Ind. Eng. Chem. Res. 2008, 47, 1011-1016
1011
Phase Composition and Catalytic Activity of r-NiMoO4 Reduced with Hydride Anion Hany M. AbdelDayem* Chemistry Department, Faculty of Science, Ain Shams UniVersity, 11566-Abassia, Cairo, Egypt
Mohamed A. Al-Omair Chemistry Department, Faculty of Science, King Faisal UniVersity, P.O. Box 1759, 31982 Al-Hasa, Al-Hofof, Kingdom of Saudi Arabia
An attempt was carried out to improve the catalytic performance of R-NiMoO4 in partial oxidative dehydrogenation of alkanes. Different catalyst samples were reduced by hydride anion, H-, using CaH2 in the temperature range 100-450 °C. The catalytic performance of the resulting catalyst samples in the oxidative dehydrogenation of cyclohexane at different temperatures and at atmospheric pressure was investigated. The phase composition of molybdate and reduction products was analyzed by XRD. Reduction of R-NiMoO4 with CaH2 at temperatures above 200 °C yielded reduction products consisting of crystalline Ni and MoO2, intermetallic compounds between Ni and Mo, and incompletely reduced R-NiMoO4, whereas reduction of R-NiMoO4 with H2 is not possible under the same conditions applied. Nickel molybdate catalyst, reduced with CaH2 at 450 °C, showed a high selectivity toward cyclohexene at isoconversion (5%), in comparison with that of parent R-NiMoO4 and that of catalyst reduced with hydrogen. In view of the XRD results, the significant high selectivity of this catalyst toward cyclohexene was attributed to the fact that reduction by CaH2 modified the crystal structure “cell dimensions” of the incompletely reduced R-NiMoO4. On the other hand, a synergetic effect between the new phases founded in this catalyst sample after reduction and the incompletely reduced R-NiMoO4 was proposed. 1. Introduction The discovery of new ways to master metal oxide selectivity in catalytic oxidation of alkanes is still a great challenge.1 Different groups of investigators have done several trials in this field by adding gaseous promoters (viz., CO, CO2, NH3, N2O, and H2) to reaction feed.2-4 The presence of hydrogen brought about conspicuous changes in the selectivity of catalytic oxidation reactions, permitting the production of unexpected molecules.5,6 The role of hydrogen in selective oxidation is attracting much attention. Recent investigations suggested that hydrogen modifies the chemical state of the active sites of the catalysts.6 Indeed, controlled reduction of metal oxides using hydrogen could offer a new promising approach for modulating the nature of catalytic oxidation sites. Nickel molybdate catalyst was widely investigated in connection with its industrial application in oxidative dehydrogenation (ODH) of alkanes (C2-C4).7-9 It is well-known that nickel molybdate formed principally in two phases, R- and β-phases, where Mo is in octahedral coordination in the R-phase and tetrahedral in the β-phase. NiMoO4 adopts the R-phase configuration at room temperature, with the β-phase being stable at elevated temperatures, ca. 700 °C.9 Previous investigations have shown that the catalytic performance of this catalyst is closely related to molybdenum coordination, where the β-phase of NiMoO4 is more selective for ODH of alkanes to alkenes than the R-phase.10,11 An effective controlled reduction of R-NiMoO4 using hydrogen gas can open a new gate to modulate Mo coordination and subsequently master catalytic performance. However, the mechanism of reduction of R-NiMoO4 with H2 is still debated, especially at temperatures below 500 °C.7,12,13 * To whom correspondence should be addressed. Tel./Fax: +2024831836. E-mail:
[email protected].
