Zr Catalysts Research Articles

High N2 selectivity in selective catalytic reduction of NO with NH3 over Mn/Ti-Zr catalysts.

A series of Mn-based catalysts were prepared by a wet impregnation method for the selective catalytic reduction (SCR) of NO with NH3. The Mn/Ti–Zr catalyst had more surface area, Lewis acid sites, and Mn4+ on its surface, and showed excellent activity and high N2 selectivity in a wide temperature range. NH3 and NO oxidation was investigated to gain insight into NO reduction and N2O formation. The formation of N2O was primarily dominated by the reaction of NO with NH3 in the presence of O2via the Eley–Rideal mechanism. An intimate synergistic effect existed between the Mn-based and the Ti–Zr support. It was demonstrated that the Ti–Zr support greatly promoted the catalytic performance of Mn-based catalysts.

New olefin block copolymers of ethylene/1-hexene synthesized by iron and zirconocene catalysts in the presence of ZnEt2

Development of olefin block copolymers (OBCs) based on new catalytic systems is challenging. We evaluate the performance of rac-ethylenebis(1-η 5-indenyl)zirconium dichloride (Zr) and bis(imino)pyridine iron (Fe) catalysts, with different comonomer affinities, in copolymerization of ethylene/1-hexene. In-depth investigation of thermal properties reveals that chain shuttling agent (CSA) has diverse effects on the microstructure formed by the individual catalysts. Specifically, as confirmed by CNMR measurements, the comonomer affinity of the Zr catalyst is noticeably reduced while it remains unchanged for the Fe catalyst. Copolymers produced by the binary catalytic system in the presence of CSA do not show indications for formation of blocky structure at higher Zr fractions, while at lower fractions, a significantly different behavior is exposed, e.g., high melting temperature peak is replaced by broad low-temperature endotherm and lower molar mass with narrow distribution is obtained. It could be concluded that this catalyst composition can be a good candidate for operative production of OBCs.

Effect of Cs-Ce-Zr Catalysts/Soot Contact Conditions on Diesel Soot Oxidation.

Cs–Ce–Zr catalysts with various weight ratios are prepared by the sol–gel method in this paper. The main crystalline phases were identified by X-ray diffraction. The activities of catalysts during soot combustion were tested by thermogravimetric and differential scanning calorimetry. The contact conditions of soot/catalysts (sintered at 450 and 380 °C, respectively, under loose and tight contact conditions) were observed by scanning electron microscopy to study the effect of contact conditions on catalytic activity, and it was determined that the catalytic activities under tight contact conditions are superior to those under loose contact conditions. However, the soot oxidation rate speeds up after the peak temperature of about 450 °C under loose contact conditions, which is due to the fact that the contact condition is enhanced by melting CsNO3. The soot onset ignition temperature is lower for the catalysts with more Cs content under loose contact conditions. The minimum gaps of the soot onset ignition temperature and soot oxidation rates under the two contact conditions are 32 and 7 °C, which shows that the gap of catalytic activities under the respective contact conditions can be decreased by the formation of different crystalline phases.

Transformation of Metal–Organic Framework Secondary Building Units into Hexanuclear Zr-Alkyl Catalysts for Ethylene Polymerization

We report the stepwise and quantitative transformation of the Zr6(μ3-O)4(μ3-OH)4(HCO2)6 nodes in Zr-BTC (MOF-808) to the [Zr6(μ3-O)4(μ3-OH)4Cl12]6- nodes in ZrCl2-BTC, and then to the organometallic [Zr6(μ3-O)4(μ3-OLi)4R12]6- nodes in ZrR2-BTC (R = CH2SiMe3 or Me). Activation of ZrCl2-BTC with MMAO-12 generates ZrMe-BTC, which is an efficient catalyst for ethylene polymerization. ZrMe-BTC displays unusual electronic and steric properties compared to homogeneous Zr catalysts, possesses multimetallic active sites, and produces high-molecular-weight linear polyethylene. Metal-organic framework nodes can thus be directly transformed into novel single-site solid organometallic catalysts without homogeneous analogs for polymerization reactions.

Stereoregular Brush Polymers and Graft Copolymers by Chiral Zirconocene-Mediated Coordination Polymerization of P3HT Macromers.

