Strong Surface Acidity Research Articles

Highly dispersed V2O5/TiO2 modified with transition metals (Cu, Fe, Mn, Co) as efficient catalysts for the selective reduction of NO with NH3

Different transition metals were used to modify V2O5-based catalysts (M-V, M = Cu, Fe, Mn, Co) on TiO2 via impregnation, for the selective reduction of NO with NH3. The introduced metals induced high dispersion in the vanadium species and the formation of vanadates on the TiO2 support, and increased the amount of surface acid sites and the strength of these acids. The strong acid sites might be responsible for the high N2 selectivity at higher temperatures. Among these catalysts, Cu-V/TiO2 showed the highest activity and N2 selectivity at 225–375 °C. The results of X-ray photoelectron spectroscopy, NH3-temperature-programmed desorption, and in-situ diffuse reflectance infrared Fourier transform spectroscopy suggested that the improved performance was probably due to more active surface oxygen species and increased strong surface acid sites. The outstanding activity, stability, and SO2/H2O durability of Cu-V/TiO2 make it a candidate to be a NOx removal catalyst for stationary flue gas.

Preparation and adsorption properties of the biomimetic gama-alumina

Biomimetic gama-alumina was prepared by using broadleaf Liriope leaf as template. The surface acidity of the sample was measured and the adsorption experiments were carried out. The results indicated that the obtained gama-alumina inherited the morphology and microstructure of leaf template and showed weak surface acidity. Therefore, the as-prepared alumina exhibited good adsorption performance for acid fuchsin, but bad adsorption toward alkaline methyl orange. After acid-modifying, the sample showed strong surface acidity and displayed good adsorption performance toward alkaline methyl orange. These results demonstrated that the surface acidity-alkalinity of alumina determined its adsorption performance and selectivity for organic compounds.

Performance of RP-3 kerosene cracking over Pt/WO3–ZrO2 catalyst

A series of WO3–ZrO2 composite oxides were prepared by co-precipitation and their catalytic performances for the RP-3 kerosene cracking were investigated. These composite oxides were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), N2 adsorption–desorption measurement, X-ray diffraction (XRD), and NH3-temperature programmed desorption (NH3-TPD). The results showed that the addition of WO3 could effectively inhibit the phase transformation of ZrO2 from tetragonal phase to monoclinic phase. Among all as-prepared samples, the support composed of WO3 (4wt%)–ZrO2 exhibited the largest surface area, the strongest surface acidity, and the most concentrated strong acidic density. Additionally, the gas amount of catalytic cracking over Pt/WO3 (4wt%)–ZrO2 catalyst at the temperature region 650–700°C was about 1.5 times higher than that of thermal cracking. After the composite oxides were calcined at 800°C for 3h, they almost lost their catalytic activities.

Effect of strong acid functional groups on electrode rise potential in capacitive mixing by double layer expansion.

The amount of salinity-gradient energy that can be obtained through capacitive mixing based on double layer expansion depends on the extent the electric double layer (EDL) is altered in a low salt concentration (LC) electrolyte (e.g., river water). We show that the electrode-rise potential, which is a measure of the EDL perturbation process, was significantly (P = 10(–5)) correlated to the concentration of strong acid surface functional groups using five types of activated carbon. Electrodes with the lowest concentration of strong acids (0.05 mmol g(–1)) had a positive rise potential of 59 ± 4 mV in the LC solution, whereas the carbon with the highest concentration (0.36 mmol g(–1)) had a negative rise potential (−31 ± 5 mV). Chemical oxidation of a carbon (YP50) using nitric acid decreased the electrode rise potential from 46 ± 2 mV (unaltered) to −6 ± 0.5 mV (oxidized), producing a whole cell potential (53 ± 1.7 mV) that was 4.4 times larger than that obtained with identical electrode materials (from 12 ± 1 mV). Changes in the EDL were linked to the behavior of specific ions in a LC solution using molecular dynamics and metadynamics simulations. The EDL expanded in the LC solution when a carbon surface (pristine graphene) lacked strong acid functional groups, producing a positive-rise potential at the electrode. In contrast, the EDL was compressed for an oxidized surface (graphene oxide), producing a negative-rise electrode potential. These results established the linkage between rise potentials and specific surface functional groups (strong acids) and demonstrated on a molecular scale changes in the EDL using oxidized or pristine carbons.

