A Hypothesis Regarding the Origin of Additional Surface Acidity in Solid Complexes with Same Metal Cations

Based on the criteria for additional surface acidity generation in composite oxides and composite fluorides proposed by Tanabe and Kemnitz et al.A hypothesis for the origin of additional surface acidity in solid composites with the same metal cations is proposed.The surface acidsites of We analyze three types of solid composite systems,that is,CrF_(3)/Cr_(2)O_(3),MgF_(2)/MgO,and ZnF_(2)/ZnO,is systematically analyzed,which agrees with experimental results.Accordingly,the origin of additional surface acidity in these solid composites is reasonably explained,and the types of acidic sites are also predicted.

Surface Acidity of Amorphous Aluminum Hydroxide

The surface acidity of synthetic amorphous AI hydroxide was determined by acid/base titration with several complementary methods including solution analyses of the reacted solutions and XRD characterization of the reacted solids. The synthetic specimen was characterized to be the amorphous material showing four broad peaks in XRD pattern. XRD analyses of reacted solids after the titration experiments showed that amorphous AI hydroxide rapidly transformed to crystalline bayerite at the alkaline condition （pH〉10）. The solution analyses after and during the titration Ksp=^aAl^3＋/aH^＋^3 ,was 10^10.3. The amount of consumption of added acid or base during the titration experiment was attributed to both the protonation/deprotonation of dissolved AI species and surface hydroxyl group. The surface acidity constants, surface hydroxyl density and specific surface area were estimated by FITEQL 4.0.

Sorption of a triazol derivative by soils: importance of surface acidity

The sorption of a triazol derivative, 1-(4-chlorophenyl)- 4,4-dimethyl-2-(1H-1,2,4-triazol-1-yl)penten-3-ol with a common name of S3307D, on fifteen soils and three H_2O_2-treated soils was investigated. The sorption isotherm for each untreated and treated soil was non-linear, and was best fitted to Freundlich sorption equation. Soils containing high amount of clay content or organic matter or both sorbed much higher amounts of the chemical than soils that had low contents of these soil constituents. H_2O_2-treated soils showed considerable sorptive affinity for S3307D. It was concluded that both organic matter and mineral fraction in natural soils contributed to the sorption of the basic compound. Sorption by the H_2O_2 treated soils increased as suspension pH decreased, but all suspension pHs exceeded the pKa of the compound by more than two units. This implies that organic base protonation can occur on surfaces of soil components, and surface acidity (exchangeable acidity ) is important in sorption process of the organic base rather than suspension pH.

A highly active VOx-MnOx/CeO_(2) for selective catalytic reduction of NO:The balance between redox property and surface acidity

Excellent catalysts with low-temperature activity and relatively wide temperature window for selective catalytic reduction of NO with ammonia(NH_(3)-SCR) are highly demanded in view of the practical treatment of NO.Herein,we have designed a highly active VOx-MnOx/CeO_(2) material based on the intrinsic requirement of SCR reaction for catalyst,namely redox sites and surface acid sites.The vanadium oxide and manganese oxide are highly dispersed over the ceria mesosphere via simple incipient wetness impregnation.The loading of manganese could introduce acid sites and enhance the redox property remarkably,while the loading of vanadium increases acid sites and weakens redox property.Through tentatively controlling the appropriate loading ratio of the two components,the optimal catalyst achieves a balance between redox property and surface acidity.The work shed light on the development of new SCR catalyst with superior low temperature activity,wide work temperature window and good hydrothermal stability.

Separation of galena and chalcopyrite using the difference in their surface acid corrosion characteristics

Galena(PbS)and chalcopyrite(CuFeS_(2))are sulfide minerals that exhibit good floatability characteristics.Thus,efficiently separating them via common flotation is challenging.Herein,a new method of surface sulfuric acid corrosion in conjunction with flotation separation was proposed,and the efficient separation of galena and chalcopyrite was successfully realized.Contact angle test results showed a substantial decrease in surface contact angle and a selective inhibition of surface floatability for corroded galena.Meanwhile,the contact angle and floatability of corroded chalcopyrite remained almost unaffected.Scanning electron microscope results confirmed that sulfuric acid corrosion led to the formation of a dense oxide layer on the galena surface,whereas the chalcopyrite surface remained unaltered.X-ray photoelectron spectroscopy results showed that the chemical state of S^(2-)on the surface of corroded galena was oxidized to SO_(4)^(2-).A layer of hydrophilic PbSO4was formed on the surface,leading to a sharp decrease in galena floatability.Meanwhile,new hydrophobic CuS_(2),CuS,and Cu_(1-x)Fe_(1-y)S_(2-z)species exhibiting good floatability were generated on the chalcopyrite surface.Finally,theoretical analysis results were further verified by corrosion–flotation separation experiments.The galena–chalcopyrite mixture was completely separated via flotation separation under appropriate corrosion acidity,corrosion temperature,and corrosion time.A novel approach has been outlined in this study,providing potential applications in the efficient separation of refractory copper–lead sulfide ore.