Therefore, there is clearly a need to use reducing agents that are effective at lower temperatures to avoid complete reduction of R-NiMoO4 to their metals. The hydride anion is one of the most powerful reducing agents known; the reduction potential of the H-/H2 couple has been estimated at -2.25 V.14 A variety of highly metastable oxides of specific electronic and magnetic properties were prepared by reduction of complex oxides by the hydride anion using different metal hydrides (viz., LiH, NaH).15-18 Recently, CaH2 has been used as a powerful reducing agent in solid-state topotactic reduction, at lower temperatures than would be required for H2 gas process.19 In addition, CaH2 has a higher decomposition temperature (∼880 °C) than the other solid hydrides, which could be used to carry out solid-state reduction over a wide temperature range. The development of a new synthetic route based on reduction of the metal oxide catalysts using CaH2 can probably provide the possibility of modifying selectivity and/or activity of these catalysts in oxidative dehydrogenation (ODH) of alkanes. In the present work an attempt has been made to produce a change in the molecular structure “coordination” of R-NiMoO4 by controlled reduction using CaH2 at different temperatures.19 The reactivity of all catalysts was tested for the oxidative dehydrogenation of cyclohexane as a model reaction, looking for a significant modification in catalytic performances. H2 was also used to prepare a reference sample. The phase composition of the studied catalysts was investigated by X-ray diffraction (XRD), and the change in the structure “cell dimensions” of R-NiMoO4 was also analyzed. 2. Experimental Section Pure stoichiometric NiMoO4 was prepared by coprecipitation from aqueous solutions of 750 mL of 0.057 M ammonium
10.1021/ie070793z CCC: $40.75 © 2008 American Chemical Society Published on Web 01/19/2008
1012
Ind. Eng. Chem. Res., Vol. 47, No. 4, 2008
Figure 1. XRD patterns of parent R-NiMoO4 and samples reduced by CaH2 at 300 and 450 °C. Peaks marked by the symbols “9”, “g”, “O”, and “×” indicate those peaks assigned to R-NiMoO4, MoO2, Ni, and intermetallic compounds between Ni and Mo, respectively.
heptamolybdate (Merck, 99+%) and 750 mL of 0.4 M nickel nitrate (Aldrich, 99+%) in thermoregulated conditions at a temperature of 63 °C and pH 6.0.20 The purity of the prepared NiMoO4 from excess MoO3 and NiO was confirmed by Raman spectroscopy and XRD and thermal analyses (DTA/TGA). Different NiMoO4 samples were reduced using CaH2 (Aldrich, 99.9%) following the reported procedure in the literature.19,21 NiMoO4 sample was mixed and ground with CaH2 in a stoichiometric ratio in a He-filled glovebox, and then sealed in an evacuated Pyrex ampule (p < 2 × 10-4 Torr). The sealed reaction vessel was then heated for two periods of 3 days at 100 °C with intermediate grinding. The byproduct (CaO) from the reaction mixture was removed from the produced solid by washing with a solution of 1 M NH4Cl in CH3OH, in a Schlenk filter under a nitrogen atmosphere. The product solid was then further washed with CH3OH before being dried under vacuum (p < 1 × 10-1 Torr); the resulted catalyst was denoted NMH1. Other catalyst samples were reduced using CaH2 at 200, 300, and 450 °C, following the same procedure as above; the resulted catalysts were denoted as NMH2, NMH3, and NMH4, respectively. Atomic absorption (AA) spectroscopic analysis of the methanolic filtrate could not detect any Ni and Mo, which indicated that catalyst dissolution did not occur during washing processes. A reference sample (denoted as NMH2) was reduced with 5% H2/He gas mixture (40 mL/min) at 450 °C for 4 h. X-ray diffraction measurements were performed using a Philips X’Pert MPD (multipurpose X-ray diffractometer) employing Cu KR1,2 radiation (λ ) 1.5405 Å) for 2θ angles varying from 10° to 80°. The scan rate was 0.4°/min corresponding to a step size of 0.04° and a step time of 3 s. Cell dimension analysis was performed with the program Win cell 1.1. The particle size (t(Å)) of