Zr Catalysts Research Articles

Effects of promoters on methane dry reforming over Ni catalyst on a mixed (a-Al2O3+TiO2-P25) support

Carbon dioxide reforming of methane to synthesis gas over Ni on a mixed (α-Al2O3 and TiO2-P25) support was investigated. The effect of adding Zr and Ce promoters to the supported catalyst was studied. Catalytic testes were performed at atmospheric pressure, flow rate of 33 ml/min and various reaction temperatures in the range of 500 and 800°C. The influence of several operating conditions such as feed ratio, space velocity and oxygen addition (that is, combined dry reforming and partial oxidation) on catalyst activity, stability and synthesis gas ratio (H2/CO) were studied. Spent and fresh catalysts were characterized by scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) techniques. The lowest carbon formation on the catalyst was attained at 800°C. Zr gave highest promotion and best stability. For the 1%Ni+0.15%Zr catalyst over 80% a- Al2O3+20% TiO2 support, the best conversions of CH4 and CO2 were 97 and 89.5%, respectively at 800°C and CO2/CH4 = 1.3. Key words: CO2 reforming, CH4, supported catalysts, coke, promoter, stability, partial oxidation.

Zirconium‐Catalyzed Intermolecular Hydroamination of Alkynes with Primary Amines

AbstractA simple catalyst system generated in situ by combination of 5 mol‐% [Zr(NMe2)4] and 10 mol‐% of a sulfonamide catalyzes the intermolecular hydroamination of alkynes with primary amines. At elevated temperatures, hydroamination is achieved with both internal and terminal alkynes as well as with sterically demanding and less demanding primary amines. In contrast, secondary amines do not react under identical conditions. Of the sulfonamide additives investigated, sterically demanding tosylamides such as N‐(tert‐butyl)‐p‐toluenesulfonamide give the best results. The regioselectivity of the addition of amine to unsymmetrically substituted internal as well as terminal alkynes is significantly influenced by the nature of the sulfonamide additive. In particular, the successful use of sterically less demanding primary amines such as n‐hexyl‐ or benzylamine clearly indicates that the assumption that Zr catalysts generally form catalytically inactive bridging μ2‐imido dimers or other unreactive intermediates in the presence of these amines is not correct.

Fabrication and characteristics of cube-post microreactors for methanol steam reforming

The lamination-plate structure patterned with microchannels and triangle manifolds regarded as one of the preferred constructions for micro fuel reformers. Learned from the microchannel plate structure, a similar plate structure with cube-post array and triangle manifolds is proposed in this work. A micro-milling process is applied to fabricate the cube posts on the plate surface, and the influences of cutting parameters on the burr formation are analyzed. Experimental results indicate that larger cutting speed, smaller feed rate and cutting depth are in favor of obtaining relatively small burrs. Two plates with different cube-post dimensions and manifold structures are experimentally investigated the performances of methanol steam reforming over the Cu/Zn/Al/Zr catalyst. It indicates that the reactor with small-scale cube posts and acute triangle manifold presents better reforming performances at 260 °C than that of the one with large-scale cube posts and right triangle manifolds. However, their performances are closed to each other at relatively high reaction temperature since the catalyst activity is situated in dominated position at the time.

Cyclohexane Oxidation Catalyzed by Au/MxOyAl<sub>2</sub>O<sub>3</sub> Using Molecular Oxygen

Alumina was modified by doping with metal oxide and then used as the support for depositing gold by an impregnation-ammonia washing method to obtain Au/MxOy/Al2O3(M=Co, Zr and Ce) catalysts. These samples were characterized by inductively coupled plasma-atomic emission spectrometry (ICP-AES), transmission electron microscope (TEM) and X-ray diffraction (XRD). The effects of Co3O4content, metal oxide and mixed metal oxides on the catalytic activity for the selective oxidation of cyclohexane to cyclohexanone and cyclohexanol using molecular oxygen as oxidant were studied. The results showed that better catalytic performance was obtained over Au/MxOy/Al2O3catalysts compared with over Au/Al2O3catalysts. 9.69% conversion of cyclohexane and 93.31% selectivity to cyclohexanone, cyclohexanol and cyclohexyl hydroperoxide, with 1.02 ratio of cyclohexanone to cyclohexanol were obtained over the Au/MxOy/Al2O3catalyst at 150 , 1.5 MPa for 3 h. Moreover, according to the recycling test, the catalyst could be reused four times without remarkable loss of activity.

