Synergically regulated silver species and surface oxygen on manganese oxide for promoted activity of formaldehyde oxidation

Formaldehyde(HCHO)is a common indoor pollutant that is detrimental to human health.Its efficient removal has become an urgent demand to reduce the public health risk.In this work,Ag-MnO_(x)-based catalysts were prepared and activated under different atmosphere(i.e.,air,hydrogen(H_(2))and carbon monoxide(CO))for efficient oxidation of HCHO.The catalyst activated with CO(Ag/Mn-CO)displayed the highest activity among the tested samples with 90% conversion at 100℃ under a gas space velocity of 75,000 mL/(g_(cat)·hr).Complementary characterizations demonstrate that CO reduction treatment resulted in synergically regulated content of surface oxygen on support to adsorb/activate HCHO and size of Ag particle to dissociate oxygen to oxidize the adsorbed HCHO.In contrast,other catalysts lack for either abundant surface oxygen species or metallic silver with the appropriate particle size,so that the integrate activity is limited by one specific reaction step.This study contributes to elucidating the mechanisms regulating the oxidation activity of Ag-based catalysts.

Tuning SMSI to stabilize metallic Pd species:A case study on Pd/TiO_(2) for HCHO oxidation

Pretreatment of the carrier for supported catalysts can effectively improve the strong metal-support interaction(SMSI)and increase the dispersion of precious metals,which are critical to many important catalytic reactions.In this work,we tuned SMSI on Pd/TiO_(2)catalysts through inducing surface defects of TiO_(2)by pretreated with different atmospheres(H_(2)/N_(2),N_(2),O_(2)/N_(2))at the high temperature(800℃).Multiple characterization results illustrated that surface defects anchored Pd species and thus enhanced their dispersion.During reduction,Ti^(3+)species formed and transferred onto the metallic Pd species and then induced SMSI,which effectively stabilize Pd species in the metallic state.The stronger MSI,the more stability of Pd species.As a case,Pd/TiO_(2)–800H_(2),with strongest MSI,displayed the best HCHO oxidation performance at low temperature(10℃).

Structural basis of negative regulation of CRISPR-Cas7-11 by TPR-CHAT

CRISPR‒Cas7-11 is a Type Ⅲ-E CRISPR-associated nuclease that functions as a potent RNA editing tool.Tetratrico-peptide repeat fused with Cas/HEF1-associated signal transducer(TPR-CHAT)acts as a regulatory protein that interacts with CRISPR RNA(crRNA)-bound Cas7-11 to form a CRISPR-guided caspase complex(Craspase).However,the precise modulation of Cas7-11’s nuclease activity by TPR-CHAT to enhance its utility requires further study.Here,we report cryo-electron microscopy(cryo-EM)structures of Desulfonema ishimotonii(Di)Cas7-11-crRNA,complexed with or without the full length or the N-terminus of TPR-CHAT.These structures unveil the molecular features of the Craspase complex.Structural analysis,combined with in vitro nuclease assay and electrophoretic mobility shift assay,reveals that DiTPR-CHAT negatively regulates the activity of DiCas7-11 by preventing target RNA from binding through the N-terminal 65 amino acids of DiTPR-CHAT(DiTPR-CHAT_(NTD)).Our work demonstrates that DiTPRCHAT_(NTD) can function as a small unit of DiCas7-11 regulator,potentially enabling safe applications to prevent overcutting and offtarget effects of the CRISPR‒Cas7-11 system.