NiMoO4 was calculated by using the Scherrer formula: t(Å) ) 0.92λ/(B cos θ), where B is the width at the half-maximum of the peak at 2θ ) 28.817°. BET surface areas were measured using the surface area analyzer Quanta Chrome Nova 2200. The calcium content in the catalysts reduced by CaH2 was determined by AA on a Perkin-Elmer 3100 EDS system. Catalytic activity measurements were performed employing a conventional fixed-bed reactor system using air as the carrier gas for the cyclohexane feed. The following reaction conditions were employed: catalyst weight, 0.2 g; flow rate of air, 20 mL/ min; molar feed rate of cyclohexane, 4 × 10-3 mol/h; reaction
temperature, 200-500 °C. Analysis of reactants and products was performed by an on-line Shimadzu GC-17A with FID and TCD detectors using two columns, namely, fused silica FFAP capillary (50 m × 0.32 i.d., AD 0.46) (for cyclohexane, cyclohexene, cyclohexadiene, and benzene) and HaySep D (80/ 100) (for COx). No homogeneous gas phase for conversion of cyclohexane was observed in this temperature range. On the other hand, in other catalytic runs, temperature was adjusted for each catalyst to have cyclohexane conversion (5%), to compare selectivity for cyclohexane oxidative dehydrogenation products.22 The product yield was calculated as follows: [moles of product produced × 100]/[maximum number of moles of product that can be produced]. 3. Results and Discussion Figure 1 shows the X-ray diffraction (XRD) patterns of the parent nickel molybdate and samples reduced by CaH2 at 300 and 450 °C. The prepared nickel molybdate showed a diffraction pattern which corresponds to pure R-NiMoO4 (JCPDS standard file 33-0948). Reduction of R-NiMoO4 samples at 100 and 200 °C resulted in no observable change to the powder XRD patterns of theses samples. However, reduction of R-NiMoO4 at 300 °C (Figure 1) produced the following phases: MoO2 (JCPDS file 78-1071) and Ni (JCPDS file 04-0850). In addition, the peaks characteristic of R-NiMoO4 were also detected, which indicated that no full conversion of R-NiMoO4 occurred under these reduction conditions. Furthermore, new weak peaks of d-spacing 4.52, 3.97, 2.89, 2.86, 2.60, 2.26, 1.99, 1.78, and 1.65 Å were also detected, which are possibly referred to MoNi4 (JCPDS File Card No. 03-1036) and/or MoNi (JCPDS File Card No. 48-1745), whose characteristic lines are almost coincident. Similar phases (MoO2, Ni, R-NiMoO4, and NiMo intermetallic compounds) were detected in the XRD pattern of the sample reduced at 450 °C (Figure 1). However, the following differences were observed between the diffraction pattern recorded at 300 °C and that one recorded at 450 °C: (i) there was a significant decrease in the intensity of the peaks characteristic of incompletely reduced R-NiMoO4 (R-NiMoO4“ICR”); (ii) the peaks of R-NiMoO4 at 2θ ) 14.10°, 43.94°, and 62.20° disappeared completely; (iii) the peaks characteristic of MoO2 and Ni in the NMH4 pattern have a higher intensity than that observed in the pattern of NMH3 sample; (iv) one of the peaks
Ind. Eng. Chem. Res., Vol. 47, No. 4, 2008 1013
Figure 2. XRD patterns of R-NiMoO4 reduced by H2 at 450 °C. Peaks marked by 9 symbols indicate those peaks assigned to R-NiMoO4. Table 1. Surface Area, Detected XRD Phases, and Bulk Calcium Concentration Determined by Using Atomic Absorption Spectroscopy catalyst
SBET (m2/g)
XRD phases
Ca (wt %) (AA)
NiMoO4 NMH2 NMH3 NMH4
41.1 36.3 28.4 26.6
R-NiMoO4 R-NiMoO4 R-NiMoO4 + Ni + MoO2 + MoNi and/or MoNi4 R-NiMoO4 + Ni + MoO2 + MoNi and/or MoNi4 + Mo1.24Ni0.76
0.11 0.09
