BiMo Catalysts Research Articles

Bi3.64Mo0.36O6.55 nanoparticles anchored in BiOI: A p-n heterojunction photocatalyst to enhance water purification

Selective constructing of heterojunctions enables directional electron-hole migration and favorable charge separation. In this study, a novel p-n junction Bi3.64Mo0.36O6.55 (BMO) nanoparticles anchored in BiOI construct by hydrothermal and subsequent in-situ synthesis. The construction of tight heterojunctions that enhance the characteristic absorption of visible light by Bi3.64Mo0.36O6.55/BiOI (BIMO) and expose more reactive sites can be used to facilitate the rapid degradation of antibiotics (Tetracycline, TC), endocrine disruptors (Bisphenol A, BPA) and dyes in water. In addition, the BIMO catalyst maintained the rapid degradation rate of TC despite the interference of inorganic anions and aqueous substrates. The charge transfer pathways and radical species between the heterojunction components were investigated. In addition, the intermediates and toxicological analysis showed that TC was further mineralized and the small molecule products were generated significantly less toxic and less contaminated. In conclusion, this study synthesized photocatalysts based on p-n heterojunctions, which have potential applications for the degradation of TC.

The Synergy Effect in Tio2 Supported Bi-Mo Catalysts for Facile and Environmentally-Friendly Synthesis of Pyridylaldehydes from Oxidation of Picolines

The oxidation of picolines to pyridlaldehydes was studied over bismuth molybdate catalysts supported on TiO2. The research results showed that α-Bi2Mo3O12 was superior to β-Bi2Mo2O9 and γ-Bi2MoO6 in terms of reactivity. Further doping MoO3 to α-Bi2Mo3O12/TiO2 gave rise to increased catalytic performance, which was due to the synergy effect of α-Bi2Mo3O12 and MoO3. The effect was on one hand manifested in the intimate relationship between α-Bi2Mo3O12 and MoO3 in stabilizing the crystallographic structure of catalysts and thereafter maintaining the surface area of the catalyst, as indicated by the BET surface area and XRD analysis. Moreover, NH3-TPD analysis demonstrated the effect in modifying the surface acidity of the catalysts, and thus facilitating the substrate adsorption as the picolines are alkaline substances. Additionally, the effect between α-Bi2Mo3O12 and MoO3 rendered the modification of the electronic properties and thereafter the oxygen desorption properties and reducible properties of the catalysts, as evidenced in the H2-TPR and O2-TPD analysis.

Investigation of propene oxidation to acrolein by the method of ultralow conversion: A new mechanism of the reaction

Investigation of reaction mechanisms by identifying the intermediates released into the gas phase is most effective at low conversion of reactants, ideally approaching zero. However, conversions below 0.5–1% are rarely used, due to the difficulty of analysis of low-concentration products. The mechanism of the title reaction is a subject of long-term discussion. We studied the mechanism using an original ultralow conversion (ULC) method. The idea is to perform the analysis of products after their preliminary accumulation in a suitable absorbent at the reactor outlet. This allows decreasing conversion by 2–3 orders of magnitude. The ULC experiments were conducted with a Bi–Mo catalyst at 100–250 °C and with propene conversion down to 0.001%. A new so-called allyl hydroxylation mechanism was revealed. A key step is the hydroxylation of the CH3 group to form an allyl alcohol intermediate, which is further oxidized to acrolein. The mechanism explains all reaction features and was confirmed by experiments at 350 °C.

Quasi-Catalytic Identification of Intermediates in the Oxidation of Propene to Acrolein over a Multicomponent Bi–Mo Catalyst

The generally accepted three-step mechanism of propene oxidation to acrolein includes abstraction of two hydrogen atoms and addition of one oxygen atom. The first step is a well-known H-abstraction from the methyl group. The sequence of two other steps is unclear. We investigated the reaction in quasi-catalytic mode at 100–200 °C with extraction and analysis of accumulated surface products. The reaction intermediate, surface ether of allyl alcohol, was identified. This strongly proves that O-addition precedes the second H-abstraction. Activation energy and kinetic isotope effect of the quasi-catalytic reaction correlate with appropriate parameters of the conventional catalytic process.

The role of active phase in Ce modified BiMo catalysts for oxidative dehydrogenation of 1-butene

BiMoCex catalysts (x=0–0.4) were prepared by co-precipitation method and tested in the oxidative dehydrogenation (ODH) of 1-butenes to 1,3-butadiene. The results indicate that the cerium content has significant effects on the performance of catalyst. BiMoCe0.2 exhibits the superior activity and stability during the 100h test. X-ray photoelectron spectroscopy (XPS), temperature-programmed re-oxidation (TPRO), 1-Butene temperature-programmed desorption (TPD) and pulse O2 adsorption characterization reveal that the oxygen mobility and the adsorption ability of 1-butene of catalysts are two crucial factors determining catalytic performance in ODH reaction. The active phases on BiMoCex play different roles in the reaction.