Oriented linear cutting fiber sintered felt as an innovative catalyst support for methanol steam reforming

A kind of oriented linear cutting fiber sintered felt as an innovative catalyst support for methanol steam reforming was proposed. Multiple long copper fibers fabricated by cutting method were arranged in parallel and then sintered together in a mold pressing equipment under the condition of high temperature and protective gas atmosphere. The characteristics of oriented linear cutting fiber sintered felt coated with Cu/Zn/Al/Zr catalyst for methanol steam reforming were experimental investigated under different GHSVs and reaction temperatures. Results indicated that the structure of sintered felt was the key influencing factor for the reaction performances on the condition of low GHSV or reaction temperature whereas the structure of sintered felt showed little influences with high GHSV or reaction temperature. By the analysis of SEM image and ultrasonic vibration testing method, it was found that the coarse surface pattern of cutting fiber could effectively enhance the adhesion intensity between the catalyst and the copper fibers, as well as present relatively large specific surface area in the microchannels. And hence the oriented linear cutting fiber sintered felt present better performances of methanol steam reforming than the oriented linear copper wire sintered felt on the condition of low GHSV or reaction temperature.

ChemInform Abstract: Discovery of ZACA Reaction : Zr‐Catalyzed Asymmetric Carboalumination of Alkenes

AbstractReview: 94 refs.

One-step production of biodiesel from Nannochloropsis sp. on solid base Mg–Zr catalyst

Nannochloropsis sp., one kind of green microalgae cultivated autotrophically and axenically in laboratory, is used as raw material to produce biodiesel by one-step method in an amended reactor. The effects of several reaction parameters on transesterification over Mg–Zr solid base catalyst were investigated through both conventional method and one-step method. One-step method could give a higher yield of methyl ester than conventional two-step method, which demonstrates that the present one-step method is suitable for biodiesel production from the microalgae Nannochloropsis sp. Moreover, the present one-step method realizes the convenient in situ separation of catalyst from microalgae residue which can be easily used consequently, reducing the procedure units as well as the overall costs.

Discovery of ZACA reaction − Zr-catalyzed asymmetric carboalumination of alkenes

A single-stage, i.e., degree of polymerization of one, and enantioselective version of the ZieglerNatta alkene polymerization was envisioned as a potentially significant and useful method for catalytic asymmetric C–C bond formation, shortly after the corresponding alkyne version involving Zr-catalyzed alkylalumination of alkynes was discovered in 1978. However, the discovery of such an asymmetric reaction proved to be a major challenge. At least three widely observable unwanted side reactions, i.e., (1) cyclic carbometalation, (2) β-H transfer hydrometalation, and (3) alkene polymerization, represented by the Ziegler-Natta polymerization, were noted and were to be avoided. With Zr as the metal at the catalytic center, we eventually came up with a notion that di- or multiple alkylation of Zr was to be avoided for achieving superior acyclic asymmetric carbometalation. This, in turn, led us to avoid the use of highly nucleophilic alkylmetals containing alkali metals and Mg. Aluminum used in ZieglerNatta polymerization that can selectively monoalkylate Zr proved to be one of a very limited number of favorable metals. Even so, undesirable cyclic carbozirconation can occur in nonpolar solvents via intricate bimetallic routes to cyclic organozirconium species. The vastly different reactant-catalyst stoichiometry and the absence of polymerization promotors, such as methylaluminoxane, in our investigations permit us to ignore the Ziegler-Natta polymerization as a serious and unwanted side reaction, although use of limited amounts of promotors can in some cases accelerate otherwise sluggish ZACA reactions. Selection of the currently used Zr catalysts including (R)- and (S)-(NMI)2ZrCl2, dichlorobis(neomenthylindenyl)zirconium was made by screening 15 or so known chiral zirconocene derivatives. Systematic scientific design and screening of chiral ligands are clearly highly desirable, and efforts along this line are ongoing. Even at the current level of development, however, the ZACA reaction shows considerable promise as an efficient and selective method for catalytic asymmetric C–C bond formation, which has already been used to significantly modernize and improve syntheses of natural products including deoxypolypropionates and isoprenoids of biological and medicinal interest.

