Structure of MnZr mixed oxide catalysts and their catalytic properties in the CO hydrogenation reaction

doi:10.1016/0021-9517(92)90312-6

Journal of Catalysis

Volume 138, Issue 2, December 1992, Pages 630-639

https://doi.org/10.1016/0021-9517(92)90312-6 Get rights and content

Abstract

MnZr oxide catalysts with varying MnZr ratio were prepared by a coprecipitation method. Their structure and catalytic properties were studied by means of N₂ adsorption, XRD, TPR, and CO hydrogenation as a probe reaction. The precipitated MnZr mixed oxide was composed of a mixture of large particles of manganese oxide and small particles of zirconium oxide. Addition of Mn retarded the growth of fine particles of zirconium oxide. By calcination at high temperature, part of the manganese oxide forms a solid solution with zirconium oxide and deposits on the surface of zirconium oxide as a thin layer. The type of Mn present in the mixed oxide affected the selectivity pattern in the CO hydrogenation. The bulk Mn exhibited a high selectivity to isobutene, but products contained hydrocarbons higher than C₅. Mn dispersed on the surface of zirconium oxide showed a similar selectivity pattern to bulk Mn, but hydrocarbon chain growth was limited to C₄ or lower. The formation of a solid solution enhanced production of lower hydrocarbons, especially methane.