Role of shaping in the preparation of heterogeneous catalysts: Tableting and slip-casting of oxidation catalysts

The process and impact of shaping mixed vanadium aluminum (hydr)oxides, VAlOH and VAlO, respectively, and BiMo catalysts by tableting and slip-casting were examined. Graphite (G) was employed as a shaping agent for tableting. Without it tableting was impracticable. Graphite was found to enhance the mechanical resistance of VAlOH-xG and BiMo-xG and changed the surface area by increasing it for the non-porous BiMo and by decreasing it for the mesoporous VAlOH. In addition, graphite modified the catalytic performance despite changing neither the chemical nor the structural state of the base VAlO(H) and BiMo catalysts. A positive effect on the performance of VAlO-xG in propane oxidative dehydrogenation was found. It was proposed that catalytic active sites are formed on graphite during calcination. Conversely, graphite was harmful for non-calcined VAlOH-xG and BiMo-xG. On the other hand, the preparation of chemically and physically stable VAlO(H) suspensions for slip-casting was accomplished. Chemical stability was achieved at pHs near the isoelectric point of these catalysts. For physical stability, the use of a dispersing agent, poly(acrylic acid), combined with a control of the solids concentration was necessary. A simple and reliable method for preparing VAlOH and BiMo pellets by slip-casting was thus developed with the use of colloidal silica as binding agent. The so prepared pellets were mechanically resistant and kept the surface area of the base materials. A decrease in the surface concentration of the active metals due to surface active site masking by silicon for VAlOH-xSi and BiMo-xSi led to an inferior catalytic performance.

Partial oxidation of propane to acrolein in a dual bed inert membrane reactor

The partial oxidation of propane to acrolein is studied in a dual bed membrane reactor. A porous membrane tube is used to feed oxygen to the annular catalyst beds surrounding the porous section of the membrane tube. The distributed oxygen feed in the membrane tube lowers the partial pressure of oxygen in each bed increasing selectivity to the partially oxidized product over total oxidation. The first bed contained a V/MgO catalyst for the partial oxidation of propane to propene. The second bed consisted of a BiMo catalyst to convert propene to acrolein. Studied were conducted first in each bed separately to determine operating conditions in each bed and then in a dual bed configuration. The separate inert membrane reactors show improvement in selectivity of few % in comparison to fixed bed reactors. On the other hand when using both membrane reactors combined in a dual bed configuration a major improvement in acrolein selectivity of up to 21% was obtained. Catalysts characterization by surface area, X-ray diffraction, and X-ray photoelectron spectroscopy showed that the improvement was due to the distribution of the oxygen flow rate through the membrane in the second membrane reactor which prevented the deactivation of the BiMo catalyst.

Selective oxidation of isobutene to methacrolein on multiphasic molybdate-based catalysts

Synergetic effects in the selective oxidation of isobutene to methacrolein have been studied over catalysts containing several molybdate phases. Two types of catalysts have been analysed: (1) pure bismuth molybdates with Bi/Mo ratios of 2/2 and 2/3[BiMo(2/2)and BiMo(2/3)] and cobalt molybdate [Co/Mo(1/1)]; and (2) multiphasic molybdates consisting of three or four molybdates prepared by: (a) coprecipitation of cobalt and bismuth salts and calcination at high temperatures, (b) mechanically mixing in dry conditions the separate molybdates and calcining at high temperatures and (c) dispersing the separate molybdates in n-pentane and calcining at high temperatures. Synergetic effects are observed in multiphasic Bi/Mo(2/2)CoMo and BiMo(2/3) catalysts. For BiMo (2/2)CoMO catalysts the highest synergetic effects in the conversion, yield and selectivity are observed. For the catalysts before test no new phase is formed after calcination while after test X-ray measurements indicate a practically complete transformation of α-Bi 2Mo 3O 12 into γ-Bi 2MoO 6 and MoO 2 and traces of MoO 3 and Bi 2x Mo 1−xO 3. Neither contamination between phases is observed. The synergetic effects are explained by the cooperation between separate γ-Bi 2MoO 6, MoO 3 and (α+β)-CoMoO 4 phases in contact. The cooperation between phases is more effective when MoO 3 is present in a large proportion.

Co Oxidation by Bi2MoO6-γ(H) Catalyst

ABSTRACTWe present a study of a Bi-Mo catalyst, obtained by solid state reaction, for the oxidation of CO. Bismuth-molybdate catalysts form several phases (β3-Bi2Mo2O9, α-Bi2Mo3O12 and γ-Bi2MoO6, among others), depending upon the Bi/Mo ratio and the preparation method [1]. The γ-Bi2MoO6 phase is the one that is stable at high temperatures, according to the phase diagram, and is the one we used as catalyst for the conversion of CO [2].