Synthesis of high-surface-area Co-O-Si complex oxide for skeletal isomerization of 1-hexene and hydrodesulfurization of thiophene

The coprecipitation of sodium silicate with cobalt nitrate, combined with an n-butanol drying process, led to the formation of a Co-O-Si complex oxide (Co/Si atomic ratio ≈ 0.65) with atomically dispersed Co and Si atoms. The complex oxide had a high surface area (562 m2/g) and strong surface acidity. Sulfidation resulted in the formation of highly dispersed cobalt sulfide, which had high activity in the hydrodesulfurization (HDS) of thiophene (99.4%) and skeletal isomerization of 1-hexene (35%) at 573 K. The HDS activity was as high as that of the industrial catalyst Co-Mo/γ-Al2O3, although no Mo was present. The material could therefore be used for the skeletal isomerization of linear olefins during deep HDS of gasoline to reduce octane number loss caused by olefin saturation.

Sulfonated carbon materials with hydrophilic and lipophilic properties

Two acidic carbon materials (H-PRC and HS-C) were used as catalysts for the condensation reaction of methanol with formaldehyde to produce dimethoxymethane (DMM) in aqueous solution (hydrophilic system) and for the etherification of isopentene with methanol to produce tert amyl methyl ether (TAME) in toluene solution (lipophilic system). Microcalorimetric adsorptions of water and benzene showed that the HS-C was highly hydrophilic without the lipophilicity, while the H-PRC exhibited both the hydrophilicity and lipophilicity. Thus, the HS-C was well dispersed in aqueous solution and difficult to separate from it. On the other hand, the H-PRC was highly active, more active than the acidic resin (D008) and sulfuric acid, for the synthesis of DMM in aqueous solution. The H-PRC was also highly active, more active than the HS-C, for the etherification of isopentene with methanol to produce TAME in toluene solution, probably owing to its amphiphilic surface property as well as its strong surface acidity as measured by the microcalorimetric adsorption of NH3.

A Physicochemical Evaluation of Modified HZSM-5 Catalyst Utilized for Production of Dimethyl Ether From Methanol

A number of HZSM-5 catalysts modified with 5 wt% Mg, Na, Zr, and Al as well as others modified with 5–60 wt% Zn prepared by wet impregnation. These materials were characterized by the NH3-TPD, XRF, and XRD analyses and tested in a slurry reactor to determine their activities in dehydration of methanol solution in kerosene. Reactions were carried out at 230°C and 19 bar for 4 h of residence time in the reactor. Results showed that in the first series, the catalyst modified with Zr and in the second series, the one modified with 10 wt% Zn led to the highest methanol conversion. It was deduced that elimination of strong acid sites and partial replacement of active cations in the HZSM-5 zeolite lattice enhanced the performance and improved resistance against formation of hydrocarbons and other by-products such as olefins all of which acted as coke precursors. In order to determine the activation energy, the rate equation of Bercic and Levec was utilized and assumptions consistent with reaction conditions considered. Hence, rate constants determined empirically through fitting experimental data to the aforementioned rate equation. Ultimately, the related activation energies were calculated. In comparison with common dehydration catalysts such as alumina, the activation energies of the modified catalyst decreased. Nonetheless, the superior performance of the modified HZSM-5 attributed mainly to the elimination of strong surface acid sites by partial substitution of cations resulted in prevention of coke and undesired hydrocarbon formation.

The performance of Pt/ZrxTixAl1–2xO2 as Kerosene cracking catalysts

Zr x Ti x Al 1–2 x O 2 composite oxides for use as supports were prepared by coprecipitation and assessed with regard to their catalytic performance during the kerosene cracking reaction. The catalysts were characterized by N 2 adsorption-desorption, scanning electron microscopy-energy dispersive spectrometry, X-ray diffraction, and temperature-programmed desorption (NH 3 -TPD). The results showed that a support composed of ZrO 2 :TiO 2 :Al 2 O 3 in the ratio of 1:1:3 exhibited the highest surface area and pore volume, and had the strongest surface acidity and highest acidic density. Energy dispersive spectroscopy results showed that catalysts from which carbon deposits were removed by heating under oxygen changed very little, and additional experimental data confirmed that these catalysts are readily regenerated while retaining their functionality. The gaseous reaction products produced over ZrO 2 :TiO 2 :Al 2 O 3 (1:1:3)-supported Pt catalyst generated during catalytic cracking was 2.1 times and 1.4 times higher than that obtained with thermal cracking at 650 °C and 700 °C, respectively. An examination of the catalytic performance of Pt catalyst supported on composite oxides calcined at 1000 °C for 5 h indicated that these materials lost much of their catalytic activity. A series of Pt/Zr x Ti x Al 1–2 x O 2 catalysts were prepared and they showed good performance for the kerosene cracking reaction. The quantities of gaseous products obtained from catalytic cracking using ZrO 2 :TiO 2 :Al 2 O 3 (1:1:3)- supported Pt catalyst are increased by factors of 2.1 and 1.4 compared with the quantities generated by thermal cracking at 650 and 700 °C, respectively.