Two poly(3-hexylthiophene) (P3HT) macromers containing a donor polymer with a polymerizable methacrylate (MA) end group, P3HT-CH2-MA and P3HT-(CH2)2-MA, have been synthesized, and P3HT-(CH2)2-MA has been successfully homopolymerized and copolymerized with methyl methacrylate (MMA) into stereoregular brush polymers and graft copolymers, respectively, using chiral ansa-zirconocene catalysts. Macromer P3HT-CH2-MA is too sterically hindered to polymerize by the current Zr catalysts, but macromer P3HT-(CH2)2-MA is readily polymerizable via either homopolymerization or copolymerization with MMA in a stereospecific fashion with both C2-ligated zirconocenium catalyst 1 and Cs-ligated zirconocenium catalyst 2. Thus, highly isotactic (with mm% ≥ 92%) and syndiotactic (with rr% ≥ 93%) brush polymers, it-PMA-g-P3HT and st-PMA-g-P3HT, as well as well-defined stereoregular graft copolymers with different grafted P3HT densities, it-P(M)MA-g-P3HT and st-P(M)MA-g-P3HT, have been synthesized using this controlled coordination-addition polymerization system under ambient conditions. These stereoregular brush polymers and graft copolymers exhibit both thermal (glass and melting) transitions with Tg and Tm values corresponding to transitions within the stereoregular P(M)MA and crystalline P3HT domains. Acceptor molecules such as C60 can be effectively encapsulated inside the helical cavity of st-P(M)MA-g-P3HT to form a unique supramolecular helical crystalline complex, thus offering a novel strategy to control the donor/acceptor solar cell domain morphology.

CO2 hydrogenation to methanol over Cu/Zn/Al/Zr catalysts prepared by liquid reduction

Cu/Zn/Al/Zr catalysts containing Cu in three valence states (Cu2+, Cu+ and Cu0) were prepared using a liquid reduction method and subsequently calcined at different temperatures. The effects of the calcination temperature on the catalyst structure, interactions among components, reducibility and dispersion of Cu species, surface properties and exposed Cu surface area were systematically investigated. These materials were also applied to the synthesis of methanol via the hydrogenation of CO2. The results show that a large exposed Cu surface area promotes catalytic CO2 conversion and that there is a close correlation between the Cu+/Cu0 ratio and the selectivity for methanol. A calcination temperature of 573 K was found to produce a Cu/Zn/Al/Zr catalyst exhibiting the maximum activity during the synthesis of methanol.

Methanation of Carbon Dioxide over Ni–Ce–Zr Oxides Prepared by One-Pot Hydrolysis of Metal Nitrates with Ammonium Carbonate

Ni–Ce–Zr mixed oxides were prepared through one-pot hydrolysis of mixed metal nitrates with ammonium carbonate for CO2 methanation. The effects of Ce/Zr molar ratio and Ni content on catalysts’ physical and chemical properties, reduction degree of Ni2+, and catalytic properties were systematically investigated. The results showed that Zr could lower metallic Ni particle sizes and alter interaction between Ni and supports, resulting in enhancements in the catalytic activity for CO2 methanation. The Ni–Ce–Zr catalyst containing 40 wt % Ni and Ce/Zr molar ratio of 9:1 exhibited the optimal catalytic properties, with 96.2% CO2 conversion and almost 100% CH4 selectivity at a low temperature of 275 °C. During the tested period of 500 h, CO2 conversion and CH4 selectivity over Ni–Ce–Zr catalyst kept constant under 300 °C.

A Study on the Order of Calcination and Liquid Reduction over Cu-Based Catalyst for Synthesis of Methanol from CO2/H2

Cu/Zn/Al/Zr catalysts were prepared by liquid reduction method and tested for the synthesis of methanol by CO2 hydrogenation. With the purpose of relieving the aggregation of reduced Cu species, the order of calcination and liquid reduction process was modified. Catalysts with different thermal treatments were characterized by XRD, N2 physisorption, TEM, N2O chemisorption, TG–MS, XPS, TPR, CO2-TPD techniques. When liquid reduction was performed after calcination procedure, metallic Cu specific area and dispersion increased and the interaction among components was strengthened. The modified catalyst displays a slight superiority in CO2 conversion and methanol selectivity.