Effect of pretreatment on Pd/Al_2O_3catalyst for catalytic oxidation of o-xylene at low temperature

The effect of pretreatment on Pd/Al2O3 catalysts for the catalytic oxidation of o-xylene at low temperature was studied by changing the pretreatment and testing conditions. The fresh and pretreated Pd/Al2O3 catalysts were characterized by transmission electron microscopy （TEM）, X-ray photoelectron spectroscopy （XPS） and X-ray diffraction （XRD）. The results showed that the pretreatment dramatically changed the Pd/PdO ratio and then significantly affected the Pd/Al2O3 activity; while the pretreatment had not much influence on Pd particle size. The Pd/Al2O3 pre-reduced at 300~C/400~C, which has fully reduced Pd species, showed the highest activity; while the fresh Pd/Al2O3, which has fully oxidized Pd species, presented the worst performance, indicating the Pd chemical state plays an important role in the catalytic activity for the o-xylene oxidation. It is concluded that metallic Pd is the active species on the Pd/Al2O3 catalyst for the catalytic oxidation of o-xylene at low temperature.

Facile synthesis of Ag-modified manganese oxide for effective catalytic ozone decomposition

O3 decomposition catalysts with excellent performance still need to be developed. In this study, Ag-modified manganese oxides(AgMnOx) were synthesized by a simple co-precipitation method. The effect of calcination temperature on the activity of MnOx and AgMnOxcatalysts was investigated. The effect of the amount of Ag addition on the activity and structure of the catalysts was further studied by activity testing and characterization by a variety of techniques. The activity of 8%AgMnOxfor ozone decomposition was significantly enhanced due to the formation of the Ag1.8 Mn8 O16 structure, indicating that this phase has excellent performance for ozone decomposition.The weight content of Ag1.8 Mn8 O16 in the 8%AgMnOxcatalyst was only about 33.76%, which further indicates the excellent performance of the Ag1.8 Mn8 O16 phase for ozone decomposition. The H2 temperature programmed reduction(H2-TPR) results indicated that the reducibility of the catalysts increased due to the formation of the Ag1.8 Mn8 O16 structure.This study provides guidance for a follow-up study on Ag-modified manganese oxide catalysts for ozone decomposition.

Detrimental role of residual surface acid ions on ozone decomposition over Ce-modified γ-MnO2under humid conditions

In the study,the catalyst precursors of Ce-modifiedγ-MnO2 were washed with deionized water until the pH value of the supernatant was 1,2,4 and 7,and the obtained catalysts were named accordingly.Under space velocity of 300,000 hr-1,the ozone conversion over the pH=7 catalyst under dry conditions and relative humidity of 65%over a period of 6 hr was 100%and 96%,respectively.However,the ozone decomposition activity of the pH=2 and 4 catalysts distinctly decreased under relative humidity of 65%compared to that under dry conditions.Detailed physical and chemical characterization demonstrated that the residual sulfate ions on the pH=2 and 4 catalysts decreased their hydrophobicity and then restrained humid ozone decomposition activity.The pH=2 and 4 catalysts had inferior resistance to high space velocity under dry conditions,because the residual sulfate ion on their surface reduced their adsorption capacity for ozone molecules and increased their apparent activation energies,which was proved by temperature programmed desorption of O2 and kinetic experiments.Long-term activity testing,X-ray photoelectron spectroscopy and density functional theory calculations revealed that there were two kinds of oxygen vacancies on the manganese dioxide catalysts,one of which more easily adsorbed oxygen species and then became deactivated.This study revealed the detrimental effect of surface acid ions on the activity of catalysts under humid and dry atmospheres,and provided guidance for the development of highly efficient catalysts for ozone decomposition.

Experimental and density functional theory study of the adsorption of N_2O on ion-exchanged ZSM-5: Part II. The adsorption of N_2O on main-group ion-exchanged ZSM-5