Enhanced low-temperature NH3-SCR performance of CeTiOx catalyst via surface Mo modification

The effect of molybdenum oxide on the activity and durability of Ce O2-Ti O2 catalyst for NO reduction by NH3 was examined. It was found that the introduction of Mo could improve the low-temperature NH3-SCR activity and SO2/H2 O durability of the Ce O2-Ti O2 catalyst and an optimal loading of Mo was 4?wt.%. The best Mo O3/Ce O2-Ti O2 catalyst displayed over 90% NO conversion from 200 °C to 400 °C and obtained 4-fold increase in NO conversion compared to Ce O2-Ti O2 at 150 °C. The characterization results revealed that the number of Br?nsted acid sites over Mo O3/Ce O2-Ti O2 was significantly increased, and the adsorption of nitrate species was dramatically weakened because of the coverage of Mo O3, which were favorable for the high NH3-SCR performance. It is believed that the Mo O3/Ce O2-Ti O2 catalyst is a suitable substitute for the NH3-SCR reaction.

Effect of TiO_2 surface properties on the SCR activity of NOx emission abatement catalyst

NOx emission abatement catalysts V 2O 5 supported on various TiO 2 including anatase, rutile and mixture of both were investigated with various physico\|chemical measurements such as BET, NH\-3\|TPD, NARP, XRD and so on, and the effect of TiO\-2 surface properties on the SCR(selective catalytic reduction) activity of V\-2O\-5/TiO\-2 catalysts was studied. It was found that the TiO\-2 surface properties had strong affect on the SCR activity of V\-2O\-5/TiO\-2 catalysts. The stronger acidic property resulted in the higher exposure of active sites as well as the higher SCR activity.

Proton Dissociation from Surfaces of Variable Charge Soil andMnierals

Experiments on proton dissociation from the surfaces of goethite, amorphous Al oxide, kaolinite and latosolwere carried out, showing amphoteric behavior with reactions of proton dissociation-association on the surfaces andbuffering capacity in such a sequence as amorphous Al oxide > latosol > kaolinite > goethite. Dissociation con-stants of surface proton, pK_(sa) are significantly correlated with surface charge density, which has been proved with anelectrochemical model. Tbe intrinsic constants of proton dissociation, K_(sa)(int), gained by extrapolation to zero charconditions of plots of pK_(sa) against σ_o, could be used to estimate the acidity strength of variable charge surfaces. Thevalue of pK_(sa)(int) is 8.08 for goethite, 1 .2 for amorphous Al oxide, 6.62 for kaolinite and 5 .32 for latosol.

Zr（Ⅳ） surface sites determine CH3OH formation rate on Cu/ZrO2/SiO2-CO2 hydrogenation catalysts

Cu/ZrO2/SiO2 are efficient catalysts for the selective hydrogenation of CO2 to CH3OH. In order to understand the role of ZrO2 in these mixed-oxides based catalysts, in situ X-ray absorption spectroscopy has been carried out on the Cu and Zr K-edge. Under reaction conditions, Cu remains metallic, while Zr is present in three types of coordination environment associated with 1) bulk ZrO2, 2) coordinatively saturated and 3) unsaturated Zr(Ⅳ) surface sites. The amount of coordinatively unsaturated Zr surface sites can be quantified by linear combination fit of reference X-Ray absorption near edge structure (XANES) spectra and its amount correlates with CH3OH formation rates, thus indicating the importance of Zr(Ⅳ) Lewis acid surface sites in driving the selectivity toward CH3OH. This finding is consistent with the proposed mechanism, where CO2 is hydrogenated at the interface between the Cu nanoparticles that split H2 and Zr(Ⅳ) surface sites that stabilizes reaction intermediates.