Catalytic cracking of sunflower oil under Zr catalysts using thermogravimetry

Catalytic cracking of vegetable oils is an alternative method for the production of biofuels. The use of catalysts such as MCM-41 with zirconium results in the presence of acid sites that favor the cracking reactions, where their catalytic activity can be evaluated by thermogravimetric analysis. The present work aimed to prepare and determine the physicochemical properties of a catalyst based on MCM-41 incorporated with different percentages of zirconium. The materials were characterized by X-ray diffraction, adsorption and desorption of N2, energy-dispersive X-ray, scanning electron microscopy, thermogravimetry (TG) and differential thermogravimetry (DTG). In addition, their catalytic behavior has been evaluated in the catalytic cracking of sunflower oil, through the TG/DTG/DSC thermal analysis techniques. The amount of the zirconium oxide incorporated into MCM-41 support has not destroyed the typical structure of MCM-41, and the insertion promoted a change to the pore diameter and pore volume, indicating the presence of oxide inside the pores and on the external area. All catalysts developed activity in sunflower oil cracking, even at low percentage of ZrO2, especially the Zr2-MCM-41 sample, which obtained more efficiency. Thus, all catalysts are promising for use in cracking, and thermogravimetric analysis has been proved effective for monitoring the catalytic activity.

Development of cylindrical laminated methanol steam reforming microreactor with cascading metal foams as catalyst support

In this study, the cascading metal foams were used as catalyst supports for constructing a new type of cylindrical laminated methanol steam reforming microreactor for hydrogen production. The two-layer impregnation method was used to load the Cu/Zn/Al/Zr catalysts, and the ultrasonic vibration method was then employed to investigate the loading performance of metal foams with different types and thicknesses. Furthermore, the effect of the type of catalyst placement, pores per inch (PPI) and foam type on the performance of methanol steam reforming microreactor was studied by varying the gas hourly space velocity (GHSV) and reaction temperature. Compared with two other types of catalyst placement studied, the microreactor containing catalyst-loaded metal foams without clearance cascading (3×2) showed the highest hydrogen production performance. When the PPI of the metal foam was increased from 50 to 100, both the methanol conversion and the H2 flow rate gradually increased. Our results also showed that a microreactor with Cu foam as a catalyst support exhibits increased hydrogen production and higher stability than those of a microreactor with Ni foam.

Quantitative Comparative Kinetics of 1-Hexene Polymerization across Group IV Bis-Phenolate Catalysts

The kinetics of 1-hexene polymerization using a series of three Ti amine bis-phenolate catalysts, Ti[tBu-ONXO]Bn2 (X = THF (1), pyridine (2), NMe2 (3)), were investigated and compared to analogous Zr and Hf complexes. A model-based approach using a diverse set of data (including monomer consumption, molecular weight evolution, etc.) was employed to determine the reaction specific rate constants of the simplest mechanism. These catalysts exhibited similar mechanisms that include the elementary reaction steps of initiation, propagation via 1,2-insertion, misinsertion via 2,1-insertion, recovery from misinsertion by 1,2-insertion, and monomer independent chain transfer. Rate constants of the Ti catalysts are typically lower than those of the Hf and the Zr catalysts by 1 and 2 orders of magnitude, respectively. The percentage of regioerrors follows the trend of Ti > Hf > Zr for catalyst 1 while the trend of Ti > Zr > Hf occurs for catalysts 2 and 3. The ratio of the propagation rate to the termination rate at...

N-Alkylation of Alkylolamines with Alcohols Over Mesoporous Solid Acid–Base Cs–B–Zr Catalyst

The mesoporous solid acid–base Cs–B–Zr mixed oxides were synthesized using the co-precipitation method followed by a subsequent thermal treatment. The catalytic activity of solid Cs–B–Zr mixed oxide was tested for solvent free acid–base catalysed direct alkylolamines with alcohols as green alkylating agent. The effects of Cs/B/Zr ratio, calcination temperature, reaction conditions, and reaction substrate on the catalytic performance of the catalysts were investigated. The XRD, N2 adsorption–desorption, ICP-OES, FT-IR and NH3/CO2-TPD results showed that the mesoporous structure and acid–base properties of the catalysts play important roles in the reaction. A suitable number of acid and basic sites on the catalyst lead to a high activity for the N-alkylation reaction. A direct N-alkylation of amino alcohol with alcohols has been developed using mixed oxide Cs–B–Zr as an acid–base bifunctionalized catalyst.