New insights into the performance of ceria–zirconia mixed oxides as soot combustion catalysts. Identification of the role of “active oxygen” production

Soot combustion experiments with O 2 and with O 2 + NOx mixtures were performed with model and real soot samples and with a Pt-catalyst and several Ce–Zr catalysts. It was demonstrated that all the Ce–Zr catalysts tested are more effective for soot combustion (due to the important production of active oxygen), than the Pt-catalyst is, even though the noble metal yielded the highest NO 2 production level. A synergetic effect was observed between the NO 2-assisted and active oxygen-assisted soot combustion for the Ce–Zr catalysts studied. The contribution of the active oxygen generated by these mixed oxides to soot combustion, with regard to the NO 2-assisted combustion, becomes more important as soot combustion temperature increases (because of the decrease of soot reactivity). The properties of the Ce–Zr catalysts affect significantly their active oxygen production capacities.

Catalytic Partial Oxidation of Coke Oven Gas to Syngas over Ni/SiO<sub>2</sub> Catalyst Modified by Rare Earth Metal Oxide in a Membrane Reactor

The performance of Ni/SiO2 Catalysts modified by La2O3, ZrO2 and CeO2 were tested in a BaCo0.7Fe0.2Nb0.1O3-δ (BCFNO) membrane reactor by catalytic partial oxidation of coke oven gas (COG) under atmospheric pressure. The results show that the oxygen permeation flux increased dramatically with Ni/RxOy/SiO2 (R = La, Zr or Ce) catalysts by adding the element of rare earth especially the La during the reforming reaction. At optimized reaction conditions, the dense oxygen permeable membrane had an oxygen permeation flux around 16.4 ml/cm2•min and a CH4 conversion of 99.2% have been achieved at 900 oC.

Synthesis and characterization of Pt/Fe–Zr catalysts for the CO selective oxidation

Catalysts of Pt on Fe2O3 and mixed oxides FexZr(1−x)O2 were prepared for the selective CO+H2 oxidation. X-ray diffraction and Mössbauer spectroscopy showed α-Fe2O3 in pure support, a solid solution for x=0.25 and mixed oxides with segregated phases for higher “x” values. Mössbauer results showed also that with increasing the Zr content Zr4+ ions substitute the Fe3+ ions in the α-Fe2O3 lattice, and also Fe3+ ions diffusing into the zirconia lattice. The Pt/Fe0.25Zr0.75O2(p) exhibited only Fe3+ inside the ZrO2 lattice. After reduction, Fe3O4 was found in the catalysts, which decreased with increasing zirconium loading. It is interesting to note that the corresponding precursor presents 83% of Fe3+ located in the ZrO2 lattice and the remaining 17% corresponds to hematite.Catalytic tests for the preferential oxidation of CO containing H2 showed a maximum CO conversion at different temperatures after reaching total oxygen conversion. The CO conversion decreased with increasing iron content in the mixed oxide. The Pt/Fe2O3 catalyst is the most active compared to the other Pt/mixed oxide and Pt/ZrO2. Results showed the following order: Pt/Fe2O3(c)>Pt/Fe0.75Zr0.25O2(c)>Pt/Fe0.25Zr0.75O2(c)>Pt/ZrO2. The Pt/Fe0.25Zr0.75O2(c) presented high selectivity (56%) at 90°C and is 2-fold higher compared to the Pt/Fe2O3 and Pt/ZrO2 catalyst.

Influence of the physico-chemical properties of CeO 2–ZrO 2 mixed oxides on the catalytic oxidation of NO to NO 2

Commercial and home-made Ce–Zr catalysts prepared by co-precipitation were characterised by XRD, Raman spectroscopy, N 2 adsorption at −196 °C and XPS, and were tested for NO oxidation to NO 2. Among the different physico-chemical properties characterised, the surface composition seems to be the most relevant one in order to explain the NO oxidation capacity of these Ce–Zr catalysts. As a general trend, Ce–Zr catalysts with a cerium-rich surface, that is, high XPS-measured Ce/Zr atomic surface ratios, are more active than those with a Zr-enriched surface. The decrease in catalytic activity of the Ce–Zr mixed oxided upon calcinations at 800 °C with regard to 500 °C is mainly attributed to the decrease in Ce/Zr surface ratio, that is, to the surface segregation of Zr. The phase composition (cubic or t′′ for Ce-rich compositions) seems not to be a direct effect on the catalytic activity for NO oxidation in the range of compositions tested. However, the formation of a proper solid solution prevents important surface segregation of Zr upon calcinations at high temperature. The effect of the BET surface area in the catalytic activity for NO oxidation of Ce–Zr mixed oxides is minor in comparison with the effect of the Ce/Zr surface ratio.

