Weak Basic Sites Research Articles

Ni catalysts supported on nanosheet and nanoplate γ-Al2O3 for carbon dioxide methanation

Abstract Nanosheet (S) and nanoplate (P) γ-Al2O3 were synthesized by simple hydrothermal methods and employed as supports for Ni catalysts in CO2 methanation. Both of the nanostructured Ni/Al2O3 catalysts displayed good activity. In comparison, the Ni/Al2O3-S catalyst showed higher CO2 conversion than the Ni/Al2O3-P counterpart at the reaction temperature ranging from 250 to 400 °C. The physical and chemical properties of the catalysts were systematically characterized by N2 sorption, X-ray diffraction (XRD), high resolution-transmission electron microscopy (HR-TEM), hydrogen temperature-programmed reduction (H2-TPR) and CO2 temperature-programmed desorption (CO2-TPD) techniques. Higher specific surface area and stronger metal-support interactions were confirmed on the Ni/Al2O3-S catalyst, which may lead to smaller particle size of Ni nanoparticles. Moreover, the Ni/Al2O3-S catalyst possessed more abundant weak and medium basic sites, which would benefit the activation of CO2. The smaller Ni size and more suitable basic sites may rationalize the superior activity of the Ni/Al2O3-S catalyst. Besides, the Ni/Al2O3-S catalyst exhibited excellent stability at 325 °C for 40 h.

CuZnAl catalysts prepared by precipitation-hydrothermal method for higher alcohols synthesis from syngas

ABSTRACTCuZnAl catalysts with different Cu/Zn/Al molar ratio prepared by precipitation-hydrothermal method were evaluated for synthesis of higher alcohols from syngas. All the catalysts were characterized by X-ray diffraction (XRD), H2 temperature-programmed reduction (H2-TPR), temperature programmed desorption of ammonia (NH3-TPD-MS) and carbon dioxide (CO2-TPD-MS), and N2 adsorption. These results show that CuZnAl catalysts with hydrotalcite-like structure exhibited optimum performance in terms of both activity and selectivity to higher alcohols. The catalyst with highly dispersed CuO and suitable interaction between Cu with Zn and Al was favorable for synthesis of higher alcohols. Moreover, the synergistic effect between weak acid sites and medium basic sites promoted the chain propagation and oxygenation. When the molar ratio of Cu/Zn/Al was 0.4:0.6:1, the CO conversion could reach 12.5% and the C2+OH selectivity was 13.8%.

Ultrasonic and hydrothermal mediated synthesis routes for functionalized Mg-Al LDH: Comparison study on surface morphology, basic site strength, cyclic sorption efficiency and effectiveness

Amine functionalized layered double hydroxide (LDHs) adsorbents prepared using three different routes: co-precipitation, sono-chemical and ultrasonic-assisted high pressure hydrothermal. The prepared adsorbent samples were characterized using X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning electron microscope-Energy dispersive X-ray spectroscopy (SEM-EDX), Temperature Programmed Desorption (TPD), Brunauer-Emmett-Teller (BET), and Thermogravimetric analysis (TGA), respectively. The performance of the prepared adsorbents was tested in a controlled thermal-swing adsorption process to measure its adsorption capacity, regeneration and cyclic efficiencies subsequently. The characterisation results were compared with those obtained using the conventional preparation routes but taking into account of the impact of sonochemical and hydrothermal pre-treatment on textural properties, adsorption capacity, regeneration and cyclic efficiencies. Textural results depicts a surge in surface area of the adsorbent synthesised by hydrothermal route (311m2/g) from 25 to 171m2/g for conventional and ultrasonic routes respectively. Additionally, it has been revealed from the present study that adsorbents prepared using ultrasonic-assisted hydrothermal route exhibit a better CO2 uptake capacity than that prepared using sonochemical and conventional routes. Thus, the ultrasonic-assisted hydrothermal treatment can effectively promote the adsorption capacity of the adsorbent. This is probably due to the decrease of moderate (M-O) and weak (OH− groups) basic sites with subsequent surge in the number of strong basic sites (O2−) resulting from the hydrothermal process. Moreover, the cyclic adsorption efficiency of the ultrasonic mediated process was found to be 76% compared with 60% for conventional and 53% for hydrothermal routes, respectively. According to the kinetic model analysis, adsorption mechanism is mostly dominated by physisorption before amine modification and by chemisorption after the modification process.