characteristic of MoNi intermetallic compounds also disappeared at 2θ ) 51.20°; (v) a new peak appeared at 2θ ) 43.05° (d spacing ) 2.09 Å), and this peak was probably due to Mo1.24Ni0.76 phase (JCPDS File Card No. 47-1129). These abovementioned observations indicate that reduction of R-NiMoO4 to MoO2, and Ni by CaH2, is more effective at 450 °C than at 300 °C. In contrast, the XRD pattern of the sample reduced by H2 at 450 °C showed only the peaks characteristic of R-NiMoO4 with a significant decrease in the intensity and broadening of these peaks (Figure 2). Catalyst surface areas, detected XRD phases, and bulk calcium concentrations are given in Table 1. In fact, no peaks due to calcium are observed in XRD patterns (Figures 1 and 2) or EDX spectra of reduced samples (NMH3 and NMH4). However, very small traces of calcium, 0.11 and 0.09 wt %, were determined by AA spectroscopy in the bulk of NMH3 catalyst and NMH4 catalyst, respectively. On the other hand, it is clear that reduction of R-NiMoO4 by either hydrogen or CaH2 produced a decrease in the surface area and this decrease is more pronounced in the case of NMH4 catalyst. Figure 3 represents the variation of cyclohexane conversion rate over catalysts under investigation with reaction temperature. It is clear that the parent R-NiMoO4 catalyst exhibited the highest activity at reaction temperatures above 300 °C, where it has a conversion rate ca. 2.0 times higher than that of the other catalysts. However, all catalysts studied were found to obey the same trend of the variation of cyclohexane conversion rate with reaction temperature; namely, the conversion rate increased with increasing temperature, attained a maximum value at ca. 450 °C, and then remained nearly constant up to 500 °C. On the other hand, catalyst samples reduced with either H2 or CaH2 afforded approximately the same conversion rate in the high-temperature range of 400-500 °C. The oxidation of cyclohexane over all the catalysts under study yielded cyclohexene, 1,3-cyclohexadiene, and benzene as
organic products as well as CO2 and CO as inorganic carbon products. The patterns of distribution of the yielded reaction products (in mole percent) over parent R-NiMoO4, NMH2, NMH3, and NMH4 catalysts as a function of reaction temperature are shown in Figure 4. The CO yield was not considered in this study because the produced amount of CO is very small for all studied catalysts. In the case of parent R-NiMoO4 (Figure 4a), benzene was the predominant product detected together with traces of cyclohexene, cyclohexadiene, and CO2 at all temperatures. The yield of benzene increased with increasing temperature and reached a maximum at about 400 °C and then decreased at 450 °C. However, with NMH2 catalyst (Figure 4b), a significant decrease in the benzene yield was observed which was accompanied by an increase in cyclohexene (mol %) at all reaction temperatures, but benzene is still the predominant product above 350 °C. On the other hand, the yield of benzene attained a maximum at about 350 °C and then remained nearly constant up to 500 °C. In contrast, with NMH3 and NMH4
Figure 3. Cyclohexane conversion rate over ([) parent R-NiMoO4, (9) R-NiMoO4 reduced by H2 at 450 °C, (2) R-NiMoO4 reduced by CaH2 at 300 °C, and (×) R-NiMoO4 reduced by CaH2 at 450 °C.
1014
Ind. Eng. Chem. Res., Vol. 47, No. 4, 2008
Figure 4. Distribution of reaction products in mol % ODH of cyclohexane over (a) parent R-NiMoO4, (b) reference sample reduced by H2 molecule at 450 °C, and (c, d) samples reduced by CaH2 anion at 300 and 450 °C, respectively, as a function of reaction temperature.
catalysts, cyclohexene was the major product detected at all reaction temperatures; benzene and CO2 were also detected in addition to cyclohexene, together with a very small trace of cyclohexadiene (Figure 4c,d). The calculated rates of cyclohexane conversion at 500 °C and selectivity of reaction products at isoconversion (5%) for all the studied catalysts are listed in Table 2. It is clear that the intrinsic rates of reduced catalysts are lower than that of pure R-NiMoO4 and followed the same trend as the rates of cyclohexane conversion based on unity weight. Such behavior can indicate that the observed decrease in cyclohexane conversion of R-NiMoO4 by reduction with either H2 or CaH2 is not only due to the observed decrease in surface area. In addition, there is an increase in reaction temperature (T(5%)) required to keep cyclohexane conversion constant at 5% for all reduced catalysts. This increase may be due to the fact that