The adsorption and desorption of N 2 O on main-group ion-exchanged ZSM-5 was studied using temperature-programmed desorption （TPD） and density functional theory （DFT） calculations. TPD experiments were carried out to determine the desorbed temperature T max corresponding to the maximum mass intensity of N 2 O desorption peak and adsorption capacity of N 2 O on metal-ion-exchanged ZSM- 5s. The results indicated that T max followed a sequence of Ba 2＋ Ca 2＋ Cs ＋ K ＋ Na ＋ Mg 2＋ and the amount of adsorbed N 2 O on main-group metal cation followed a sequence of Ba 2＋ Mg 2＋ Ca 2＋ Na ＋ K ＋ Cs ＋ . The DFT calculations were performed to obtain the adsorption energy （E ads ）, which represents the strength of the interaction between metal cations and the N-end or O-end of N 2 O. The calculation results showed that the N-end of the N 2 O molecule was favorably adsorbed on ion-exchanged ZSM-5, except for Cs-ZSM-5. For alkali metal cations, the E ads of N 2 O on cations followed the order which was the same to that of T max ： Cs ＋ K ＋ Na ＋ . The calculated and experimental results consistently showed that the adsorption performances of alkaline-earth metal cations were better than those of alkali metal cations.

Tuning the fill percentage in the hydrothermal synthesis process to increase catalyst performance for ozone decomposition

The performance of Ce-OMS-2 catalysts was improved by tuning the fill percentage in the hydrothermal synthesis process to increase the oxygen vacancy density.The Ce-OMS-2 samples were prepared with different fill percentages by means of a hydrothermal approach(i.e.80%,70%,50%and 30%).Ce-OMS-2 with 80%fill percentage(Ce-OMS-2-80%)showed ozone conversion of 97%,and a lifetime experiment carried out for more than20 days showed that the activity of the catalyst still remained satisfactorily high(91%).For Ce-OMS-2-80%,Mn ions in the framework as well as K ions in the tunnel sites were replaced by Ce^4+,while for the others only Mn ions were replaced.O2-TPD and H2-TPR measurements proved that the Ce-OMS-2-80%catalyst possessed the greatest number of mobile surface oxygen species.XPS and XAFS showed that increasing the fill percentage can reduce the AOS of Mn and augment the amount of oxygen vacancies.The active sites,which accelerate the elimination of O3,can be enriched by increasing the oxygen vacancies.These findings indicate that increasing ozone removal can be achieved by tuning the fill percentage in the hydrothermal synthesis process.

CeO_(2)-supported Fe,Co and Ni toward CO_(2) hydrogenation:Tuning catalytic performance via metal-support interaction

The chemical transformation of CO_(2) produces carbon compounds that can be used as precursors for the production of chemicals and fuels.Here,we investigated the activity and selectivity of the transition metals(Fe,Co,and Ni)supported on CeO_(2) catalyst for CO_(2) hydrogenation at atmospheric pressure.We found that Ni/CeO_(2) shows the highest CO_(2)conversion compared with Fe/CeO_(2) and Co/CeO_(2).Besides,Co/CeO_(2)and Ni/CeO_(2) exhibit nearly 100%CH_(4)selectivity while Fe/CeO_(2) inclines to produce CO.The characterization results show that the metal-support interaction order is Fe/CeO_(2)>Co/CeO_(2)>Ni/CeO_(2),the weak metal-support inte raction over Ni/CeO_(2)benefits the activation of H_(2) and then promotes the activity of CO_(2) hydrogenation.Additionally,in situ DRIFTS results demonstrate that monodentate formate species rather than bidentate formate are the active intermediates.The main route of CO_(2) hydrogenation to CH_(4) is that CO_(2) is firstly transformed to m-HCOO*and then direct hydrogenation of the m-HCOO*to CH_(4).This study provides insights into the understanding of the mechanisms of CO_(2) hydrogenation on CeO_(2)based catalysts.