An investigation of iron modified hydroxyapatites used in the activation of n-octane

Iron (9wt.%) modified hydroxyapatites were synthesised using two chemical techniques, namely wet impregnation and co-precipitation. SEM-EDX showed that the material prepared using a wet impregnation technique (9-WET) contained iron distributed on the surface of hydroxyapatite, identified as small particles of Fe2O3, using PXRD and Mössbauer spectroscopy. In contrast, PXRD, Mössbauer spectroscopy and SEM-EDX of the material prepared using a co-precipitation technique (9-COP) revealed that both iron and calcium had been incorporated into the hydroxyapatite structure. The formation of an iron pyrophosphate phase upon reduction of 9-COP was identified using in situ XRD. The material was then oxidised back to form a single phase hydroxyapatite-like material. NH3-TPD showed that the surface of the material prepared by co-precipitation was dominated by both weak acidic and basic sites. The material prepared using the wet impregnation technique, showed a greater degree of reduction. Hydroxyapatite and the iron modified hydroxyapatite materials were tested in the activation of n-octane, using a continuous flow, fixed-bed reactor operated in a down flow mode, and gave a range of octene isomers, aromatic compounds, cracked products and carbon oxides. The product distribution was in agreement with the acid-base properties of the materials. The material prepared using the co-precipitation technique favoured the formation of octene isomers. The conversion of n-octane was in accordance with the reducible nature of the materials. The selectivity toward octene isomers was relatively high over the material prepared using the co-precipitation technique (49 mol% at 550°C), and may have been due to the formation of the iron pyrophosphate phase formed at higher temperatures. The material prepared using the wet impregnation technique showed a maximum selectivity of 27mol% towards octene isomers at 350°C. Selectivity towards carbon oxides was lower over the material prepared using the co-precipitation technique compared to the material prepared using the wet impregnation technique over the entire temperature range tested.

Effect of the acid–base properties of the support on the catalytic activity of ethylene polymerization using supported catalysts composed of Cp2ZrX2 (X = Cl, Me) and Al2O3(F)

Supported catalysts Al2O3/Cp2ZrX2 and Al2O3(F)/Cp2ZrX2 (X = Me, Cl) for the ethylene polymerization were synthesized by anchoring zirconocene on alumina and alumina, modified with 1–7 wt% fluorine (Al2O3(F)). The study revealed that Al2O3(F)/Cp2ZrMe2 catalysts are active in ethylene polymerization in the absence of organoaluminum cocatalyst, whereas Al2O3(F)/Cp2ZrCl2 catalysts are active in the presence of triisobutylaluminum as a co-catalyst. The metallocene complex was strongly anchored on the support. Active component leaching was not observed during polymerization. The acid–base properties of Al2O3(F) were studied by IR spectroscopy of adsorbed probe molecules: CO, pyridine and CDCl3. A maximum activity of the catalysts was observed in the case of the Al2O3(5%F) support, containing Lewis acid sites with absorption bands (νCO) at 2210–2215 cm−1, Bronsted acid sites with a proton affinity (PA) of 1190 kJ/mol, and weak basic sites with PA 850 and 795 kJ/mol. “Cationic-like” complexes formed on the Lewis acid sites with absorption bands at 2180−2200 cm−1 are inactive at ethylene polymerization.