ChemInform Abstract: Zr-Catalyzed Kinetic Resolution of Allylic Ethers and Mo-Catalyzed Chromene Formation in Synthesis. Enantioselective Total Synthesis of the Antihypertensive Agent (S,R,R,R)-Nebivolol.

The first enantioselective total synthesis of the antihypertensive agent (S,R,R,R)-nebivolol (3) is described. The synthesis includes the efficient (EBTHI)Zr-catalyzed kinetic resolutions of cycloheptenyl styrenyl ethers 8 and 16, which are subsequently treated with 4 mol % Mo(CHCMe2Ph)(N(2,6-(i-Pr)2C6H3))(OCMe(CF3)2)2 to afford chiral nonracemic 2-substituted chromenes (R,R)-9 and (S,R)-17. Since the present retrosynthetic analysis dissects the molecule into two chromene fragments, both the (R) and (S) antipodes of (EBTHI)Zr catalyst are required. Accordingly, Buchwald's efficient resolution process is used to resolve rac-(EBTHI)ZrCl2 (from catalytic hydrogenation of commercially available rac-(EBI)ZrCl2), such that the two requisite transition metal chiral catalysts are obtained by a single process. Other noteworthy features of the synthesis include a highly efficient, regio- and stereoselective Pd-catalyzed opening of cyclic allylic epoxide 7 with diaryloxystannane 15 and a photochemical modification o...

An intermetallic Fe–Zr catalyst used for growing long carbon nanotube arrays

Metallic nanoparticles containing single and binary components have been known for their catalytic properties to grow carbon nanotube (CNT) arrays. In this paper, an intermetallic catalyst consisting of iron and zirconium was used to grow millimeter long, well aligned arrays. The Fe–Zr catalysts enabled the growth of 1.7 mm-long carbon nanotube arrays in 45 min. A comparison with pure iron catalyst indicated that adding Zr to iron can stabilize the Fe catalyst at the CNT growth temperature and moderate its reactivity. SEM images showed the different growth behaviors for Fe–Zr and Fe catalysts. The long, uniform CNT arrays grown here have potential applications in many advanced composites.

Enantioselectivity of chiral zirconocenes as catalysts in alkene hydro-, carbo- and cycloalumination reactions

Abstract The enantioselectivity of chiral Zr catalysts L1L2ZrCl2 [L1 = L2 = 1-neomenthylindenyl (Ind∗), 1; L1 = Cp, L2 = Ind∗ 2; L1 = Cp, L2 = 1-neomenthylindenyl-4,5,6,7-tetrahydroindenyl (Cp∗) 3] in the hydro-, carbo- and cycloalumination of alkenes by organoaluminium compounds (OAC) (AlMe3, AlEt3, HAlBu 2 i ) has been studied. It was found that OAC exhibit the most effect on the reaction chemo- and enantioselectivity. The reaction chemo- and enantioselectivity depend on the catalyst structure and reaction conditions (solvent type, catalyst concentration, temperature) as well. It is shown that the lack of asymmetric induction in the reaction of α-methylstyrene hydroalumination by HAlBu 2 i , catalyzed with complexes 1 or 3, is the result of the formation of Zr hydride complexes of different structures as reaction intermediates. MTPA was used as a derivatization reagent for the enantiomeric excess estimation and absolute configuration assignment of β-chiral alcohols obtained after the oxidation and hydrolysis of the reaction products. The applicability of MTPA for the assignment of the absolute configuration of the stereogenic centre in β-ethyl substituted primary alcohols and β-alkyl-1,4-butanediols is shown.

Influence of Zr catalyst on reversible hydrogen storage characteristics of NaAlH4 and Na3AlH6

The cell parameters, electron localization function and density of states of pure and Zr-doped NaAlH4 and Na3AlH6 are investigated using plane-wave pseudo-potential method based on density functional theory. The results show that NaAlH4 and Na3AlH6 are insulators characterized by a band gap of 46 and 31 eV, respectively. The Al and H atoms form covalent bonds and the Na and H atoms form ionic bonds in NaAlH4 and Na3AlH6 When Zr replaces Na, the interaction between Zr and H is stronger than the primary Na—H bond, and the interaction between Al and H becomes weaker; when Zr replaces Al, the bond between Zr and H is weaker than the primary Al—H bond. Our calculations indicate that Zr-doped NaAlH4 and Na3AlH6 are more stable than that of the pure alanates, and the energy to remove H atom is significantly decreased.