Nano-sized Ag rather than single-atom Ag determines CO oxidation activity and stability

Single-atom catalysis recently attracts great attentions,however,whether single atom or their nanoparticle(NP)has the advantage in its intrinsic activity remains under heated debate.Ag/Al_(2)O_(3) is a widely used catalyst for many catalytic reactions,while the effect of Ag particle size on the actity is seldom investigated due to the great difficulty in synthesizing single atom Ag and Ag clusters/particles with different sizes.Herein,we firstly prepared an atomically dispersed Ag/Al_(2)O_(3) catalyst using a nano-sized y-Al_(2)O_(3) as the support,subsequently obtained a series of Ag/Al_(2)O_(3) catalysts with different Ag particle sizes by H_(2) reducing single-atom Ag/Al_(2)O_(3) catalyst at various temperatures.The Ag/Al_(2)O_(3) treated at 600℃demonstrated superior CO oxidation performance over single-atom Ag/Al_(2)O_(3) and the Ag/Al_(2)O_(3) treated at 400 and 800℃.Based on experimental data and dpnsity functional theory(DFT)calculation results,we reveal that the larger Ag°particle is beneficial to oxygen activation and improves the valence stability during oxidation reaction,while the aggregation of Ag°particle also accordingly decreases the concentration of surface active sites,hence,there is an optimum Ag0 particle size.Our findings clearly confirm that Ag0nanoparticle has the advantage over single-atom Ag species in its intrinsic activity for CO oxidation.

Remarkable promotion effect of trace sulfation on OMS-2nanorod catalysts for the catalytic combustion of ethanol

OMS-2 nanorod catalysts were synthesized by a hydrothermal redox reaction method using Mn SO4（OMS-2-SO4） and Mn（CH3COO）2（OMS-2-AC） as precursors. SO4^2--doped OMS-2-AC catalysts with different SO4^2-concentrations were prepared next by adding（NH4）2SO4solution into OMS-2-AC samples to investigate the effect of the anion SO4^2-on the OMS-2-AC catalyst. All catalysts were then tested for the catalytic oxidation of ethanol. The OMS-2-SO4 catalyst synthesized demonstrated much better activity than OMS-2-AC. The SO4^2-doping greatly influenced the activity of the OMS-2-AC catalyst, with a dramatic promotion of activity for suitable concentration of SO4^2-（SO4/catalyst = 0.5% W/W）. The samples were characterized by X-ray diffraction（XRD）, field emission scanning electron microscopy（FE-SEM）, transmission electron microscopy（TEM）, X-ray photoelectron spectroscopy（XPS）,inductively coupled plasma optical emission spectroscopy（ICP-OES）, NH3-TPD and H2-TPR techniques. The results showed that the presence of a suitable amount of SO4^2-species in the OMS-2-AC catalyst could decrease the Mn–O bond strength and also enhance the lattice oxygen and acid site concentrations, which then effectively promoted the catalytic activity of OMS-2-AC toward ethanol oxidation. Thus it was confirmed that the better catalytic performance of OMS-2-SO4 compared to OMS-2-AC is due to the presence of some residual SO4^2-species in OMS-2-SO4 samples.

Antimicrobial activity of silver loaded MnO_2 nanomaterials with different crystal phases against Escherichia coli

Silver-loaded MnO_2 nanomaterials（Ag/MnO_2）,including Ag/α-MnO_2,Ag/β-MnO_2,Ag/γ-MnO_2and Ag/δ-MnO_2 nanorods,were prepared with hydrothermal and impregnation methods.The bactericidal activities of four types of Ag/MnO_2 nanomaterials against Escherichia coli were investigated and an inactivation mechanism involving Ag~＋ and reactive oxygen species（ROS）was also proposed.The bactericidal activities of Ag/MnO_2 depended on the MnO_2 crystal phase.Among these nanomaterials,Ag/β^-MnO_2 showed the highest bactericidal activity.There was a 6-log decrease in E.coli survival number after treatment with Ag/β^-MnO_2 for120 min.The results of 5,5-dimethyl-l-pyrroline-N-oxide spin-trapping measurements by electron spin resonance indicate OH and O_2^- formation with addition of Ag/β-MnO_2,Ag/γ-MnO_2 or Ag/δ-MnO_2.The strongest peak of OH appeared for Ag/β-MnO_2,while no OH or ·O_2^-signal was found over Ag/α-MnO_2.Through analysis of electron spin resonance（ESR） and Ag＋elution results,it could be deduced that the toxicity of Ag~＋ eluted from Ag/MnO_2 nanomaterials and ROS played the main roles during the bactericidal process.Silver showed the highest dispersion on the surface of β-MnO_2,which promoted ROS formation and the increase of bactericidal activity.Experimental results also indicated that Ag/MnO_2 induced the production of intracellular ROS and disruption of the cell wall and cell membrane.