Structure and catalytic activity characterization of bismuth molybdate catalysts

We present a study of Bi-Mo catalysts prepared from pure oxides (MoO3 and Bi2O3) by solid state reaction methods. The structure characterization by X-ray diffraction shows only the low temperature (koechlinite) and high temperature (γ(H)) phases in varying proportions depending on the calcination temperature. The carbon monoxide oxidation shows a synergetic effect for mixed oxides as compared to pure oxides. Significant differences in catalytic activity, surface morphology and surface concentration were observed when the molybdenum precursor was changed from molybdenum trioxide to ammonium heptamolybdate in the catalyst preparation.

Stability aspects and olefine adsorption properties of Bi 2Mo 2O 9 and of the silica-supported Bi 9PMo 12O 52 catalyst

The adsorption of 1-butene and butadiene on Bi 2Mo 2O 9 and on silica-supported Bi 9PMo 12O 52 catalyst was measured. Both catalysts (in which the Erman phase is the major component) show weak single-site adsorptions of 1-butene and butadiene and a slow but strong adsorption of butadiene. Thermal decomposition of the Erman phase into Bi 2O 3 · 3MoO 3 and Bi 2O 3 · MoO 3 runs parallel with a change of the weak single-site type of adsorption into a dual-site type of adsorption, well known as belonging to the koechlinite phase. The silica-supported catalyst is thermally more stable than the Bi 2Mo 2O 9 compound. The supported catalyst is found to be partially unstable if exposed to reduction-reoxidation conditions at 470 °C. Suggestions are given as to the role of P in silica-supported Bi-Mo catalyst.

Bismuth molybdate catalysts. Preparation, characterization and activity of different compounds in the BiMoO system

The influence on oxidation activity of the method of preparation of BiMo catalysts and in particular the circumstances during the wet stage (precipitation, slurry reactions between preprecipitated oxyhydrates) have been investigated. It was found that active Bi Mo = 2 1 catalysts have to be prepared by a slurry reaction starting from what is essentially (BiO) (NO 3). Even the application of powdered crystals of compounds with this composition leads to active catalysts. Contrary to previous work, active 1 1 catalysts can only be prepared by precipitation but the phase formed is not stable against prolonged heating at temperatures around 500 °C.

Adsorption and heat of adsorption of propylene on a BiMo oxide catalyst

The adsorption isotherms of propylene were determined on a BiMo SiO 2 oxide catalyst in the range of 37–150 °C and on a BiMo oxide catalyst without carrier at 35 °C. For the individual propylene doses, the adsorption heats were also determined calorimetrically. The adsorption heat of propylene on the BiMo SiO 2 catalyst is equal to 8 kcal/ mole, independently of the surface coverage, whereas the adsorption heat on the BiMo catalyst decreases with the coverage of the surface from 12 to 2 kcal/mole. In measurements carried out at 170 °C, the adsorption of propylene is followed by a consecutive process i.e., the oxidation of propylene to acrolein, which is accompanied by reduction of the catalyst. Oxygen is adsorbed from this catalyst at the same temperature with a high heat of adsorption, 75 kcal/mole, in an amount exceeding the preceding amount of adsorbed propylene by about 13%. Moreover, the adsorption of propylene from a propylene-oxygen mixture was also investigated. The results obtained are discussed with regard to the interaction between propylene and the surface of the BiMo SiO 2 oxide catalyst, and an attempt has been made to evaluate the reaction mechanism of the oxidation of propylene to acrolein from the viewpoint of thermochemical data.

Oxidation of 1-butene over UO 3Sb 2O 3 catalysts

The oxidative dehydrogenation of butene to butadiene over USb catalysts was investigated. The presence of two compounds, reported by Grasselli and Callahan, was confirmed with one being the actual catalyst. The reaction is first order in butene and zero order in oxygen. In the absence of oxygen, interaction of butene with the catalyst oxygen occurred but only to a minor degree, the interaction being confined to the surface. Partial reactivation by heating of a catalyst inactivated by the interaction with butene in the absence of O 2 could be effected, but there exists a tendency for the catalyst to decompose. A remarkable detail in the kinetics is that, contrary to the reaction over BiMo catalyst, double-bond isomerization is absent.