Catalytic behaviour of a bifunctional system for the one step synthesis of DME by CO2 hydrogenation

One-step CO2 hydrogenation reaction to dimethyl ether (DME) on a bifunctional system constituted by Cu–ZnO–ZrO2 (ZCZ) methanol synthesis catalyst and HZSM-5 zeolite was studied. The influence of the reactor configuration in terms of combination procedure of the admixed samples on activity, selectivity and DME yield has been evaluated. The results obtained at TR=513K, PR=3.0MPa and GHSV=9000NLgcat−1h−1 show a superior DME productivity (4.4mmolkgZCZ−1s−1) using the bifunctional catalyst prepared by physical mixing. A combined effect of active sites located at metal/oxide(s)–acid interface was claimed as the main factor affecting the CO2 conversion and DME productivity. The strong surface acidity of ZCZ catalyst is not suitable to drive DME synthesis through a consecutive mechanism, while DME formation effectively proceeds on weak and medium acid sites of HZSM-5.

Etherification of glycerol and isobutylene catalyzed over rare earth modified Hβ-zeolite

Rare earth (RE) modified Hβ-zeolites were prepared by ion exchange with various rare earth cations (La3+, Ce3+, Nd3+ and Eu3+), and investigated for the etherification of glycerol with isobutylene to synthesize glycerol ethers. XRD, EDS, BET and NH3-TPD analysis methods had been used to characterize these catalysts. The analytic results indicate that the surface strong acidity was enhanced by RE-ion exchange while the framework structure of Hβ-zeolites was slightly changed. Among all modified Hβ-zeolites, Nd/Hβ-zeolite had the highest quantity of Brönsted acid sites which would be helpful for etherification, and exhibited the best catalytic performance. Under the optimal reaction conditions of isobutylene to glycerol of 3:1, a catalyst-to-glycerol mass ratio of 6wt.%, a reaction temperature of 343K, and a reaction time of 2h, 92% glycerol was transformed into a mixture of glycerol ethers including mono-tert-butyl ethers of glycerol (MTBGs), di-tert-butyl ethers of glycerol (DTBGs) and tri-tert-butyl ether of glycerol (TTBG). The selectivity toward the desired DTBG and TTBG were 65% and 8%, respectively.

Structural Properties of MnO<em><sub>x</sub></em>/Al-SBA-15 in Low-Temperature Selective Catalytic Reduction of NO<em><sub>x</sub></em> with NH<sub>3</sub>

A series of MnO x /Al-SBA-15 catalysts were prepared by post synthesis methods for lowtemperature selective catalytic reduction (SCR) of NOx with NH3.Structural properties and catalytic performance were comprehensively characterized by Fourier transform infrared (FTIR) spectroscopy,N2 adsorption-desorption,X-ray powder diffraction (XRD),scanning electron microscopy (SEM),Raman spectroscopy,X-ray photoelectron spectroscopy (XPS),and temperature programmed desorption of NH 3 (NH 3-TPD).The results showed that moderate addition of Al improved the SCR activity of the MnO x /SBA-15 catalyst,and the MnO x /Al-SBA-15 catalyst with n Si /n Al =50 had the highest activity.Characterization results revealed that the doped material MnOx /Al-SBA-15 catalysts maintained high specific surface area,large pore volume,and uniform pore size.Al doping improved the concentration and valence state of Mn,where MnO2 was determined to be the main active phase.Owing to a high dispersion of MnO x and a stronger surface acidity,the MnOx /Al(50)-SBA-15 catalyst exhibited higher SCR activity.

The effects of surface acidity on CO2 adsorption over amine functionalized protonated titanate nanotubes

In this paper, an infrared study has been performed on CO2 adsorption over polyethylenimine (PEI) functionalized protonated titanate nanotubes (PTNTs) prepared by a simple wet impregnation method. It was found that PTNTs had a large amount of acidity sites, which had strong interaction with the amino groups of the loaded PEI. This interaction could lead to good dispersion of PEI molecules, resulting in good performance in adsorption capacity, amine efficiency and adsorption kinetics. Both weakly and strongly adsorbed CO2 species formed under CO2 exposure, which were attributed to hydrogen-bonded species and carbamate groups, respectively. The existence of strong surface acidity increased the proportion of weakly adsorbed CO2 on the protonated amine species, which was beneficial to the adsorption–desorption cyclic performance. Furthermore, it was confirmed that the interaction between the support surface and amine also resulted in the superior thermal stability of amine-modified sorbents. Overall, our results suggested that suitably tuning surface acidity of the support could effectively facilitate CO2 adsorption.