Higher alcohols synthesis via CO hydrogenation on Cu/Zn/Al/Zr catalysts without alkalis and F–T elements

A series of Cu/Zn/Al/Zr catalysts without alkalis and F–T elements, were prepared with various atomic ratios of Al/Zr by complete liquid-phase technology and tested for higher alcohols synthesis from CO hydrogenation. The results showed that the Cu/Zn/Al catalyst exhibited excellent higher alcohols selectivity, reaching approximately 58.8%. With the increase of Zr/Al atomic ratio, the catalytic activity and stability increased, but methanol became the dominant product in the liquid products over Cu/Zn/Zr catalyst. It was concluded that Al favored the formation of higher alcohols and Zr was beneficial to improve the stability of catalysts. Characterization results showed that the addition of Zr improved the dispersion of Cu and made the catalyst easier to be reduced. It also favored the stability of pore structure and decreased the amount of weak acidic sites. It was also found that the amount of the weak acidic sites played a key role in the higher alcohols formation and the amount of weak acidic sites decrease might lead to the deactivation of catalysts.

Hydrothermal preparation of Fe–Zr catalysts for the direct conversion of syngas to light olefins

Two-step hydrothermal preparation of Fe/Zr–K catalysts could improve the olefin selectivity and product distribution by reducing the secondary hydrogenation ability and suppressing the formation of heavy hydrocarbons during CO hydrogenation.

Hydrogenation of CO2 to dimethyl ether on La-, Ce-modified Cu-Fe/HZSM-5 catalysts

Cu–Fe–La/HZSM-5 and Cu–Fe–Ce/HZSM-5 bifunctional catalysts were prepared and applied for the direct synthesis of dimethyl ether (DME) from CO2 and H2. The catalysts were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, H2-temperature programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS). The results showed that La and Ce significantly decreased the outer-shell electron density of Cu and improved the reduction ability of the Cu–Fe catalyst in comparison to the Cu–Fe–Zr catalyst, which may increase the selectivity for DME. The Cu–Fe–Ce catalyst had a greater specific surface area than the Cu–Fe–La catalyst. This promoted CuO dispersion and decreased CuO crystallite size, which increased both the DME selectivity and the CO2 conversion. The catalysts were stable for 15h.

ChemInform Abstract: Degradation Performance of a Keggin Type Zn—Mo—Zr Catalyst for Acidic Green B with Ultrasonic Waves.

AbstractNa6[Zn(Mo11ZrO39)]·20H2O with a Keggin structure of the 1:1:11 series is prepared by the classic acidification method using an aqueous Na2MoO4 solution at pH 6.5 to which aq.

Facile Oxidative Desulfurisation of Benzothiophene Using Polyoxometalate H4[α-SiW12O40]/Zr Catalyst

A highly active catalyst H4[α-SiW12O40]/Zr based polyoxometalete Keggin type was prepared by wet impregnation method and was characterized by FTIR spectroscopy, X-ray diffractometer, surface textural property by SEM, and analysis of porosity by BET method. H4[α-SiW12O40]/Zr was successfully synthesized and showed uniform properties with block solid structure which was applied as heterogeneous stable catalyst for oxidative desulfurization of benzothiophene under simple and mild condition using H2O2 as oxidant. Facile conversion of benzothiophene to sulfone by using heterogeneus H4[α-SiW12O40]/Zr catalyst up to 99% was observed to show the active catalytically. Keggin H4[α-SiW12O40]/Zr cage structure after reaction was different from fresh catalyst which was indicated by the instability of H4[α-SiW12O40]/Zr under reaction condition. © 2015 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0)

Isotopic study of the rates of hydrogen provision vs. methanol synthesis from CO2 over Cu–Ga–Zr catalysts