high temperature is necessary to compensate the loss in activity of R-NiMoO4 by reduction. As can be also seen in Table 2, at isoconversion (5%), the parent R-NiMoO4 exhibited the highest selectivity toward benzene. However, NMH4 catalyst is the most selective toward cyclohexene, but at a higher reaction temperature (T(5%)) than that of NMH3. These above results confirmed that reduction of R-NiMoO4 by CaH2 leads to significant modifications in catalytic performance. As already observed, both NMH3 and NMH4 catalysts have lower cyclohexane conversion than the parent R-NiMoO4. According to the XRD results in Figure 1, new phases (MoO2, Ni, intermetallic compounds of different Mo/Ni ratios) were detected in NMH3 and NMH4 catalyst patterns together with R-NiMoO4“ICR”. This may indicate that these new phases are inactive. However, the high selectivity of these catalysts toward cyclohexane might be affected by the presence of these phases. It seems that there is a synergetic effect between theses phases and R-NiMoO4“ICR”, but the exact role of these phases cannot be stated on the basis of this work. On the other hand, significant modifications were observed in the crystal structure “cell dimensions” of R-NiMoO4“ICR” phase founded in NMH3 and NHM4 catalysts (Table 3). There is an expansion in the b- and c-axes, and a simultaneous contraction of the a-axis was observed. This was accompanied by an increase in the R-NiMoO4 particle size. Such behavior can be expected in the R-to-β-NiMoO4 phase transition induced by a change in temperature. However, these modifications are completely different from that observed in the above-mentioned transition.23,24 The obtained modifications in cell dimensions of R-NiMoO4 after reduction by CaH2 may reflect a change in the coordination of Mo, namely, a possible “metastable coordination”. This phenomenon can give an explanation for the observed high selectivity of these catalysts toward cyclohexene. According to the mechanism proposed by Patcas et al.,25 for the gas-phase oxidation of cyclohexane on metal oxides, cyclohexene is a primary product and undergoes consecutive transformations to cyclohexadiene and benzene. Therefore, it seems that, in the case of pure R-NiMoO4 catalyst, cyclohexane and intermediate oxide hydrogenation products are interacting strongly with catalyst and are easily over oxide hydrogenated to benzene. However, with NMH3 and NHM4 catalysts, cyclohexene might be desorbed easier from the surface. This could be due to reduction by CaH2 modifying the nature of the adsorption centers. In this way, we can suggest that, in the cases of the NMH3 and NHM4 catalysts, the proposed modification in the nature of the adsorption centers would be related to the observed changes in the R-NiMoO4 molecular structure “cell dimensions”. It is important to mention that no significant
Ind. Eng. Chem. Res., Vol. 47, No. 4, 2008 1015 Table 2. Catalytic Results in Cyclohexane Oxidative Dehydrogenation over r-NiMoO4 and Samples Reduced by either H2 or CaH2a catalyst
rcyclohexaneb (mol/h/g) × 103
intrinsic ratec (mol/h/m2) × 103
S(C6H6)d (%)
S(C6H8+C6H10)e (%)
T(5%)f (°C)
R-NiMoO4 NMH2 NMH3 NMH4
8.9 4.0 4.3 4.5
4.3 2.2 3.0 3.4
74 68 31.7 28
25.8 29.3 50.6 52.1
273 292 282 296
a Cyclohexane molar feed rate 4 × 10-3 mol/h and W ) 0.2 g. b Rates of cyclohexane conversion based on unity weight at 500 °C. c Rates of cyclohexane conversion based on unity surface area at 500 °C. d Selectivity to benzene at conversion level of 5%. e Selectivity to cyclohexene and cyclohexadiene at conversion level of 5%. f Temperature at which the cyclohexane conversion is 5%.
Table 3. Calculated Cell Dimensions and Particle Size of Parent r-NiMoO4 Before Reduction and After Reduction with CaH2 at Different Temperaturesa
a
catalyst
a [Å]
b [Å]
c [Å]
β (deg)
t (Å)
parent R-NiMoO4 NMH3 NMH4
9.5741 8.9716 9.0917
8.7440 9.4902 9.4502
7.6552 8.7932 8.7344
114.136 102.231 102.621
213.5 345.2 334.8
The estimated cell dimensions of the parent R-NiMoO4 are very close to those reported for R-phase in ref 23.