One Novel 2D Co(Ⅱ) Polymer with 1,2,3-Triazole Derivative: Crystal Structure, Fluorescence and Hirshfeld Surface Analysis

One new polymer [Co（L）（H2O）2]n（1） was synthesized by 4-（ethoxycarbonyl）-5-methyl-1H-1,2,3-triazole-1-carboxylic acid（Emtc） under the in situ solvent thermal reaction（H2L = 1-（carboxymethyl）-5-methyl-1H-1,2,3-triazole-4-carboxylic acid）. The title complex performs a wave-like 2D framework and the ligand H2L demonstrates the coordination mode as μ4-η-2：η-1η-1：η-1. The crystal structure has been established by single-crystal X-ray diffraction, and characterized by FT-IR. Fluorescent property was investigated in this work. Hirshfeld surface analysis has also been carried out on 1, and obvious main intermolecular interactions are observed.

Novel Perchlorate and Sulphate Salts of 2-Aminonicotinic Acid:Synthesis,Characterization,Thermal Studies and Hirshfeld Surface Analysis

Since 2-aminonicotinic acid is a zwitterionic molecule,the salt or co-crystal strategy was used for the precipitation under identical conditions and obtained two novel salts： salt 1 with 2：1：2 stoichiometry of 2-aminonicotinic acid：perchloric acid：H2O and salt 2 with 2：1：3 stoichiometry of 2-aminonicotinic acid：sulfuric acid：H2O. Their crystal structures were characterized by single-crystal X-ray diffraction,differential scanning calorimetry（DSC） and thermogravimetric analyses（TGA）. The structure determination shows that two salts are both primarily stabilized by the strong N–H…O hydrogen bonding interaction between 2-aminonicotinic acid and its corresponding acids. Constituents of the salt-crystalline phase were also investigated in terms of Hirshfeld surfaces. In the crystal lattice,a three-dimensional hydrogen-bonded network is observed,including the formation of a two-dimensional molecular scaffolding motif. Hirshfeld surfaces and fingerprint plots of two salts show that the structures are stabilized by H…H,O–H…O and C–O…π intermolecular interactions.

Enhancement of gaseous mercury(Hg^0) adsorption for the modified activated carbons by surface acid oxygen function groups

This article discussed the benzoic acid activated carbons which have changed the types and content of acid oxygen-function groups on the surface of activated carbons and their effect on the adsorption for Hg^0 in simulated flue gas at 140 ℃. These surface acid oxygen function groups were identified by Boehm titration, Fourier transformation infrared spectrum, temperature programmed desorption and X-ray photoelectron spectroscopy. It indicates that the carboxyl, lactone and phenolic were formed when the benzoic acid is loaded on the surface of activated carbons. Among the surface acid oxygen function groups, the carboxyl groups enhance the adsorption capacities of Hg^0 for activated carbons to a greater extent.

Surface Modification of Natural Fibrous Brucite with Stearic Acid

Fibrous brucite,a kind of brucite with unique structure and physical properties,was modified with stearic acid as a surface modifier.In order to investigate the mechanism of surface modification,the fixation of stearic acid on fibrous brucite and the induced changes in surface properties were studied by using X-ray diffraction（XRD）,scanning electron microscopy（SEM）,infrared spectroscopy（IR）,Raman spectroscopy and thermo-gravimetric analysis（TGA）.XRD analysis indicates that the modification of fibrous brucite with stearic acid does not cause any changes in the structure of fibrous brucite mineral.Spectroscopy and thermal analysis show that the surfactant molecules are not only directly adsorbed on the surface of the mineral,but also chemisorbed on mineral surface by forming chemical bonds between the modifier and magnesium hydroxide.

Flame Synthesis of Zr/ZSM-5 Catalysts with Tunable Acidity for the Oxidative Dehydrogenation of Propane to Propene

Tuning the surface acidity of ZSM-5 catalyst is essential to achieve desired propene selectivity and yield.Here several ratios of Zr were utilized to modify ZSM-5 via flame spray pyrolysis technique coupled with a pulse spray evaporation system.The interaction between Zr and ZSM-5 in the flame influenced the physicochemical and acidity properties of the Zr/ZSM-5.The increasing Zr ratio in ZSM-5 shows coated layers of irregular nano-sized Zr with an increase in crystallite sizes due to the synergetic effect between Zr and ZSM-5.The surface chemical analysis revealed increased lattice oxygen on the Zr modified ZSM-5(1:4) sample compared to other catalysts.The acidity analysis revealed the Lewis and Br?nsted acid distribution in the weak and medium acid sites on the catalyst surface.However,the increase in Zr loading decreased the concentration of Br?nsted acid sites and tuned the catalyst surface to more Lewis acidity,promoting propene selectivity and hindering the over-oxidation of propene.The modified ZSM-5 catalysts were examined in a fixed bed reactor within 300℃-700℃ at a gas hourly space velocity(GHSV) of 6000 mL·g(catalysts)^(-1)·h^(-1) for the oxidative dehydrogenation of propane(ODHP) to propene.Among the catalysts,Zr/ZSM-5(1:4) exhibited the best propene yield, with 57.19% propane conversion and 75.54% selectivity to propene and the highest stability.This work provides a promising strategy for tuning the surface acidity of ZSM-5 with Zr for ODHP applications.

