Temperature-programmed Desorption Results Research Articles

Liquid-phase catalytic oxidation of p-chlorotoluene to p-chlorobenzaldehyde over manganese oxide octahedral molecular sieves

Manganese oxide octahedral molecular sieves (OMS-2) show much higher catalytic activities in the liquid-phase catalytic oxidation of p-chlorotoluene than MnO2, Mn3O4, Mn(OAc)2 as well as than some other transition metal oxides such as Co2O3, V2O5 and Fe2O3. Based on temperature-programmed desorption and thermogravimetric results, it is deduced that the catalytic activity of OMS-2 can be ascribed to the abundance and mobility of lattice oxygen. We investigated the effects of reaction temperature, reaction time, catalyst amount, and initial water amount on the reaction. Under optimal reaction conditions, p-chlorotoluene conversion and p-chlorobenzaldehyde selectivity are respectively 86.0% and 68.7%. The catalysts can be easily recovered by centrifugation, and reused. According to the results of X-ray diffraction and N2 adsorption/desorption analyses, there is no significant change in major characteristics of the catalyst after 4 cycles of reaction.

Synthesis and advanced dehydrogenation properties of niobium-based ammine borohydride

In this paper, niobium-based ammine borohydride has been synthesized via a simple ball milling of NbCl5·5NH3 and MBH4 (M=Li, Na) with a molar ratio of 1:5. Thermogravimetric analysis–mass spectrometry (TGA–MS) and temperature-programmed-desorption (TPD) results revealed that the dehydrogenation of NbCl5·5NH3/5LiBH4 and NbCl5·5NH3/5NaBH4 mixtures showed a two-step decomposition process with a total of 8.1wt.% and 11.2wt.% pure hydrogen evolution upon heating to 250°C, respectively. Isothermal TPD results showed that over 6wt.% and 10.4wt.% pure hydrogen were liberated from NbCl5·5NH3/5NaBH4 within 60min at 150°C and 220°C, respectively. Fourier transform infrared spectroscopy (FTIR) and isotope tagging measurements demonstrated that the dehydrogenation mechanism of niobium-based ammine borohydride is not only based on the combination reaction of BH and NH groups, but the BH⋯HB and NH⋯HN homo-polar interactions also contribute to the H2 formation.

Ceria added Sb-V2O5/TiO2 catalysts for low temperature NH3 SCR: Physico-chemical properties and catalytic activity

A systematic investigation of the effect of ceria loading over Sb-V2O5/TiO2 catalysts was carried out for the selective catalytic reduction (SCR) of NOx by NH3. The various ceria loaded Sb-V2O5/TiO2 catalysts were prepared by deposition precipitation and impregnation methods. Addition of 10% ceria to Sb-V2O5/TiO2 catalyst significantly enhanced the NOx conversion at wide temperature range of 220–500°C. The 10% ceria loaded Sb-V2O5/TiO2 catalyst showed superior N2 selectivity (>95%) throughout the reaction temperatures. The physicochemical characteristics of the obtained catalysts were thoroughly characterized by BET surface area, X-ray diffractometry (XRD), temperature programmed desorption (TPD) of NO, SO2 and NH3, H2- temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The XRD results indicated the active components of antimony and vanadia were homogeneously dispersed over CeO2/TiO2. It was found that the addition of 10% ceria to Sb-V2O5/TiO2 could enhance the total acidity and redox properties of the catalyst, which lead to show higher NOx conversions at wide temperature window. In XPS studies, increase in intensity of the chemisorbed mobile oxygen peak was observed for ceria loaded catalysts. In particular, the DRIFT spectra of ceria loaded Sb-V2O5/TiO2 catalysts showed abundant Brønsted acid sites at 1436 and 1673cm−1 band, which are responsible for high NOx conversion. Furthermore, the results of NO and SO2 TPD of 10% ceria loaded Sb-V2O5/TiO2 catalyst showed enhancement of NO adsorption and SO2 inhibition properties, which is thought to play a significant role in long term stability of the catalyst during SO2 on–off study for 38h at 240°C.

Effect of K loadings on nitrate formation/decomposition and on NOx storage performance of K-based NOx storage-reduction catalysts