modifications were observed in the estimated lattice parameter “cell dimension” of R-NiMoO4 sample reduced by H2. Furthermore, one cannot exclude that the catalytic performance of NMH3 and NMH4 catalysts might also be affected by the presence of trace amounts of calcium from the hydride precursor. As mentioned above, the presence of calcium (0.090.11 wt %) in these catalysts was confirmed by atomic absorption analysis (Table 1). The Ca issue is outside the scope of this article; however, some conclusions can be drawn on the basis of literature results. It has been reported that Ca modified the catalytic performance of R-NiMoO4 in the oxidative dehydrogenation of propane to propene.22 Nevertheless, high percentages of calcium are required (1-2 wt %). The above interpretation suggests that Ca does not play a decisive role in determining the selectivity of NMH3 and NMH4 catalysts toward cyclohexene. The outcomes of the reaction of R-NiMoO4 with CaH2 are completely different than that obtained with H2. This may be due to the differences between the two processes in both the nature of the reducing species and the reaction pathways. CaH2 thermally decomposes at 880 °C; therefore mainly H- may be present as reducing agent at the temperatures used (300 and 450 °C).19,26 Hayward et al. reported that reduction of metal oxides by H- produced metal oxide hydrides. Thus, in this sense, we can envisage that, during reduction with CaH2, nickel molybdenum oxide hydride (NiMoO4-xHx) may be formed as an intermediate of specific molybdenum coordination.19 The changes observed in the cell dimensions of the R-NiMoO4“ICR” may give an induction about the possibility of formation of this intermediate. The proposed intermediate may be converted consecutively to the detected intermetallic phases through disproportionation reaction with CaO.19 4. Conclusions Catalytic results discussed above showed that reduction of R-NiMoO4 with CaH2 leads to lower activity for cyclohexane conversion but gives higher oxidative dehydrogenation selectivity toward cyclohexene. The significant high selectivity of this catalyst toward cyclohexene was due to reduction by CaH2 modified molybdenum coordination. Calcium hydride allows the reduction of R-NiMoO4 to crystalline Ni and MoO2 at 300 °C, where H2 is not effective. CaH2 apparently affords hydride anion as a reducing species at the reduction temperatures used. Formation of intermediate nickel molybdenum oxide hydride was proposed. To clarify this hypothesis, further specific characterization studies are still required; these are beyond the
scope of the present work. Further investigations are necessary to determine precisely the most optimum reduction conditions to avoid conversion of a large number of R-NiMoO4 molecules to the above-mentioned phases. Acknowledgment The authors gratefully acknowledge the Deanship of Scientific Research, King Faisal University, Saudi Arabia, for financial support (Project No. 7051). Literature Cited (1) Delmon, B. The Boiling Pot at Oxide Surfaces. Catal. Today 2006, 117, 69. (2) Dury, F; Gaigneaux, E. M.; Ruiz, P. The Active role of CO2 at Low Temperature in Oxidation Processes: The Case of the Oxidative Dehydrogenation of Propane on NiMoO4 Catalysts. Appl. Catal., A 2003, 242, 187. (3) Dury, F.; Centeno, M. A.; Gaigneaux, E. M.; Ruiz, P. An Attempt to Explain the Role of CO2 and N2O as Gas Dopes in the Feed in the Oxidative Dehydrogenation of Propane. Catal. Today 2003, 81, 95. (4) Dury, F.; Centeno, M. A.; Gaigneaux, E. M.; Ruiz, P. Interaction of N2O (as gas dope) with Nickel Molybdate Catalysts During the Oxidative Dehydrogenation of Propane to Propylene. Appl. Catal., A 2003, 247, 231. (5) Cellier, C.; Blangy, B.; Mateos-Pedrero, C.; Ruiz, P. Modification of Catalytic Performances Due to the Co-feeding of Hydrogen or Carbon Dioxide in the Partial Oxidation of Methane over a NiO/γ-Al2O3 Catalyst. Catal. Today 2006, 112, 112. (6) Demoluin, O.; Seunier, I.; Dury, F.; Navez, M.; Rachwalik, R.; Sulikowski, B.; Gonzalez-Carrazan, S. R.; Gaigneaux, E. M.; Ruiz, P. Modulation of Selective Sites by Introduction of N2O, CO2 and H2 as Gaseous Promoters into the Feed during Oxidation Reactions. Catal. Today 2005, 99, 217. (7) Maderia, L. M.; Portela, F. M. Nickel Molybdate Catalysts and their Use in the Selective Oxidation of Hydrocarbons. Catal. ReV.sSci. Eng. 2002, 44, 247. (8) Zaˇvoianu, R.; Dias, C. R.; Soares, A. P. V.; Portela, M. F.; Oxidative dehydrogenation of i-butane over nanostructured silica-supported NiMoO4 catalysts with low content of active phase. Appl. Catal., A 2006, 298, 40. (9) AbdelDayem, H. M.; Ruiz, P. Enhancement of the Catalytic Performance of NiMoO4 and Modification of the Kinetic Parameters of Oxidative Dehydrogenation of Propane over NiMoO4/Sb2O4 Biphasic Catalyst by Oxygen Spillover. Stud. Surf. Sci. Catal. 2001, 138, 363. (10) Kaddouri, A.; Anouchinsky, R.; Mazzochcia, C.; Madeira, L.; Portela, M. F. Oxidative Dehydrogenation of Ethane on the R and β Phases of NiMoO4. Catal. Today 1998, 40, 201. (11) Mazzochia, C.; Abourmad, C.; Diagne, C.; Tempesti, E.; Hermann, J. M.; Thom, J. M. On the NiMoO4 oxidative dehydrogenation of propane to propene: some physical correlations with the catalytic activity Catal. Lett. 1991, 10, 181. (12) Mederia, L. M.; Portela, M.; Mazzochia, C.; Anouchinsky, A. R. Reducibility of Undoped and Cs-doped R-NiMoO4 Catalysts: Kinetic Effects in the Oxidative Dehydrogenation of n-Butane. Catal. Today 1998, 40, 229.