Glucose production from hydrolysis of cellulose over a novel silica catalyst under hydrothermal conditions

A novel silica catalyst was synthesized by evaporation-induced self-assembly （EISA） method and tested for the catalytic selective hydrolysis of cellulose to glucose. This silica catalyst exhibited a higher catalytic activity than other oxides prepared by the same method, such as ZrO2, TiO2, and Al2O3. Using silica as a catalyst, cellulose was selectively hydrolyzed into glucose with a glucose yield as high as 50% under hydrothermal conditions without hydrogen gas. The silica catalyst was characterized by Brunauer-Emmett-Teller （BET）, X-ray diffraction （XRD） and transmission electron microscopy （TEM）. The results of temperature-programmed desorption of ammonia （NH3-TPD） and textural properties indicated that the synergistic effect between strong acidity and a suitable pore diameter of the silica catalyst may be responsible for its high activity. In addition, the catalyst was recyclable and showed excellent stability during the recycle catalytic runs.

Electrocatalytic oxidation of gaseous toluene in an all-solid cell using a foam Ti/Sb-SnO2/β-PbO_(2) anode

Mineralization of benzene,toluene,and xylene (BTX) with high efficiency at room temperature is still a challenge for the purification of indoor air.In this work,a foam Ti/Sb-Sn O2/β-Pb O_(2)anode catalyst was prepared for electrocatalytically oxidizing gaseous toluene in an all-solid cell at ambient temperature.The complex Ti/Sb-Sn O_(2)/β-Pb O_(2)anode,which was prepared by sequentially deposing Sb-Sn O_(2)and β-Pb O_(2)on a foam Ti substrate,shows high electrocatalytic oxidation efficiency of toluene (80%) at 7 hr of reaction and high CO_(2)selectivity (94.9%) under an optimized condition,i.e.,a cell voltage of 2.0 V,relative humidity of60%and a flow rate of 100 m L/min.The better catalytic performance can be ascribed to the high production rate of·OH radicals from discharging adsorbed water and the inhibition of oxygen evolution on the surface of foam Ti/Sb-Sn O_(2)/β-Pb O_(2)anode when compared with the foam Ti/Sb-Sn O_(2)anode.Our results demonstrate that prepared complex electrodes can be potentially used for electrocatalytic removal of gaseous toluene at room temperature with a good performance.

Effect of TiO_2 calcination temperature on the photocatalytic oxidation of gaseous NH_3

Carbon-modified titanium dioxide （TiO2） was prepared by a sol-gel method using tetrabutyl titanate as precursor, with calcination at various temperatures, and tested for the photocatalytic oxidation （PCO） of gaseous NH3 under visible and UV light. The test results showed that no samples had visible light activity, while the TiO2 calcined at 400℃ had the best UV light activity among the series of catalysts, and was even much better than the commercial catalyst P25. The catalysts were then characterized by X-ray diffractometry, Brunauer-Emmett-Teller adsorption analysis, Raman spectroscopy, thermogravimetry/differential scanning calorimetry coupled with mass spectrometry, ultraviolet-visible diffuse reflectance spectra, photoluminescence spectroscopy and in situ diffuse reflectance infrared Fourier transform spectroscopy. It was shown that the carbon species residuals on the catalyst surfaces induced the visible light adsorption of the samples calcined in the low temperature range （〈 300℃）. However, the surface acid sites played a determining role in the PCO of NH3 under visible and UV light over the series of catalysts. Although the samples calcined at low temperatures had very high SSA, good crystallinity, strong visible light absorption and also low PL emission intensity, they showed very low PCO activity due to their very low number of acid sites for NH3 adsorption and activation. The TiO2 sample calcined at 400℃ contained the highest number of acid sites among the series of catalysts, therefore showing the highest performance for the PCO of NH3 under UV light.