We have investigated the effect of K loadings on the formation and the decomposition of KNO3 over K2O/Al2O3, and measured NOx storage performance of Pt–K2O/Al2O3 catalysts with various potassium loadings. After NO2 adsorption on K2O/Al2O3 at room temperature, ionic and bidentate nitrates were observed by Fourier transform infra-red (FTIR) spectroscopy. The ratio of the former to the latter species increased with increasing potassium loading up to 10wt%, and then stayed almost constant with additional K, demonstrating a clear dependence of loading on potassium nitrate formed. Although both K2O(10)/Al2O3 and K2O(20)/Al2O3 samples formed similar nitrate species identified by FTIR obtained after NO2 adsorption, the latter has more thermally stable nitrate species as evidenced by FTIR and NO2 temperature programmed desorption (TPD) results. With regard to NOx storage-reduction performance of Pt–K2O/Al2O3 samples, the temperature of maximum NOx uptake (Tmax) is 573K up to a potassium loading of 10wt%. As the potassium loading increases from 10wt% to 20wt%, Tmax shifted from 573K to 723K. Moreover, the amount of NO uptake (38cm3 NOx/gram of catalyst) at Tmax increased more than three times, indicating that efficiency of K in storing NOx is enhanced significantly at higher temperature, in good agreement with the NO2 TPD and FTIR results. Thus, a combination of characterization and NOx storage performance results demonstrates an unexpected effect of potassium loading on nitrate formation and decomposition processes; results important for developing Pt–K2O/Al2O3 as potential catalysts as high temperature NOx storage-reduction applications.

The release of trapped gases from amorphous solid water films. I. “Top-down” crystallization-induced crack propagation probed using the molecular volcano

In this (Paper I) and the companion paper (Paper II; R. May, R. Smith, and B. Kay, J. Chem. Phys. 138, 104502 (2013)), we investigate the mechanisms for the release of trapped gases from underneath amorphous solid water (ASW) films. In prior work, we reported the episodic release of trapped gases in concert with the crystallization of ASW, a phenomenon that we termed the "molecular volcano." The observed abrupt desorption is due to the formation of cracks that span the film to form a connected pathway for release. In this paper, we utilize the "molecular volcano" desorption peak to characterize the formation of crystallization-induced cracks. We find that the crack length distribution is independent of the trapped gas (Ar, Kr, Xe, CH4, N2, O2, or CO). Selective placement of the inert gas layer is used to show that cracks form near the top of the film and propagate downward into the film. Isothermal experiments reveal that, after some induction time, cracks propagate linearly in time with an Arrhenius dependent velocity corresponding to an activation energy of 54 kJ∕mol. This value is consistent with the crystallization growth rates reported by others and establishes a direct connection between crystallization growth rate and the crack propagation rate. A two-step model in which nucleation and crystallization occurs in an induction zone near the top of the film followed by the propagation of a crystallization∕crack front into the film is in good agreement with the temperature programmed desorption results.

An investigation on the hydrogen storage properties and reaction mechanism of the destabilized MgH2–Na3AlH6 (4:1) system

A novel hydrogen storage composite system, MgH2–Na3AlH6 (4:1), was prepared by mechanochemical milling, and its hydrogen storage properties and reaction mechanism were studied. Temperature-programmed desorption results showed that a mutual destabilization effect exists between the components. First, Na3AlH6 reacts with MgH2 to form a perovskite-type hydride, NaMgH3, Al, and H2 at a temperature of about 170 °C, which is about 55 °C lower than the decomposition temperature of as-milled Na3AlH6. Then, at a temperature of about 275 °C, the as-formed Al can destabilize MgH2 to form the intermetallic compound Mg17Al12, which is accompanied by the self-decomposition of the residual MgH2. This temperature is about 55 °C lower than the decomposition temperature for as-milled MgH2. Furthermore, when heated up to 345 °C, NaMgH3 starts to decompose into NaH, Mg, and H2, which is followed by the decomposition of NaH at a temperature of about 370 °C. Rehydrogenation processes show that Mg17Al12 and NaMgH3 are fully reversible. It is believed that the Mg17Al12 and NaMgH3 formed in situ provide synergetic thermodynamic and kinetic destabilization, leading to the dehydrogenation of MgH2, which is responsible for the distinct reduction in the operating temperatures of the as-prepared MgH2–Na3AlH6 (4:1) composite system.

Flower-Like Co-Ni/C Bimetallic Catalysts for the Selective Hydrogenation of o-Chloronitrobenzene

Three dimensional flower-like Co-Ni/C bimetallic catalysts composed of interlaced carbon flakes with highly dispersed metal nanoparticles were synthesized by a facile hydrothermal/solvothermal process followed by a heat treatment in flowing N 2 . The sizes of the metal nanoparticles were from 26 to 4 nm, which became smaller as the Co/Ni molar ratio increased. The catalytic activities for the selective hydrogenation of o -chloronitrobenzene to o -chloroaniline were tested. The conversion of o -chloronitrobenzene over the bimetallic Co-Ni/C catalysts was increased by up to 200% compared with that over a mono-metallic Co/C catalyst, which was due to a synergistic interaction between the Co and Ni species. Hydrogen temperature-programmed desorption results showed that new active sites were formed in the Co 50 Ni 50 /C catalyst due to the formation of a Co-Ni alloy, which gave the improved activity of the Co 50 Ni 50 /C catalyst. 采用简单的水热/溶剂热法, 经后续在氮气气氛中的热处理合成了三维花型 Co-Ni/C 双金属催化剂, 它由交织炭片构成, 金属纳米颗粒高度分散其中. 随着 Co/Ni 摩尔比的增加, 金属颗粒的粒径逐渐从 26 nm 减至 4 nm 左右. 将该催化剂用于邻氯硝基苯选择性加氢制备邻氯苯胺反应, 其催化活性最高为单金属催化活性的 2 倍. 这是由于 Co 和 Ni 物种之间存在协同效应. 氢气程序升温脱附结果显示, Co/Ni 合金的生成使得 Co 50 Ni 50 /C 催化剂产生了新的催化活性位, 因而其活性显著提高. Three dimensional flower-like Co-Ni/C catalysts composed of interlaced nanoflakes with highly dispersed metal nanoparticles gave better activity for the selective hydrogenation of o -chloronitrobenzene because of a synergistic interaction between Co and Ni.