Adsorption equilibria and rates of reactions of adsorbed compounds on reduced and oxidized BiMo catalysts

The adsorption equilibria of the butenes, butadiene and H 2O were determined on fully oxidized or partially reduced BiMo catalysts as a function of the degree of reduction. The rate of reduction of the catalysts by butene and by butadiene and the rate of oxidation of reduced catalysts by O 2 were also studied in their dependence on the degree of reduction. The adsorption isotherms were found to follow simple Langmuir laws, either of the single or of the dual site type. This behavior was reflected in a linear or quadratic decrease or increase of the maximal volume adsorbable as a function of the degree of reduction. The adsorption of the hydrocarbons decreased with increasing reduction; that of water and oxygen proved to be zero on oxidized catalysts but to increase with increasing reduction. Two types of adsorptive centers could be distinguished in this way, viz., 1. (1) a single site that adsorbs butadiene in a slow but strong adsorption and that also acts as the adsorption site for H 2O and 1 2 O 2 in the reduced state (A center). 2. (2) a combination of three sites, two of which adsorb 1-butene, cis-2-butene but also butadiene in a fast but weak adsorption, the third one adsorbing trans-2 in a single site adsorption (B center). The conversion of butene to butadiene was found to be a bifunctional process that involves the simultaneous cooperation of A and B centers. Combustion on the other hand starts from single A centers. Reoxidation also proceeds from the vacant A centers provided the temperature does not exceed 400 °C. Above this limit a new process sets in, the rate of which is not determined by a diffusional process but instead by a surface reaction. The nature of the latter process is still obscure. The heat of adsorption of H 2O on the reduced A centers was found to be so low as to provide an explanation for the absence of an inhibition by water in the conversion to butadiene.

The catalytic oxidation of 1-butene over bismuth molybdates: Promoters for the Bi 2O 3·3MoO 3 catalyst

The effect of the promoters BiPO 4, Fe 2O 3, and Cr 2O 3 on the catalytic activity of the moderately active Bi 2O 3·3MoO 3 catalyst ( 2 3 ) were investigated for the oxidation of butene to butadiene. All compounds if present in quantities equivalent to 10% (mole ratio's) show a pronounced promoting effect. For two of the three promoters, BiPO 4 and Fe 2O 3, it could be shown that for these concentrations the promoter action is caused by the formation of the far more active Bi 2O 3·MoO 3 (Koechlinite) phase ( 2 1 ). This conclusion is consistent with the observations that the 2 1 lines appear in the X-ray diagrams. The kinetics of the reaction shift to those earlier observed for the 2 1 phase and finally that the adsorptive properties for butene and butadiene become more similar to those earlier reported for 2 1 than for 2 3 . The catalytic properties of the system Bi 2O 3·3MoO 3 + Fe 2O 3·3MoO 3 were studied in the entire range from Bi to Fe. It was found that a new compound (X) is formed possessing an X-ray diagram not earlier found by us but occasionally reported on technical BiMo catalysts by other authors. The compound X exists along the entire range from Bi to Fe = 8 2 to 1 9 . It possesses a fairly strong activity for the butene-butadiene conversion and is also a selective catalyst.

Pulsed chromatographic study of the poisoning of a bismuth-molybdenum catalyst of the oxidative dehydrogenation of isoamylenes

1. The influence of treatment of a Bi-Mo catalyst with quinoline on the oxidative dehydrogenation and isomerization of isoamylenes was studied by a pulsed chromatographic method. 2. The measured activation energies on poisoned and unpoisoned catalysts indicate an inhomogeneity of the catalytic surface. The logarithm of the relative rate constant of oxidative dehydrogenation drops as a linear function of the amount of poison introduced. 3. Quinoline most strongly suppresses profound oxidation, then oxidative dehydrogenation, and has the least effect on isomerization.

Catalytic Oxidative Dehydrogenation of Hydrocarbons (Part 1)

The oxidative dehydrogenation reaction of n-butene to butadiene over Bi-Mo, Bi oxide and Mo oxide catalysts in a flow system at atmospheric pressure has been investigated.High butadiene yield were obtained over Bi-Mo coprecipitation catalyst at 400∼500°C in excess of oxygen, but higher oxygen content lowered the butadiene selectivity with increase in CO and CO2 formation.The order of oxidative dehydrogenation over the investigated catalysts can be shown as follows, Bi-Mo(coprecipitation)>Bi2O3+MoO3(dry mixing)>MoO2.76>MoO3>Bi2O3_??_Silica chip.When oxidation reaction of hydrogen compared with oxidative dehydrogenation of n-butene at the same conditions, it was assumed that oxidative dehydrogenation over Bi-Mo and MoO3 catalysts was not dehydrogenation followed by oxidation of hydrogen.Oxidation reaction of n-butene over Bi2O3 catalyst may undergo in different mechanism from oxidative dehydrogenation over Bi-Mo catalyst.

Oxidative dehydrogenation study of isoamylenes over a Bi-Mo catalyst

Oxidative dehydrogenation study of isoamylenes over a Bi-Mo catalyst