Enhancing oxidation reaction over Pt-MnO_(2) catalyst by activation of surface oxygen

Formaldehyde(HCHO) and carbon monoxide(CO) are both common air pollutants and hazardous to human body. It is imperative to develop the catalyst that is able to efficiently remove these pollutants. In this work, we activated Pt-MnO_(2)under different conditions for highly active oxidation of HCHO and CO, and the catalyst activated under CO displayed superior performance. A suite of complementary characterizations revealed that the catalyst activated with CO created the highly dispersed Pt nanoparticles to maintain a more positively charged state of Pt, which appropriately weakens the Mn-O bonding strength in the adjacent region of Pt for efficient supply of active oxygen during the reaction. Compared with other catalysts activated under different conditions, the CO-activated Pt-MnO_(2)displays much higher activity for oxidation of HCHO and CO. This research contributes to elucidating the mechanism for regulating the oxidation activity of Pt-based catalyst.

Enriching the surface oxygen as efficient anchoring site of highly dispersed Ru for enhanced hydrogenolysis activity

While supported-noble-metal catalysts have been widely investigated in hydrotreating reactions,a crucial issue that the catalytic system is still confronted with is developing an efficient approach to gain the high dispersion of noble metals under reducing conditions.In this work,Ru was supported on two MnOx with different specific surface areas(SSAs),and a much higher dispersion of Ru(83%,in contrast to 42%of the other one)was surprisingly observed over MnO with much lower SSA(around one-third of the other one).A suite of complementary characterizations demonstrates that,compared with the catalyst with high SSA(Ru/MnO-H),the MnO in the one with lower SSA(Ru/MnO-L)contains enriched surface oxygen that creates more abundant sites and bears stronger strength to anchor Ru species,mitigating the aggregation of Ru under reducing condition.This not only enriched active sites(i.e.,exposed Ru),but also created a more electron-deficient Ru domain and thus enhanced the redox property of the surface,leading to the lower barrier for C–O bond hydrogenolysis.In the hydrogenolysis of diphenyl ether,Ru/MnO-L exhibited significantly enhanced activity(i.e.,6 folds of Ru/MnO-H)and high stability.This work provides an approach to regulate the surface chemistry of support for the high dispersion of supported metal.

Effect of different reduction methods on Pd/Al_(2)O_(3) for o-xylene oxidation at low temperature

Pd/Al_(2)O_(3)was pretreated by CO,H_(2)and NaBH_(4)reduction,respectively.The reduced catalysts were tested for o-xylene oxidation and characterized by power X-ray diffraction(XRD),transmission electron microscopy (TEM),X-ray photoelectron spectroscopy (XPS) and temperature-programmed decomposition of palladium hydride (TPDH).The characterizations indicate the pretreatments lead to distinct Pd particle sizes and amount of surface activated oxygen species,which are responsible for the catalytic performance.Compared with H_(2)and NaBH_(4)reduction methods,CO reduction shows a strong interaction between Pd and Al_(2)O_(3)with smaller Pd particle size and more surface activated oxygen.It exhibited excellent catalytic performance,complete oxidation of 50 ppmV o-xylene at 85℃with a WHSV of 60,000 mL/(g·hr).

Photocatalysis and ambient catalysis for environmental remediation

Environmental pollution is a major challenge faced by human beings, and is becoming more serious due to increasing urbanization and industrialization. Catalysis is the key technology for environmental remediation. As a “green” technology, photocatalysis and ambient catalysis could offer numerous opportunities to realize environmental remediation under mild reaction conditions with low energy input. Over the past two decades, great advances have been made on the design and synthesis of the photocatalysts and ambient catalysts, precise control of catalyst active sites, and the mechanistic understanding on the catalytic process for environmental remediation.