performance, with the NO conversion exceeding 90% at 320 °C. After enduring SO2 test, the NO conversion could gradually recover to more than 80%. The results showed that the presence of CeF3 efficiently regulated the proportion of active state Ce3+ and accelerated the “fast SCR” reaction, which significantly enhanced the catalytic performance of the catalyst and inhibited the oxidation of SO2. Notably, doping a certain amount of Sm into Ce5FTi94 catalyst not only improved the surface acidity and redox performance, but also promoted the electron transfer and interaction between Ce and Sm species, thereby inhibiting the combination of SO2 and cerium species. Therefore, the formation of sulfate species on the catalyst was minimized, resulting in a better SO2 tolerance. Simultaneously, the in-situ DRIFTs analysis revealed that both L-H and E-R mechanisms were presented on Ce5Sm1FTi94 catalyst to carry out the NH3-SCR reaction process, with the L-H mechanism being dominant.

Functional distinction of different components in SmCeMn/Ti catalytic system for NH3-SCR

Active components play different roles in improving catalytic performance due to their different physicochemical properties. In multicomponent catalysts, different components provide the possibility of multiple structures and catalytic feasibility, but the role played by specific components in improving performance becomes confusing. This work synthesized a series of SmCeMn/Ti catalysts with different metal components exposed on the outer surface to study their catalytic roles for NH3-SCR. For the contribution of different components to the catalytic activity, Mn contributes more B-acid sites and Mn4+, facilitating NO conversion. Ce generates a large amount of Mn4+ through a strong redox reaction with Mn3+ and generates abundant oxygen vacancies during the reaction process due to its strong oxygen storage-release capacity, and Sm acts as a sacrifice site for electron transfer with Mn to improve the sulfur resistance. Further investigations show that the three components have different adsorption behaviors for reactant gas and thus provide various catalytic feasibility. This work establishes a specific catalytic model for Sm, Ce, and Mn species, respectively, which provides experimental guidance to improve activity and sulfur resistance by active component control.

Investigation of Ce/BEA as a passive NOx adsorber: 1. The occurrences of cerium and adsorption behavior

Ce/BEA has great potential as a passive NOx absorber (PNA) to reduce the NOx emissions during the cold start phase especially in diesel engine for its high resistance to CO and suitable NOx desorption temperature range. However, as a novel material, its physical and chemical properties still remain unknown. In this work, Ce/BEA was synthesized by ion-exchange method to identify the active species in NOx adsorption, compared with aggregated Ce species in Ce/SiAlOx prepared by impregnation method. X-ray diffraction (XRD), high resolution-transmission electron microscopy (HR-TEM) and aberration-corrected-scanning transmission electron microscopy (AC-STEM) were performed to confirm the isolated single atom formation of Ce species in Ce/BEA. UV-vis diffraction reflection spectra (DRS) and X-ray photoelectron spectroscopy (XPS) were conducted to find the difference of chemical environment between the isolated Ce species and aggregated ones. PNA performance evaluation and temperature programmed reduction of hydrogen (H2-TPR) results show the high NOx storage capacity and active oxygen species quantity in Ce/BEA. It is also found that the main NOx adsorption species are Ce4+–O∗ rather than Ce3+. NOx-diffuse reflectance infrared Fourier transform spectroscopy (NOx-DRIFTS) confirms that the bidentate nitrite species are the critical NOx adsorption intermediates and the conception of NOx adsorption and desorption processes is proposed.

Critical role of Photo-electrode with Ce-g-C3N4 in multi-stage microbial fuel cells cascade reactor treating diluted hyper-saline industrial wastewater rich in amines

Treatment of chemical industrial wastewater often faces problems of large volume occupation, high cost, and long processing time. In this study, low-content Ce-modified g-C3N4 was prepared and used as a catalyst on stainless steel mesh photo-cathode in constructing a multi-stage cascade microbial fuel cell system to reduce treatment costs in an energy-saving way. The large specific surface area (332.5 m2 g−1) and mesoporous structure of the material, is favorable for catalytic reactions, in which Ce elements were mainly present in single atoms. The characterized catalyst indicated a pronounced effect of Ce species in increasing photo-current and the synergistic pollutant removal, microbial bio-degradation and cascade operation stability. In Batch-mode (light illumination, aeration, total HRT (hydraulic residence time) of 54 h) treatment through three cascade reactors, removed 88% COD (Chemical Oxygen Demand). With 0.5 mM PMS (peroxymonosulfate), 94% COD and 86% NH4+-N of the system were removed. The cascade net average COD removal capacity reached 16.04 kg per kg catalyst per day. The addition of PMS also enhanced the electricity generation. In continuous-mode, in totally 18 h treatment through the three-stages cascade reactors without PMS, overall, 83% COD and 78% TOC (Total Organic Carbon) were removed, reaching a net calculated system average COD removal capacity of 19.29 kg per kg catalyst per day. With Ce-g-C3N4 catalyst, the batch or continuous multi-stage cascade system demonstrated great technical flexibility and economic potential in treating high-strength, high-salinity amine-rich industrial wastewater.