Influence of preparation methods on the physicochemical properties and catalytic performance of MnO_x-CeO_2 catalysts for NH_3-SCR at low temperature

This work examines the influence of preparation methods on the physicochemical properties and catalytic performance of MnOx‐CeO2 catalysts for selective catalytic reduction of NO by NH3 (NH3‐SCR) at low temperature. Five different methods, namely, mechanical mixing, impregnation,hydrothermal treatment, co‐precipitation, and a sol‐gel technique, were used to synthesizeMnOx‐CeO2 catalysts. The catalysts were characterized in detail, and an NH3‐SCR model reaction waschosen to evaluate the catalytic performance. The results showed that the preparation methodsaffected the catalytic performance in the order: hydrothermal treatment > sol‐gel > co‐precipitation> impregnation > mechanical mixing. This order correlated with the surface Ce3+ and Mn4+ content,oxygen vacancies and surface adsorbed oxygen species concentration, and the amount of acidic sitesand acidic strength. This trend is related to redox interactions between MnOx and CeO2. The catalystformed by a hydrothermal treatment exhibited excellent physicochemical properties, optimal catalyticperformance, and good H2O resistance in NH3‐SCR reaction. This was attributed to incorporationof Mnn+ into the CeO2 lattice to form a uniform ceria‐based solid solution (containing Mn‐O‐Cestructures). Strengthening of the electronic interactions between MnOx and CeO2, driven by thehigh‐temperature and high‐pressure conditions during the hydrothermal treatment also improved the catalyst characteristics. Thus, the hydrothermal treatment method is an efficient and environment‐friendly route to synthesizing low‐temperature denitrification (deNOx) catalysts.

Support effect of the supported ceria-based catalysts during NH_3-SCR reaction

To investigate how the physicochemical properties and NH3‐selective catalytic reduction(NH3‐SCR)performance of supported ceria‐based catalysts are influenced as a function of support type,a series of CeO2/SiO2,CeO2/γ‐Al2O3,CeO2/ZrO2,and CeO2/TiO2catalysts were prepared.The physicochemical properties were probed by means of X‐ray diffraction,Raman spectroscopy,Brunauer‐Emmett‐Teller surface area measurements,X‐ray photoelectron spectroscopy,H2‐temperature programmed reduction,and NH3‐temperature programmed desorption.Furthermore,the supported ceria‐based catalysts'catalytic performance and H2O+SO2tolerance were evaluated by the NH3‐SCR model reaction.The results indicate that out of the supported ceria‐based catalysts studied,the CeO2/γ‐Al2O3catalyst exhibits the highest catalytic activity as a result of having a high relative Ce3+/Ce4+ratio,optimum reduction behavior,and the largest total acid site concentration.Finally,the CeO2/γ‐Al2O3catalyst also presents excellent H2O+SO2tolerance during the NH3‐SCR process.

Low-temperature activity and mechanism of WO_3-modified CeO_2-TiO_2 catalyst under NH_3-NO/NO_2 SCR conditions

The CeO2‐TiO2(CeTi)and CeO2/WO3‐TiO2(CeWTi)catalysts were prepared by a sol‐gel precipitation method and their NH3‐NO/NO2 selective catalytic reduction(SCR)performance was studied.N2O formation and effect of oxygen concentration on SCR performance over CeWTi catalyst were also investigated while varying the NO2/NOx ratio.Results indicate that fast SCR behavior of CeWTi catalyst has the best NH3‐NO/NO2 SCR performance due to the catalyst reoxidation rate by NO2 higher than by O2.Compared with CeTi catalyst,CeWTi catalyst exhibits higher de‐NOx performance under NH3‐NO/NO2 SCR conditions.As the CeTi and CeWTi catalysts exhibit similar redox property,addition of WO3 provides more acid sites which accelerate the reaction between NH4NO3 and NO to get a superior low‐temperature activity.Amount of N2O formation shows a peak at 250 oC mainly derived from NH4NO3 decomposition.