Catalytic Performance of MgO-Supported Co Catalyst for the Liquid Phase Oxidation of Cyclohexane with Molecular Oxygen

A highly-efficient and stable MgO-supported Co (Co/MgO) catalyst was developed for the oxidation of cyclohexane with oxygen. The effects of the Co loading and support on the catalytic activity of the supported Co3O4 catalyst were investigated. The results show that the Co supported on MgO presented excellent activity and stability. When the Co/MgO catalyst with the Co content of 0.2 wt% (0.2%Co/MgO) was used, 12.5% cyclohexane conversion and 74.7% selectivity to cyclohexanone and cyclohexanol (KA oil) were achieved under the reaction conditions of 0.5 MPa O2 and 140 °C for 4 h. After being repeatedly used 10 times, its catalytic activity was hardly changed. Further research showed that the high catalytic performance of the 0.2%Co/MgO catalyst is attributed to its high oxygen-absorbing ability and the high ratio between the amount of weak and medium base sites with the help of the synergistic interaction between Co and MgO.

Dehydration of Glucose to 5-Hydroxymethylfurfural Using LaOCl/Nb2O5 Catalysts in Hot Compressed Water Conditions

The dehydration of fructose and glucose to 5-hydroxymethylfurfural was studied using LaOCl/Nb2O5 in hot compressed water conditions. The catalysts were prepared by impregnation of LaCl3 on Nb2O5 with different loadings. The solids were characterized by EDX, XRD, TGA and N2 physisorption at 77 K and pyridine and CO2 adsorption followed by FTIR; the strength of acidity and basicity was determined by NH3-TPD and CO2-TPD, respectively. The use of acid–base systems for HMF production mainly from glucose requires weak basic sites and moderate acidity condition that is reached with LaOCl/Nb2O5 as was confirmed by acidity and basicity analyses. The presence of Nb2O5 increase HMF yield (>50%) and prevented the formation of undesirable products in hot compressed water conditions, similar results could be obtained with DMSO.

Electrochemical Analysis the influence of Propargyl Methanesulfonate as Electrolyte Additive for Spinel LTO Interface Layer

Propargyl methanesulfonate (PMS) is chosen as an electrolyte additive to study the interfacial performance between the electrolyte and spinel lithium titanate (Li4Ti5O12, LTO) electrode. The result displays that PMS can improve cyclability of Li/LTO cell. Very interestingly, a solid electrolyte interface (SEI) film is formed above 1.0V in the voltage range of 3.0–0V. The observations are explained in terms of PMS include triple-bonded compounds and SO3. The triple-bonded compounds were able to produce a characteristic SEI with dense and low impedance, which can effectively suppress the decomposition of electrolyte, HF generation and LiF formation upon cycling. The SO groups may acts as the weak base site to hinder the reactivity of PF5. Accordingly, the incorporation of PMS into the electrolyte can remarkably enhance the cyclic performance of the Li/LTO cell.

Insight into the Meerwein-Ponndorf-Verley reduction of cinnamaldehyde over MgAl oxides catalysts

The Meerwein-Ponndorf-Verley (MPV) reduction of cinnamaldehyde with 2-propanol to cinnamyl alcohol over MgAl oxide catalysts originated from hydrotalcites was systematically studied. By investigating the influence of calcination temperature and Mg/Al molar ratio on alkaline density and catalytic performance, the relationship between alkaline density and catalytic performance had been established. It was well confirmed that there was an optimal W/M alkaline density ratio for cinnamaldehyde reduction, which lay in the synergetic effect of weak base sites and moderate base sites. In addition, the reaction parameters, reaction pathway, and stability of catalyst were also investigated. Interestingly, the formation of 5-methyl-3-phenylcyclopent-2-en-1-one (1-ONE) was observed for the first time by condensation of cinnamaldehyde and 2-propanol, which was promoted by increasing total alkaline density. And 1-cinnamyl 2-propyl ether (CPE) was detected just under high starting cinnamaldehyde concentration. In the recycling, the used MgAl oxide catalyst exhibited poor activity due to the strong adsorption of organic molecular on active sites, while its reactivity was recovered by calcining simply.