The effect of surface acidic and basic properties on the hydrogenation of lauronitrile over the supported nickel catalysts

Supported nickel catalysts with different supports (MgO, SiO2, Al2O3, MgAlO and SiAlO) were prepared by the co-precipitation method and dried in n-butanol. Nickel was found to be relatively easier to reduce in Ni/MgO and Ni/SiO2 than in Ni/Al2O3, while nickel was higher dispersed in Ni/SiO2 than in Ni/Al2O3 and Ni/MgO. Thus, the reducibility and dispersion of nickel in Ni/MgAlO and Ni/SiAlO were significantly enhanced, leading to the high active nickel surface areas (75m2/g-catalyst). Acetonitrile was found to be adsorbed on the reduced nickel and acidic sites. The strong surface basicity of Ni/MgO was found to favor the selectivity to the primary amine, but inhibited the conversion of lauronitrile. On the other hand, the conversion of lauronitrile was high over the Ni/SiO2, Ni/Al2O3 and Ni/SiAlO with strong surface acidity, but the selectivity to the prime amine was relatively low. The Ni/MgAlO with intermediate strengths of surface acidity and basicity exhibited the high conversion of lauronitrile and high selectivity to the prime amine.

Nanocrystalline ferrites Ni xZn 1− xFe 2O 4: Influence of cation distribution on acidic and gas sensing properties

This work is devoted to a detailed analysis of the interconnection between composition, cation distribution and acidic properties of the surface of nanocrystalline ferrites Ni x Zn 1− x Fe 2O 4 obtained by aerosol pyrolysis. The detailed analysis of the Mössbauer spectra allows us to determine the distribution of cations between tetrahedral and octahedral positions in spinel structure. Depending on samples composition, the tetrahedral positions can be occupied by only Fe 3+ cations (inverse spinel, x≥0.4) or by Fe 3+ and Zn 2+ cations (mixed spinel, x=0, 0.2). Increasing the nickel concentration in the ferrite leads to decrease in the number of strong acid centers on the surface. It was found that the decrease in the contribution of strong surface acid sites leads to an increase in sensory sensitivity of the ferrite towards ammonia. For ethanol detection an inverse relationship between sensor signal and surface acidity was observed.

Microporous carbon molecular sieve as a novel catalyst for the hydroxylation of phenol

A series of microporous carbon-based catalysts were prepared by acidification and/or oxidization treatment of a commercially available carbon molecular sieve (CMS). The resultant samples were characterized by Boehm titration, X-photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), point of zero charge (pH PZC) test, N 2 adsorption, and inductively coupled plasma atomic emission spectrometry (ICP-AES), and employed as catalysts for phenol hydroxylation with H 2O 2. It is found that the acidic functional groups of CMSs play an important role for the catalytic performance. The effects of solvents, reaction temperature, ratio of phenol/catalyst, ratio of phenol/H 2O 2 and reaction time were investigated. Over the sample with the strongest surface acidity among the studied CMSs, the phenol conversion, the selectivity to dihydroxybenzene, and the effective utilization of H 2O 2 reach 29.6%, 85.1% and 80%, respectively under optimal reaction condition. The catalyst is stable in the recycling test. Furthermore, due to its easy physical separation, environmental benignity and low cost, the microporous CMSs is promising for industrial application.

The effect of surface acidic and basic properties on the hydrogenation of aromatic rings over the supported nickel catalysts

Ni/Al 2O 3, Ni/MgAlO and Ni/MgO catalysts containing about 60 wt% of nickel were prepared by the co-precipitation method. The textural and structural properties were characterized and it was found that the dispersion of nickel was high in these catalysts. The active nickel surface area was found to be high (78 m 2/g cat.) in Ni/MgAlO, corresponding to the average nickel particle size of 3.5 nm. Microcalorimetric adsorption of NH 3 and CO 2 showed that the Ni/Al 2O 3 and Ni/MgO exhibited strong surface acidity and basicity, respectively, while the Ni/MgAlO possessed both surface acidity and basicity. In addition, both the initial heat and coverage were higher on Ni/Al 2O 3 than on Ni/MgO for the adsorption of toluene, indicating the strong interaction between the aromatic rings in toluene (that may act as a Lewis base due to the enriched electron densities) and the surface acidic sites on the support. The adsorption of toluene on the metallic nickel surface produced higher heat, indicating the strong interaction of the π electrons in aromatic rings of toluene with the d orbitals of surface nickel atoms. Although the adsorption of H 2 showed the higher active surface nickel area in Ni/MgAlO than in Ni/Al 2O 3, the activities of hydrogenation of toluene and phenol were significantly higher on Ni/Al 2O 3 than on Ni/MgAlO, indicating the important effect of surface acidity on the hydrogenation of aromatic rings.