The effect of cations(NH_4^+,Na^+,K^+,and Ca^(2+)) on chemical deactivation of commercial SCR catalyst by bromides

Alkali and alkaline‐earth metals from fly ash have a significant deactivation effect on catalysts used for selective catalytic reduction of NOx by NH3(NH3‐SCR).Bromides are considered effective additives to improve Hg0 oxidation on SCR catalysts.In this work,the effects of different bromides(NH4Br,NaBr,KBr,and CaBr2)on a commercial V2O5‐WO3/TiO2 catalyst were studied.NOx conversion decreased significantly over the KBr‐poisoned catalyst(denoted as L‐KBr),while that over NaBr‐and CaBr2‐poisoned catalysts(denoted as L‐NaBr and L‐CaBr,respectivity)decreased to a lesser extent compared with the fresh sample.Poor N2 selectivity was observed over L‐NaBr,L‐KBr and L‐CaBr catalysts.The decrease in the ratio of chemisorbed oxygen to total surface oxygen(Oα/(Oα+Oβ+Ow)),reducibility and surface acidity might contribute to the poor activity and N2 selectivity over L‐KBr catalyst.The increased Oαratio was conducive to the enhanced reducibility of L‐CaBr.Combined with enhanced surface acidity,this might offset the negative effect of the loss of active sites by CaBr2 covering.The overoxidation of NH3 and poor N2 selectivity in NH3 oxidation should retard the SCR activity at high temperatures over L‐CaBr catalyst.The increased basicity might contribute to increased NOx adsorption on L‐KBr and L‐CaBr catalysts.A correlation between the acid‐basic and redox properties of bromide‐poisoned catalysts and their catalytic properties is established.

Doping effect of cations(Zr^(4+),Al^(3+),and Si^(4+)) on MnO_x/CeO_2 nano-rod catalyst for NH_3-SCR reaction at low temperature

Thermally stable Zr4+, Al3+, and Si4+ cations were incorporated into the lattice of CeO2 nano‐rods (i.e., CeO2‐NR) in order to improve the specific surface area. The undoped and Zr4+, Al3+, and Si4+ doped nano‐rods were used as supports to prepare MnOx/CeO2‐NR, MnOx/CZ‐NR, MnOx/CA‐NR, and MnOx/CS‐NR catalysts, respectively. The prepared supports and catalysts were comprehensively characterized by transmission electron microscopy (TEM), high‐resolution TEM, X‐ray diffraction, Raman and N2‐physisorption analyses, hydrogen temperature‐programmed reduction, ammonia temperature‐programmed desorption, in situ diffuse reflectance infrared Fourier‐transform spectroscopic analysis of the NH3 adsorption, and X‐ray photoelectron spectroscopy. Moreover, the catalytic performance and H2O+SO2 tolerance of these samples were evaluated through NH3‐selective catalytic reduction (NH3‐SCR) in the absence or presence of H2O and SO2. The obtained results show that the MnOx/CS‐NR catalyst exhibits the highest NOx conversion and the lowest N2O concentration, which result from the largest number of oxygen vacancies and acid sites, the highest Mn4+ content, and the lowest redox ability. The MnOx/CS‐NR catalyst also presents excellent resistance to H2O and SO2. All of these phenomena suggest that Si4+ is the optimal dopant for the MnOx/CeO2‐NR catalyst.

Co–Cr–O mixed oxides for low–temperature total oxidation of propane: Structural effects, kinetics, and spectroscopic investigation

A series of Co–Cr–O mixed oxides with different Co/Cr molar ratios are synthesized and tested for the total oxidation of propane.The reaction behaviors are closely related to the structural features of the mixed oxides.The catalyst with a Co/Cr molar ratio of 1:2(1 Co2 Cr)and a spinel structure has the best activity(with a reaction rate of 1.38μmol g^–1 s^–1 at 250℃),which is attributed to the synergistic roles of its high surface acidity and good low-temperature reducibility,as evidenced by the temperature-programmed desorption of ammonia,reduction of hydrogen,and surface reaction of propane.Kinetic study shows that the reaction orders of propane and oxygen on the 1 Co2 Cr catalyst(0.58±0.03 and 0.34±0.05,respectively)are lower than those on the 2 Co1 Cr catalyst(0.77±0.02 and 0.98±0.16,respectively)and 1 Co5 Cr(0.66±0.05 and 1.30±0.11,respectively),indicating that the coverages of propane and oxygen on 1 Co2 Cr are higher than those on the other catalysts due to its higher surface acidity and higher reducibility.In addition,in-situ diffuse reflectance infrared spectroscopic investigation reveals that the main surface species on 1 Co2 Cr during the reaction are polydentate carbonate species,which accumulate on the surface at low temperatures(<250℃)but decompose at relatively high temperatures.