Synthesis of Methyl Acrylate by Aldol Condensation of Methyl Acetate with Formaldehyde Over Al2O3-Supported Barium Catalyst

Vapor phase aldol condensation of methyl acetate with formaldehyde was first studied over Al2O3 with different calcination temperatures and Al2O3-supported barium with different amounts of barium catalysts. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, N2 adsorption–desorption, the pyridine absorption performed via Fourier transform infrared spectroscope, NH3 and CO2 temperature-programmed desorption. The results indicated that the calcination temperature affected the strength and the number of surface acid and base sites over the alumina catalysts. In addition, the moderate Lewis acid and weak base sites were critical to promote this aldol condensation reaction. Adding barium species, which could effectively modified the acid–base properties of Al2O3, clearly improved the catalytic activity and selectivity. The stability and regeneration of the optimum catalyst were also investigated and did not exhibit an obvious decrease in efficiency. Al2O3-supported barium catalyst was found to be an effective catalyst for vapor phase aldol condensation of methyl acetate with formaldehyde as a result of the appropriate intensity of acid and base.

Highly efficient PdAg catalyst using a reducible Mg-Ti mixed oxide for selective hydrogenation of acetylene: Role of acidic and basic sites

A series of reducible Mg-Ti mixed oxides supported PdAg catalysts with tunable acidity/basicity were synthesized for selective acetylene hydrogenation, to investigate the implications of acid-base property on the nature of active component. Catalytic performance of PdAg/MgxTi1−xOy varied with Mg/Ti ratio increasing as volcano curve, which corresponded well with amount of medium acid and weak basic sites. PdAg/Mg0.5Ti0.5Oy exhibited >99% conversion and 83.8% selectivity at 70°C. Enhanced activity was attributed to the promoted hydrogen-spillover effect by moderate acidic sites of Mg0.5Ti0.5Oy support, which facilitated hydrogen activation/dissociation. Preferred selectivity was reasonably owing to the significant geometric effect resulting from high alloying degree of Pd-Ag, which increased the number of Pd linearly coordinated sites, and therefore facilitated the desorption of ethene. Additionally, the increased Pd electronic density caused by the electron transfer from the basic sites and Ti3+ species of Mg0.5Ti0.5Oy support also contributed to the improvement of selectivity.

Ceria and zirconia modified natural clay based nickel catalysts for dry reforming of methane

Ce and Zr promoted Fe/Cu-modified natural clay based catalysts were prepared and tested in dry reforming of methane (DRM) at temperatures from 600 to 800 °C. The physicochemical properties of these catalysts were analyzed by means of N2 adsorption, X-ray diffraction (XRD). H2-temperature programmed reduction (H2-TPR) and CO2-temperature programmed desorption (TPD). Ce and Zr promotion resulted in a considerable increase of the catalytic activity. This increase can be mainly ascribed to an improved reducibility of Ni species, together with slightly higher Ni0 crystal size, that, on the other hand, also catalyze undesired parallel reactions resulting in carbon formation, such as direct methane decomposition. Both Ce and Zr presence also promoted the presence of weak and medium strength basic sites, which are thought to favor CO2 adsorption and desorption on the catalyst surface, leading to enhanced catalytic activity.

Stabilizing interface layer of LiNi0.5Co0.2Mn0.3O2 cathode materials under high voltage using p-toluenesulfonyl isocyanate as film forming additive

Abstract p-Toluenesulfonyl isocyanate (PTSI) is introduced as electrolyte additive in a bid to enhance the electrochemical performances of LiNi0.5Co0.2Mn0.3O2 cathode materials under high voltage. A less resistive and stable film on the cathode surface derived from PTSI oxidation which taken place prior to the carbonate solvents is formed. As a result, the discharge capacity retention of Li/LiNi0.5Co0.2Mn0.3O2 cell is elevated from 71.4% to 86.2% after 100 cycles at room temperature, and from 32.3% to 54.5% after 100 cycles at 55 °C. In addition, the Li/LiNi0.5Co0.2Mn0.3O2 half cell with PTSI exhibits superior rate capability compared to that in baseline electrolyte. The improved performance is not only ascribed to the thin protective layer originated from PTSI decomposition which prevent the successive breakdown of the electrolyte on cathode surface, but it is also attributed to the S O group in PTSI serves as the weak base site to restrain the reactivity of PF5, resulting in the suppression of LiF formation and HF generation.