Cu/ZrO2 and Ga2O3-promoted Cu/ZrO2, with the same copper loading (2.6wt.%), were evaluated in a Carberry-type batch-operated microreactor for methanol synthesis using a H2/CO2/He mixture (75/22/3v/v) at 1.6MPa and 498K. The gallia-promoted catalyst was 5-fold more active to methanol production (per catalyst specific surface) than Cu/ZrO2. In addition, after the incorporation of Ga2O3 the selectivity to the alcohol was enhanced by a factor of three.To discern whether different degrees of hydrogen provision were responsible for the dissimilar performances observed, thus affecting the overall reaction rate to methanol (RCH3OH), the ability to activate H2 of the catalysts was assessed – in the same microreactor – by a combination of H2/D2 isotopic equilibration (H2/D2/Ar=37.5/37.5/25v/v) and H/D isotopic exchange (D2/Ar=10/90v/v) reactions at 0.1MPa, between 353 and 393K.The equilibration rate (Requil) was far higher than RCH3OH on both, Cu/ZrO2 and Ga2O3-promoted Cu/ZrO2. In agreement with the property of gallia to dissociate H2, Ga2O3 increased further Requil in the ternary catalyst. Vis-à-vis, the isotopic-exchange reaction rates (Rexchg) were considerably lower than the Requil for each catalyst, more so for the gallium containing one. However, the extrapolation of those Rexchg values to the temperature of methanol synthesis gave always much higher rates than RCH3OH, thus allowing to conclude that the supply of ‘active’ hydrogen is fully secured on these copper-supported (gallium-promoted) catalysts.

Acidity and catalytic performance of Yb-doped [formula omitted]/Zr in comparison with [formula omitted]/Zr catalysts synthesized via different preparatory conditions for biodiesel production

Highly efficient, robust and mesoporous sulfated zirconia, SZ catalysts were prepared by co-precipitation and incipient-wetness routes with sufficient and in-excess acid. The study investigated the effect of pH, precursor type, and concentration, on SZ and compared their acidity and performance with ytterbium-doped SZ toward transesterification. N2 sorption, elemental analysis, XRD, and ammonia temperature-programmed desorption (NH3-TPD) revealed the properties of the catalytic materials. The specific surface area increases independently of the presence of Ti up to 60.33 m2/g, with increasing pH while pore size of the tetragonal crystallites decreases from 37.04 to 6.83 nm. Soaking the material in sufficient 0.5-M H2SO4 produced 37.04 nm SBET in contrast to 21.21 nm from soaking in excess. Double sulfation ensured sulfate incorporation while moderate precursor amounts enhanced activity of the materials. Interestingly, despite low specific surface area, which was due to short aging period, large mesoporosity, high amount, and dispersion of active sites on Yb-doped SZ, SZr-Ti-Yb-500-4/s ensured remarkable activity. The catalyst converted ca. 99% of used frying oil containing ca. 48 wt. % FFA. Consequently, this highlights the prospect of producing biodiesel at lower cost especially with current dwindling price of crude oil.

Selective catalytic oxidation of H2S to elemental sulfur over titanium based Ti–Fe, Ti–Cr and Ti–Zr catalysts

In this study, titanium oxide catalyst was incorporated with iron, chromium and zirconium to improve catalytic activity for selective catalytic oxidation of H2S to elemental sulfur. Equimolar titanium based iron (Ti–Fe), chromium (Ti–Cr) and zirconium (Ti–Zr) catalysts were synthesized by the complexation method and tested in oxidation between the temperature range of 200–300 °C and using different O2/H2S ratios. Ti–Fe catalyst with Fe2TiO5 crystalline phase and Ti–Cr catalyst with mainly Cr2O3 crystalline phase showed complete conversion of H2S and high sulfur selectivity (close to one) at 250 °C. Ti–Zr catalyst having relatively high surface and small pore diameter could not prevent sulfur deposition on the surface and lost in catalytic activity at the same temperature. Ti–Fe catalyst had high activity with 100% conversion and sulfur selectivity in the reaction period of an experimental run (150 min) even at lower oxidation temperature (200 °C). It was concluded that incorporation of iron into Ti–Fe catalyst structure improved the redox ability and surface acidity of the catalyst. Fe2TiO5 mixed metal oxide in the Ti–Fe catalyst was responsible and active phase resulting in complete conversion of H2S and high sulfur selectivity in the selective oxidation of H2S to elemental sulfur.