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2020, Materials Letters
Citation Excerpt :
Manganese based oxides are active catalysts in several oxidation and reduction reactions, such as oxidation of CO, volatile organic compounds [1], selective reduction of nitrobenzene to nitrobenzene to nitrosobenzene and NOx with NH3 [1,2–4], CO hydrogenation [5].
Mn-Zr oxide catalyst was studied by X-ray powder diffraction and mass-spectrometry under CO oxidation reaction conditions with different CO/O₂ ratio. Mn-Zr catalyst consists of manganese oxides and Mn_yZr_1–yO_2–x solid solution and was found to be stable in the environment with stoichiometric ratio of CO/O₂ = 2:1 and with excess of oxygen. When the catalyst is treated in the reducing environment (pure CO and CO/O₂ = 4:1) the transformation of manganese oxides to MnO and reduction of manganese cations in the structure of Mn_yZr_1–yO_2–x are observed. This process is reversible and reoxidation leads to the formation of the catalyst similar to the initial.
Local structure and short-range ordering of MnO<inf>2</inf>-Ce<inf>(1 - X)</inf>Zr<inf>x</inf>O<inf>2</inf>/TiO<inf>2</inf>
2015, Materials Characterization
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Although the amplitude of the peak that was observed at ~ 5.15 Å was low (due to the irregular order in the amorphous phase), this peak was considered to show the Ce–Mn bond. There is high degree of chemical interaction and affinity between Mn and Zr, thereby an Mn–Zr mixed oxide has been used for various applications, such as Mn-stabilized zirconia, volatile organic compounds (VOC) removal catalysts and CO hydrogenation catalysts [45–49]. Mn has various valence states, but Mn2O3 (Mn3 +) and MnO2 (Mn4 +) are common phases after calcination in the temperatures of about 550 °C.
The mechanism of the dispersion improvement in Zr-added MnO_x–CeO₂/TiO₂ is investigated. Through crystallographic analyses of the catalyst powder synthesized by the sol–gel method, it was observed that the MnO_x–CeZrO₂ (catalytic materials) formed on TiO₂ was in amorphous phase. The aggregation of Ce occurs in MnO_x–CeO₂/TiO₂, while all catalytic materials are well-dispersed with the Zr addition, which is attributed to the formation of Zr–Mn bonding. The result from X-ray absorption fine structure (EXAFS) analysis at Ce L₃-edge revealed that the amorphous phase formed on a TiO₂ particle was arranged in order of Ce, Zr and Mn. The Mn^4 +/Mn^3 + ratio increased from 0.84 to 2.36 with increasing addition of Zr, supporting the result obtained from Differential Scanning Calorimetry (DSC) analysis. Catalytic activity was evaluated to identify the effect of dispersion and the improvement of the de-NO_x efficiency was approximately 50% at 150 °C, which can be explained by large contact area between Mn and Ce.
Supported manganese oxide on TiO<inf>2</inf> for total oxidation of toluene and polycyclic aromatic hydrocarbons (PAHs): Characterization and catalytic activity
2013, Materials Chemistry and Physics
Citation Excerpt :
Two reduction peaks centred at 410 and 524 °C were obtained. According to literature [33], these peaks have been attributed to MnO2 and Mn2O3 reductions respectively. The coexistence of these two oxide phases, before reduction, was confirmed by XRD measurements.
Manganese oxide catalysts supported on titania (TiO₂) were prepared by incipient wetness impregnation method in order to elaborate catalysts for total oxidation of toluene and PAHs. These catalysts have been characterized by means of X-ray diffraction (XRD), electron paramagnetic resonance (EPR), temperature programmed reduction (TPR) and temperature programmed desorption (TPD). It has been shown that for the 5%Mn/TiO₂ catalyst the reducibility and the mobility of oxygen are higher compared, in one side, to other x%Mn/TiO₂ samples and, in another side, to catalysts where TiO₂ support was replaced by γ-Al₂O₃ or SiO₂. It has been shown that the content of manganese loading on TiO₂ has an effect on the catalytic activity in the toluene oxidation. A maximum of activity was obtained for the 5%Mn/TiO₂ catalyst where the total conversion of toluene was reached at 340 °C. This activity seems to be correlated to the presence of the Mn³⁺/Mn⁴⁺ redox couple in the catalyst. When the Mn content increases, large particles of Mn₂O₃ appear leading then to the decrease in the corresponding activity. In addition, compared to both other supports, TiO₂ seems to be the best to give the best catalytic activity for the oxidation of toluene when it is loaded with 5% of manganese. For this reason, the latter catalyst was tested for the abatement of some PAHs. The light off temperature of PAHs compounds increases with increasing of benzene rings number and with decreasing of H/C ratio. All of PAHs are almost completely oxidized and converted at temperatures lower than 500 °C.
Co-doping a metal (Cr, Fe, Co, Ni, Cu, Zn, Ce, and Zr) on Mn/TiO<inf>2</inf> catalyst and its effect on the selective reduction of NO with NH<inf>3</inf> at low-temperatures
2011, Applied Catalysis B: Environmental
Citation Excerpt :
It is known that zirconium oxide has two different surface hydroxyl groups (bridged and terminal). We ascribe the characteristic broad TPR peak at 894 K to the reductions of these two hydroxyl groups [26]. Addition of zirconia does not create any variation in the reduction pattern of Mn/TiO2 catalyst.