High-efficiency and low-cost Li/ZnO catalysts for synthesis of glycerol carbonate from glycerol transesterification: The role of Li and ZnO interaction

A series of efficient and low-cost Li/ZnO catalysts were prepared by a simple impregnation method and investigated for the synthesis of glycerol carbonate (GC) from the transesterification of glycerol with dimethyl carbonate (DMC). The Li/ZnO catalysts were characterized using XRD, SEM, FT-IR, TG-DSC, TPD and XPS. It was found that the basicity of the catalysts highly depended on the Li loading and calcination temperature. The weak and moderate basic sites on the catalyst surfaces originated from the ZnO and Li+ interaction. The strong basic sites were attributed to the substitution of Zn2+ by Li+ in the ZnO lattice, which led to straining of Zn-O bonds and the formation of [Li+ O−] species. It was the strong basic sites rather than the weak and moderate basic sites that catalyzed the transesterification of glycerol with DMC. The highest catalytic activity was observed over the ZnO loaded with 1wt.% LiNO3 and calcined at 500°C. Glycerol conversion of 97.40% and GC yield of 95.84% were obtained over this catalyst at 95°C in 4h.

Hydrogenation of CO2 to synthetic natural gas over supported nickel catalyst: effect of support on methane selectivity

Nickel-based catalysts were prepared by co-precipitation method and applied for the CO2 conversion to synthetic natural gas. Two batches of catalysts were prepared with the different amount of Ni and were characterized by various techniques such as XRD, TPD, TPR, XPS, and TEM. Catalytic activity was studied under atmospheric pressure, a temperature of 350 °C, GHSV of 2000 h−1 and N2:CO2:H2 = 4:1:4. Highest CO2 conversion achieved was 70 with 99 % selectivity to methane. The activity of catalysts depends on the nickel content and nickel dispersion. Selectivity to methane depends inversely on the concentration of weak and moderate strength basic sites. Comparable quantity of basic sites present over catalysts, the methane selectivity is observed to be similar but the CO2 conversion changed due to change in Ni content. Catalysts having equal amounts of Ni exhibited increase in CH4 selectivity with the decrease in basic sites.

HaldorTopsoe: increased profitability in 1H 2016

In general, there are three processes for production of synthesis gas; steam reforming, CO2 reforming and partial oxidation of methane or natural gas. In the present work, we refer to tri-reforming of methane to synthesize syngas with desirable H2/CO ratios by simultaneous oxy-CO2-steam reforming of methane. In this study, we report the results obtained on tri-reforming of methane over the Ni/ZrO2 based catalyst in order to restrain the carbon deposition and to evaluate the catalytic performance. Results of tri-reforming of CH4 by three catalysts (Ni/Ce–ZrO2, Ni/ZrO2 and Haldor Topsoe R67-7H) are showed that the coke on the reactor wall and the surface of catalyst were reduced dramatically. It was found that the weak acidic site, basic site and redox ability of Ce–ZrO2 play an important role in tri-reforming of methane conversion. Carbon deposition depends not only on the nature of support, but also on the oxidant as like steam or oxygen. Therefore, the process optimization by reactant ratios is important to manufacture the synthesis gas from natural gas and carbon dioxide.