A performance study of methanol steam reforming microreactor with porous copper fiber sintered felt as catalyst support for fuel cells

A porous copper fiber sintered felt (PCFSF) as catalyst support is used to construct a methanol steam reforming microreactor for hydrogen production. The PCFSF has been produced by solid-state sintering of copper fibers which is fabricated using the cutting method. The impregnation method is employed to coat Cu/Zn/Al/Zr catalyst on the PCFSF. In this study, the effect of the porosity and manufacturing parameters for the PCFSF on the performance of methanol steam reforming microreactor is studied by varying the gas hourly space velocity (GHSV) and reaction temperature. When the 80% porosity PCFSF sintered at 800 °C in the reduction atmosphere is used as catalyst support, it is found that the microreactor shows remarkable superiority in the methanol conversion and H 2 flow rate in comparison to the ones fabricated under other manufacturing parameters. Moreover, the microreactor with this catalyst-coated PCFSF also demonstrates the excellent stability of catalytic reaction in the methanol steam reforming process.

Copolymerization of ethylene and norbornene by zirconium complexes containing symmetrically tuned trianionic ligands

Homo and copolymerization of ethylene and cyclic olefins were carried out using C 3 symmetric N[CH2CH(Ph)O]3ZrCl (1-ZrCl) and also pseudo-C s symmetric N[CH2CH(Ph)O]3ZrCl (2-ZrCl) catalyst systems upon activation with MAO. Incorporation of comonomer into the polyethylene back bone was mainly governed by catalyst symmetry. Norbornene (NB) incorporation was as high as 40% in the ethylene–norbornene copolymer (ENC) using C 3 symmetric 1-ZrCl/MAO catalyst system and 25% in the case of the pseudo-C s symmetric analogue 2-ZrCl. Unlike the more efficient titanium analogues, the copolymerization of ethylene and NB showed a marginal decrease in catalyst activity and NB incorporation on switching over to the Zr analogues. The aluminum to metal ratio required for catalyst activation was higher for the Zr catalysts compared to that of its Ti analogues. 13C NMR spectral studies on the copolymer clearly indicated the incorporation of NB in an alternating manner.

Selective catalytic reduction of NO with CO on Pt/W–Ce–Zr catalysts

Various Pt catalysts (Pt/ZrO2, Pt/CeO2, Pt/CeZrO, Pt/WO3/ZrO2 and Pt/WO3/CeZrO) were prepared and characterized, and their catalytic reduction reactions of NO by CO, with or without the presence of excess oxygen, were investigated. The results of temperature-programmed experiments showed that CO could be easily oxidized over Pt/CeO2 and Pt/CeZrO while the introduction of WO3 into the catalyst (Pt/WO3/CeZrO) inhibited the reduction of catalyst surface; NO could not dissociate over those catalysts in oxidized state but after CO reduction at a low temperature, NO dissociation took place only over Pt/CeO2 and Pt/CeZrO catalysts. For NO + CO reaction, those easily reduced catalysts Pt/CeO2 and Pt/CeZrO exhibited better catalytic performances, and NO could be rapidly converted below 350 °C. For the reaction with the presence of excess O2, the NO conversions were significantly inhibited, but better NO conversions were obtained over the tungstate-contained catalysts when compared with Pt/CeO2 and Pt/CeZrO. The higher activities of Pt/W–Ce–Zr catalysts were attributed to their high acidities.

Selective hydrogenation of maleic anhydride to γ-butyrolactone and tetrahydrofuran by Cu–Zn–Zr catalyst in the presence of ethanol

A series of Cu–Zn–Zr catalysts were prepared by a coprecipitation method and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, temperature programmed reduction, and N 2 adsorption. The catalytic activity of the Cu–Zn–Zr catalyst in the hydrogenation of maleic anhydride using ethanol as a solvent was studied at 220–280 °C and 1 MPa. Maleic anhydride was mainly hydrogenated to γ-butyrolactone and tetrahydrofuran while ethanol dehydrogenated to ethyl acetate. After reduction, CuO species present in the calcined Cu–Zn–Zr catalysts were converted to metallic copper (Cu 0). The presence of ZrO 2 favored the deep hydrogenation of γ-butyrolactone to tetrahydrofuran while the presence of ZnO was beneficial to the formation of the intermediate product γ-butyrolactone. The molar ratios of the hydrogen produced in ethanol dehydrogenation to the hydrogen consumed in maleic anhydride hydrogenation increased with the increase of the reaction temperature.