1016
Ind. Eng. Chem. Res., Vol. 47, No. 4, 2008
(13) AbdelDayem, H. M. Dynamic Phenomena during Reduction R-NiMoO4 in Different Atmospheres: In situ Thermo-Raman Spectroscopy Study. Ind. Eng. Chem. Res. 2007, 46, 2467. (14) Shriver, D. F.; Atkins, P. W. Inorganic Chemistry; 3rd ed.; W. H. Freeman: New York, 1999; pp 253-255. (15) Sokolov, V. V.; Osadchaya, L. I.; Galkin, P. S.; Zelenin, J. M.; Stonoga, J. A.; Zubareva, A. P. Synthesis of Intermetallic Compounds by Using Lithium Hydride. J. Rare Earths 2002, 20, 256. (16) Hayward, M. A.; Rosseinsky, M. J. Synthesis of the Infinite Layer Ni(I) Phase NdNiO2+x by the Low Temperature Reduction of NdNiO3 with Sodium Hydride. Solid State Sci. 2003, 5, 839. (17) Martinez-Lope, M. J.; Casais, M. T.; Alonso, J. A. Stabilization of Ni+ in Defect Perovskites La(Ni1-xAlx)O2+ x with ‘Infinite-Layer’ Structure. J. Alloys Compd. 1998, 277, 109. (18) Murphy, D. W.; Zahurak, S. M.; Vyas, B.; Thomas, M.;. Badding, M. E; Fang, W. C; A New Route to Metal Hydrides. Chem. Mater. 1993, 5, 767. (19) Hayward, M. A.; Cussen, E. J.; Claridge, J. B.; Bieringer, M.; Rosseinsky, M. J.; Kiely, C. J.; Blundell, S. J.; Marshall, I. M.; Pratt, F. L. The Hydride Anion in an Extended Transition Metal Oxide Arrays LaSrCoO3H0.7. Science 2002, 295, 1882. (20) Ozkan, U. S.; Scharder, G. L. NiMoO4 Selective Oxidation Catalysts Containing Excess MoO3 for the Conversion of C4 Hydrocarbons to Maleic Anhydride: I. Preparation and Characterization. J. Catal. 1985, 95, 120.
(21) Hayward, M. A.; Green, M. A.; Rosseinsky, M. J.; Sloan, J. Sodium Hydride as a Powerful Reducing Agent for Topotactic Oxide Deintercalation: Synthesis and Characterization of the Nickel(I) Oxide LaNiO2. J. Am. Chem. Soc. 1999, 121, 8843. (22) Kaddouri, A.; Mazzocchia, C.; Tempsti, E. Propane and Isobutane Oxidative Dehydrogenation with K, Ca and P-doped R-, and β-Nickel Molybdate Catalysts. Appl. Catal., A 1998, 169, L3. (23) Sleight, A. W.; Chamberland, B. L. Transition Metal Molybdates of the Types AMoO4. Inorg. Chem. 1968, 8, 1672. (24) Rodriguez, J. A.; Hanson, J. C.; Chaturvedi, S. Phase Transformations and Electronic Properties in Mixed-Metal Oxides: Experimental and Theoretical Studies on the Behavior of NiMoO4 and MgMoO4. J. Chem. Phys. 2000, 112, 935. (25) Patcas, F.; Patcas, F. C. Reaction Pathways and Kinetics of the Gas-Phase Oxidation of Cyclohexane on NiO/γ-Al2O3 Catalyst. Catal. Today 2006, 117, 253. (26) Tsurov, M. A.; Afanasiev, P. V.; Lunin, V. V. Composition and Catalytic Properties of Products from the Reduction of NiMoO4. Appl. Catal., A 1993, 105, 205.
ReceiVed for reView June 8, 2007 ReVised manuscript receiVed October 28, 2007 Accepted November 8, 2007 IE070793Z