Determination of basic sites in Mg–Al mixed oxides by combination of TPD-CO2 and CO2 adsorption calorimetry

We present the critical analysis of the utilization of CO2 adsorption calorimetry/volumetry and TPD-CO2 for the determination of the Mg–Al mixed oxide basicity. The aim of work is the description and the evaluation of both methods with respect to the fact when the same types of CO2 adsorption complexes are involved. Critical parts of basic sites determination are originally discussed for both methods. In TPD-CO2, the process of the purging of non-specifically physisorbed CO2 is stressed. In CO2 adsorption calorimetry, the differential heat of CO2 distinguishing CO2 adsorption on weak basic sites and non-specific CO2 physisorption is stressed. Both methods are applied on series of selected Mg/Al mixed oxides varying in Mg/Al molar ratio and alkali co-cation. We show that the generally used TPD-CO2 does not provide complete information about basic sites since some weak sites form unstable CO2 species and these species could not be involved in TPD experiments. All our TPD-CO2 experiments reflect at 0–485 °C those CO2 adsorbed in the range of the differential heat of CO2 above 30–32 kJ mol−1.

Selective synthesis of acetone from isopropyl alcohol over active and stable CuO–NiO nanocomposites at relatively low-temperature

CuO–NiO nanocomposite catalysts were synthesized by an oxalate precipitation route. The basicity of the catalysts was measured using adsorption–desorption of acetic acid. The catalytic conversion of isopropanol to acetone was carried out in a conventional fixed bed flow type reactor at 200 °C using N2 as a carrier gas. The results indicated that, the addition of NiO to CuO greatly enhanced the electrical conductivity via the creation of new charge carriers (Cu+–Ni3+). In addition, the results revealed that the catalyst containing 30 wt.% NiO calcined at 400 °C possesses the highest catalytic activity with 98% conversion and 100% selectivity to acetone. The remarkable catalytic performance of the synthesized catalysts is attributed to the decrease of the energy gap, the increase in the concentration of charge carries (Cu+–Ni3+), and to the creation of more weak and intermediate basic sites.

Enhancement effects of ultrasound assisted in the synthesis of NiAl hydrotalcite for carbonyl sulfide removal

Ultrasonic effect in the synthesis of catalysts of NiAl oxides prepared starting from the coprecipitation method of a hydrotalcite structure was evaluated in this work. Removal of carbonyl sulfide (COS) at low temperature over the hydrotalcite-derived oxides was studied. The samples were characterized by X-ray Diffraction (XRD), scanning electron microscope (SEM), N2 adsorption/desorption techniques, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and CO2 temperature-programmed desorption (TPD). It is found that hydrotalcite treated with ultrasonic has smaller average crystallite size and higher particle dispersion compared to hydrotalcite without ultrasonic treatment. As a result, mixed oxides derived from hydrotalcite treated with ultrasonic show more developed pore structure which is good for the physical adsorption of gaseous pollutant. The result of desulfuration test showed that removal efficiency of COS on the NiAl mixed oxides prepared by ultrasonic method (30min) is greater than that on the catalyst prepared without the ultrasonic irradiation assistance with the same aging time. One important reason for the high activity is that when the ultrasonic is used the number of weak basic sites (OH− groups) and moderate basic sites (M–O) was increased, whereas the number of strong basic sites (O2−) was decreased. Therefore, ultrasonic treatment promoted the COS hydrolysis and suppress the poisoning of the catalyst.

Low temperature dry methane reforming over Ce, Zr and CeZr promoted Ni–Mg–Al hydrotalcite-derived catalysts

Hydrotalcite derived catalysts promoted with Ce, Zr and CeZr showed considerable activity in dry methane reforming (DMR) at low temperatures (550 °C). Direct methane decomposition resulting in the extensive formation of fishbone-type carbon nanofibers was substantially inhibited in the presence of Zr. Physicochemical characterization by means of N2 adsorption, XRD, TPR and CO2-TPD evidenced narrower porosity and higher surface areas for the Zr-containing catalysts, together with the presence of smaller Ni particles (around 4 nm) and CO2 preferential adsorption in weak basic sites. Such small Ni particles are inactive towards the direct methane decomposition reaction. The ability of the Zr-containing catalysts to adsorb CO2 on weak basic sites results in the formation of active carbonate species that are able to react with methane through the DMR route. The reverse Boudouard reaction occurs simultaneously to a certain extent in the presence of Zr-promoted catalyst, since carbon nanotube formations were visible on the catalyst surface upon its utilization.