A series of Mn–M′/TiO₂ (M′ = Cr, Fe, Co, Ni, Cu, Zn, Ce, and Zr) catalysts were prepared using incipient wetness technique and investigated for the low-temperature selective catalytic reduction (SCR) of NO with ammonia in the presence of excess oxygen. A combination of various physico-chemical techniques was used to investigate the influence of co-doped metals on the characteristics of Mn/TiO₂ catalyst. The catalytic performance of these materials was compared with respect to the M′/Mn atomic ratio in order to examine the correlation between physicochemical characteristics and reactivity of optimized materials. XRD results suggest that metal oxide species exist in a highly dispersed state at a certain level called two-dimensional monolayer coverage. Our XPS results illustrated that the MnO₂ phase is extremely dominant over the Mn₂O₃ phase (Mn⁴⁺/Mn³⁺ = 22.31, 96%) in the Mn–Ni(0.4)/TiO₂ anatase catalyst, whereas Mn₂O₃ phase is in competition with MnO₂ in other catalysts (Mn⁴⁺/Mn³⁺ = 1.34–12.67). H₂-TPR data results are in good accordance with XPS results that the absence of the high-temperature (736 K) peak indicates that the dominant phase is MnO₂ in Mn–Ni(0.4)/TiO₂ catalyst. This increase in reducibility of manganese and dominant MnO₂ phase seems to be the reason for the superior activity and time on stream patterns of our best catalyst. BET and pore volume measurements revealed high surface area and pore volume of the Mn–Ni/TiO₂ catalyst. The in situ NH₃-FTIR results suggest that the manganese (Mn/TiO₂) and manganese–nickel (Mn–Ni/TiO₂) surface sites have only Lewis acidity, with no apparent Brönsted acidity. The catalytic performance of various Mn–M′/TiO₂ (M′/Mn = 0, 0.2, 0.4, 0.6, 0.8) catalysts was studied for the low-temperature SCR reaction at a range of temperatures (160–240 °C) under industrial conditions using GHSV = 50,000 h⁻¹. The intrinsic activity of Mn–Ni/TiO₂ catalyst with M′/Mn = 0.4 atomic ratio measured under differential reaction conditions, was found to be highly active, selective and broadening the temperature window for this reaction.
Hydrothermal preparation of nanostructured manganese oxides (MnO<inf>x</inf>) and their electrochemical and photocatalytic properties
2011, Chemical Engineering Journal
Citation Excerpt :
Manganese oxides nanomaterials with notably increased surface area and greatly reduced size have been widely used in many applications [15,16]. In particular, due to their ion-changing, molecular adsorption, electrochemical and magnetic properties [17], Manganese oxides catalysts exhibit considerable activity in oxidation–reduction reactions; they are among the most efficient transition-metal oxides catalysts for gas-phase reactions, such as carbon monoxide hydrogenations [18], high-temperature methane combustion [19,20] and the selective catalytic reduction of nitric oxide by hydrocarbons [21,22] and by ammonia [23–25], as well as for epoxidation reactions. Recently, manganese dioxide nanocrystals have been used for the degradation of methylene blue, [26–29] rhodamine B, [29,30] Congo red and ethylene blue. [30].
Manganese oxides nanomaterial (MnO_x) with crystalline phases of MnOOH nanorod and Mn₃O₄ octahedron-like were synthesized by hydrothermal method based on the redox reaction between MnO₄⁻ and CH₂O at 120 °C and 200 °C for 10 h, respectively. The β-MnO₂ nanowires were prepared by calcining MnOOH nanorods at 300 °C for 3 h in air. Particles were characterized by XRD, FE-SEM, TEM, SA-ED, HR-TEM, Brunauer–Emmett–Teller (BET) and UV–vis diffuse reflectance spectroscopy. Their capability of catalytic degradation of alizarin yellow R with air oxygen in aqueous under visible light irradiation and electrochemical properties of as-prepared nanocrystal modified with carbon paste electrode were comparatively studied. The degradation products were determined by GC–MS. In addition, some influences factors, such as pH and temperature on the photocatalytic degradation were also investigated. Among the as-prepared MnO_x nanostructures, β-MnO₂ nanowire exhibit higher specific capacitance and better catalytic activity than Mn₃O₄ octahedron-like and MnO(OH) nanorod. The hydroxyl radical mechanism of the photocatalytic degradation of alizarin yellow R was detected and discussed.
Preparation of Cu<sup>+</sup>/SiO<inf>2</inf>-ZrO<inf>2</inf> catalysts for oxidative carbonylation of methanol to dimethyl carbonate
2011, Ranliao Huaxue Xuebao/Journal of Fuel Chemistry and Technology
Silica-zirconia mixed oxide (SiO₂-ZrO₂) was synthesized by sol-gel method; with SiO₂-ZrO₂ as the support, CuCl₂/SiO₂-ZrO₂ catalyst was then prepared by ion-exchange and used in the liquid oxidative carbonylation of methanol to dimethyl carbonate (DMC). The results showed that the introduction of zirconium species into the amorphous silica leads to the formation of Si-O-Zr bonds and Brønsted acid sites. When the CuCl₂/SiO₂-ZrO₂ catalyst is calcined at 300–550°C in an inert atmosphere, CuCl₂ is dispersed and bounded on the surface of SiO₂-ZrO₂ support; CuCl₂ can be auto-reduced to CuCl, which is then ion-exchanged with the surface Brönsted acid sites of the SiO₂-ZrO₂ support to form Cu⁺ species. As a result, most of copper remains to be highly dispersed on the surface of SiO₂-ZrO₂ and only a small amount of chlorine is left over. The CuCl₂/SiO₂-ZrO₂ catalyst calcined at 450°C exhibits excellent activity in the oxidative carbonylation of methanol; under the conditions of 140°C, 2.4 MPa and a CO/O₂ ratio of 2, the conversion of methanol and the selectivity to DMC reach 10.0% and 79.4%, respectively.

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Structure of MnZr mixed oxide catalysts and their catalytic properties in the CO hydrogenation reaction

Abstract

Appl. Catal.

Appl. Catal.

J. Mol. Catal.

J. Catal.

J. Catal.

J. Catal.

J. Catal.

J. Catal.

Appl. Catal.

J. Catal.

J. Catal.