Preparation of a novel sulfonated carbon catalyst for the etherification of isopentene with methanol to produce tert-amyl methyl ether

Abstract A novel method for the preparation of acid carbon catalyst from glucose and 4-hydroxybenzenesulfonic acid (p-HBSA) was reported. Glucose was first hydrolyzed to hydroxymethylfurfural that reacted with p-HBSA (a phenol compound) to form a phenolic (PF)-like resin containing –SO3H groups. The resin was carbonized and sulfonated further in concentrated sulfuric acid at 443 K to form an amorphous carbon material with a surface area of 22 m2/g. This acidic carbon contained 3.1 mmol/g of strong surface acid sites (–SO3H), and thus exhibited good catalytic activity for the etherification of isopentene with methanol to produce tert-amyl methyl ether.

Preparation and characterization of thermally stable high surface area mesoporous vanadium oxides

Vanadium oxides with high surface areas are desirable for the applications in catalysis and lithium batteries. A new method has been developed in this work for the preparation of mesoporous VO 2 with the surface area of about 180 m 2/g and slit-shaped mesopores. In this simple method, V 2O 5 was first dissolved in aqueous solution of H 2O 2 and the solution was evaporated at 353 K to form a gel with layered structures. After being dried in n-butanol at 353 K, the layered gel intercalated with n-butanol was evacuated at 673 K to form the mesoporous VO 2. Characterizations showed that the prepared mesoporous VO 2 possessed much stronger surface acidity and redox ability than the traditional V 2O 5. Accordingly, it exhibited much higher activity than V 2O 5 for the conversion of isopropanol in air and the selective oxidation of toluene to benzaldehyde and benzoic acid. In addition, the mesoporous VO 2 displayed high thermal stability. It possessed the surface area of 130 m 2/g even after the reaction of selective oxidation of toluene at 633 K.

Michael Reactions Catalyzed by Basic Alkylamines and Dialkylaminopyridine Immobilized on Acidic Silica–Alumina Surfaces

Acid–base bifunctional catalysts were prepared by immobilization of basic amines on acidic silica–alumina (SA) surfaces. Silane-coupling reagents with various amino-functional groups, such as primary, secondary, and tertiary alkylamines, alkyldiamine, and dialkylaminopyridine, were examined as anchoring reagents for the amines in the preparation of catalysts. The obtained immobilized catalysts (SA–NR′R′′) were characterized by solid-state 13C and 29Si MAS NMR and elemental analysis. The catalytic activity of tertiary alkylamines for Michael reactions increased dramatically by the immobilization on silica–alumina, whereas a homogeneous tertiary amine scarcely promoted the reaction. Regarding the kind of amines, the dialkylaminopyridine immobilized silica–alumina with low Al content (SAL) showed the highest catalytic performance among the amine immobilized catalysts. The solid-state 13C NMR analysis revealed the interaction between the nitrogen atom on pyridine ring and a surface strong acid site of the silica–alumina support.

Synthesis of highly active H 2O 2-sensitized sulfated titania nanoparticles with a response to visible light

In this paper, we reported the synthesis of sulfated TiO 2 sensitized with hydrogen peroxide. These prepared TiO 2 showed high photocatalytic activity under the visible light ( λ > 420 nm). X-ray diffraction (XRD), transmission electron micrograph (TEM), UV–vis diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy (FT-IR), BET N 2 adsorption and X-ray photoelectron spectroscopy (XPS) were employed to characterize the properties of the synthesized TiO 2. The results indicated that anatase TiO 2 with strong surface acidity was obtained. The photocatalytic activity of sulfated TiO 2 was compared with that of the commercially available Degussa P25 titanium dioxide by degrading methyl orange (MO) aqueous solutions. The degradation of MO on sulfated TiO 2 under optimal calcining conditions was significantly faster than that on the P25. The active sulfates anchoring on the surface of TiO 2, Ti ions in a tetrahedral coordination and the strong vis absorption may mainly contribute to the high photocatalytic activity of sulfated TiO 2 sensitized with hydrogen peroxide under the visible light.