One-pot solvothermal assembly of CeO2/Ce-BiOBr hollow microsphere heterojunctions for efficient degradation of Congo red driven by visible LED light irradiation

Morphology control and heterostructure construction are two essential aspects in designing and synthesizing photocatalysts. Herein, hollow microsphere heterojunctions of CeO2 and Ce3+ doped BiOBr (Ce-BiOBr) were fabricated adopting a facile one-pot solvothermal approach. Owing to the positively charged Ce species, the interlamellar repulsion can be reduced and the specific surface area of these microsphere can be increased. The as-generated Ce4+/Ce3+ redox centers can synergistically improve the transfer and separation efficiency of photogenerated carriers. When used to treat Congo red (CR), 0.1CBOB with a Ce/Bi molar ratio of 0.1:1 exhibits the best photodegradation efficiency (94.63%) and kinetic rate (0.01119 min−1) under visible light-emitting diode (LED) light irradiation, which are remarkably superior to pure BiOBr and CeO2. The results of radical capture experiment show that photogenerated hole (h+), superoxide radical (·O2−) are the main active species in the process of photocatalytic degradation.

Investigation of Ce/BEA as a passive NOx adsorber: 2. Hydrothermal aging deactivation mechanism

Ce/BEA has the potential to be applied as a novel passive NOx absorber (PNA) in the after-treatment of vehicles due to its considerable NOx storage capacity. However, as a vehicle exhaust after-treatment material, it must withstand the test of long-term hydrothermal aging. This work examined the deactivation mechanism of Ce/BEA during hydrothermal aging. 3.0 wt% Ce/BEA was prepared using the ion-exchange method, and then subjected to hydrothermal treatment at 650 °C with 10% H2O for 1–12 h to obtain samples with different aging extent. For comparison, the H-BEA support was aged under the same conditions. Brunauer-Emmett-Teller (BET) method, X-ray diffraction (XRD), NH3 temperature programmed reduction (NH3-TPD), 27Al MAS nuclear magnetic resonance (27Al MAS NMR), H2 temperature programmed reduction (H2-TPR), and high resolution-transmission electron microscopy (HR-TEM) were performed to characterize the changes in PNA performance, structure, Ce species, and acidity. The HR-TEM and H2-TPR results show that CeOx particles appear after hydrothermal aging, which results from the detachment and aggregation of active Ce species. Based on the 27Al MAS NMR results, we conclude that BEA zeolite dealumination leads to the loss of acidic sites and the transformation of active Ce species on the acidic sites into the less active CeOx. This is the primary reason for the hydrothermal aging deactivation of Ce/BEA.

New insights into the relationship between Cu–Ce interaction and reactive Cu species in CuOx-CeO2 catalysts for preferential oxidation of carbon monoxide in excess hydrogen

A group of CuOx-CeO2 catalysts for preferential oxidation of carbon monoxide (CO-PROX) is designed by constructing different distribution status of Cu species on similar CeO2 support to adjust the Cu–Ce interaction strength. Cycled temperature programmed reduction by hydrogen (H2-TPR) indicates the strength of Cu–Ce interaction can impact the amount and redox properties of surface highly dispersed CuOx and strongly bonded Cu-[Ox]-Ce species, which respectively determines the catalytic performance at low and high temperature. Temperature programed desorption of H2 (H2-TPD) reveals the presence of large amounts of Cu-[Ox]-Ce species can inhibit H2 adsorption and dissociation, which increases the O2 selectivity toward CO oxidation. Moreover, temperature programmed desorption of CO2 (CO2-TPD) and in situ diffuse reflectance infrared Fourier transform spectra (DRIFTs) illustrates that H2O and CO2 influences the low-temperature catalytic performance mainly by competitive adsorption with CO on surface highly dispersed reactive Cu+ sites. This work aims to shed light on the underlying Cu–Ce interaction regime, and guide the design of high-performance CuO–CeO2 catalysts in realistic reaction conditions.

Three-dimensional porous CuO-modified CeO2-Al2O3 catalysts with chlorine resistance for simultaneous catalytic oxidation of chlorobenzene and mercury: Cu-Ce interaction and structure

Chlorine poisoning effects are still challenging to develop efficient catalysts for applications in chlorobenzene (CB) and mercury (Hg0) oxidation. Herein, three-dimensional porous CuO-modified CeO2-Al2O3 catalysts with macroporous framework and mesoporous walls prepared via a dual template method were employed to study simultaneous oxidation of CB and Hg0. CuO-modified CeO2-Al2O3 catalysts with three-dimensional porous structure exhibited outstanding activity and stability for simultaneous catalytic oxidation of CB and Hg0. The results demonstrated that the addition of CuO into CeO2-Al2O3 can simultaneously enhance the acid sites and redox properties through the electronic inductive effect between CuO and CeO2 (Cu2++Ce3+↔Cu++Ce4+). Importantly, the synergistic effect between Cu and Ce species can induce abundant oxygen vacancies formation, produce more reactive oxygen species and facilitate oxygen migration, which is beneficial for the deep oxidation of chlorinated intermediates. Moreover, macroporous framework and mesoporous nanostructure dramatically improved the specific surface area for enhancing the contact efficiency between reactants and active sites, leading to a remarkable decrease of byproducts deposition. CB and Hg0 had function of mutual promotion in this reaction system. In tune with the experimental results, the possible mechanistic pathways for simultaneous catalytic oxidation of CB and Hg0 were proposed.

Synthesis of Ce‐Doped MIL‐125‐NH2 for Promoting Catalytic H2O2 Production from Water and O2 under Visible Light Irradiation

AbstractDespite the direct utilizing metal‐organic frameworks (MOFs) as promising photocatalysts for H2O2 production, their activity and selectivity are still undesirable owing to the insufficient active centers, weak visible‐light absorption, and limited charge transfer. Herein, the Ce‐doped Ti‐based MOFs MIL‐125‐NH2 photocatalysts (Ce/TiMOFs) were synthesized by a facile impregnation‐coordination method, during which the doped Ce species could not only extend the visible‐light absorption edge but also provide new reactive sites for promoting the charge transfer and selectivity of two‐electron O2 reduction. Interestingly, the optimal Ce/TiMOFs‐0.010 achieved a rate of H2O2 yield of 2464 μM h−1 g−1 with ∼3.4‐fold improvement compared to TiMOFs, attributed to the faster conversion rate of the main reactive oxygen intermediates (⋅O2−) and improved average transfer electron number. This work provides an effective strategy to optimize the photocatalytic performances of MOFs and expands the application of MOFs in the sustainable energy production field.

Effects of the Inclusion of Ce and Ni Species on Ti for Modification of K10-Clay by Sol-Gel and their Use as Catalysts in the Liquid-Phase Esterification Systems

AbstractThe modification of montmorillonite with metallic species affects directly its crystalline structure, texture, porosity, and surface. The interaction of the metallic molecules with the clay matrix, derived from the modification pathway and the characteristics of the adsorbate, modifies the physicochemical properties of montmorillonite, enabling the creation of materials with varied characteristics to be used both as catalysts and adsorbents. Small amounts of metallic species can confer various structural and physicochemical characteristics on the same montmorillonite matrix, depending on the metal incorporated. The objective of the present study was to create an acid-base catalyst based on montmorillonite K10 (K10 Mnt), modified with Ti, Ce, and Ni, for the catalytic esterification of acetic acid and penta-1-ol. K10-Mnt was modified using particles of Ti and of Ti modified with Ce and Ni. The effect of the inclusion of Ti and modified Ti species on the transformation of the physicochemical properties of the K10 Mnt and their contributions to the catalytic esterification syntheses were investigated. Samples were characterized by scanning electron microscopy coupled to an energy-dispersive X-ray spectroscopy system (SEM-EDS), powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), physisorption of N2 at 77 K (BET and BJH), and thermogravimetric analysis (TGA-DTGA). Finally, the original and modified K10 Mnt samples were tested for their catalytic esterification of acetic acid and penta-1-ol in the liquid phase.

One-pot synthesis of bimetallic CeCu-SAPO-34 for high-efficiency selective catalytic reduction of nitrogen oxides with NH3 at low temperature

NH3 selective catalytic reduction (SCR) has been widely recognized as a promising technique for reducing nitrogen oxides from diesel vehicle exhausts. High-efficiency SCR catalysts that could perform at low temperatures are essential to denitration. In this work, a series of bimetallic CeCu-SAPO-34 molecular sieves were synthesized by one-step hydrothermal method. The CeCu-SAPO-34 maintained good crystallinity and a regular hexahedron appearance of Cu-SAPO-34 after introducing Ce species, while exhibiting a higher specific surface area and pore volume. The as-prepared CeCu-SAPO-34 with 0.02% (mass) Ce constituent exhibited the best catalytic activity below 300 oC and a maximum NOx conversion of 99% was attained; the NOx removal rates of more than 68% and 94% were achieved at 150 °C and 200 °C, respectively. And the introduction of cerium species in Cu-SAPO-34 improves the low-temperature hydrothermal stability of the catalyst towards NH3-SCR reaction. Additionally, the introduced Ce species could enhance the formation of abundant weak Brønsted acid centers and promote the synergistic effect between CuO grains and isolated Cu2+ to enhance the redox cycle, which benefit the NH3-SCR reaction. This work provides a facile synthesis method of high-efficiency SCR denitration catalysts towards diesel vehicles exhaust treatment under low temperature.