Alumina Grafted to SBA-15 in Supercritical CO2 as a Support of Cobalt for Fischer–Tropsch Synthesis

The impact of acidity and pore size on the activity and product selectivity of the Fischer–Tropsch (FT) synthesis was comparatively investigated over cobalt supported on a series of alumina-grafted siliceous SBA-15 (Al-SBA-15) via the post-synthesis method in the medium of supercritical CO2. X-ray diffraction (XRD) results indicate that the ordered mesoporous structure of SBA-15 is preserved after grafting different amounts of alumina. However, both the Brunauer–Emmett–Teller (BET) surface area and the pore volume of Al-SAB-15 are decreased with an increasing content of alumina. Ammonia temperature-programmed desorption (NH3-TPD) results indicate that the acidity of Al-SBA-15, which is dominantly contributed by weak acidic sites, increases continuously with an increasing content of alumina. The 20 wt % Co-supported catalysts prepared by the incipient impregnation method were evaluated for FT synthesis in a fixed-bed reactor under the conditions of 1.0 MPa, 235 °C, H2/CO = 2, and W/F = 5.02 g h mol–1. Sign...

Quantitative Studies on the Oxygen and Nitrogen Functionalization of Carbon Nanotubes Performed in the Gas Phase

Gas-phase methods were applied for the oxygen and nitrogen functionalization of multiwalled carbon nanotubes (CNTs). The oxygen functionalization was performed by HNO3 vapor treatment at temperatures from 200 to 250 °C for 12 h up to 120 h. The oxygen-functionalized CNTs were used as the starting material for nitrogen functionalization through thermal treatment under NH3. The BET surface area increased after the treatment in HNO3 vapor, which also caused the weight loss due to carbon corrosion. The oxygen content increased with increasing treatment time but decreased with increasing temperature, as disclosed by elemental analysis, X-ray photoelectron spectroscopy, and temperature-programmed desorption (TPD) results. The surface acidity increased with increasing treatment time as shown by TPD using NH3 as a probe molecule. As to nitrogen functionalization, the amount of nitrogen was correlated with the oxygen amount in the starting CNTs. A higher NH3 concentration caused a lower BET surface area due to carbon corrosion. The incorporation of both oxygen and nitrogen lowered the thermal resistance of CNTs. The nitrogen-functionalized CNTs showed only a slight decrease, in contrast to a significant decrease observed for O-functionalized CNTs. The formation or removal of coordinatively unsaturated carbon like amorphous carbon or defects was found to be involved in all of the functionalization, desorption, and oxidation processes.

Modified zeolite catalyst for selective dialkylation of naphthalene

The dialkylation of naphthalene with isopropanol to produce 2,6-diisopropylnaphthalene (2,6-DIPN) was carried out over HY zeolite. The effects of various reaction conditions, such as pressure, temperature, space velocity, molar ratio of alcohol to naphthalene and time on stream (TOS) on product distribution were studied. HY zeolite was modified by transition metals, such as Fe3+, Ni2+, Co2+ and Cu2+ using wet impregnation method to maximize the selectivity to 2,6-DIPN. The catalysts were characterized by XRF, XRD, TGA, nitrogen adsorption–desorption and Temperature Programmed Desorption (TPD) of t-Butylamine. Under optimum reaction conditions, (50bar, 220°C, isopropanol/naphthalene=4 (mole ratio), WHSV=18.8h−1, TOS 6h), HY zeolite modified by Fe3+ was found to give the highest selectivity, by increasing the 2,6/2,7-DIPN ratio from 2.8 to 6.6. The experimental results indicate that the selectivity to 2,6-DIPN is in the order of Fe–HY>Ni–HY>Cu–HY>Co–HY>HY. Naphthalene conversion of 77% was obtained over HY zeolite, while after modification by Fe, Co, Ni and Cu, the conversion was changed to 73%, 76%, 88% and 96%, respectively. TPD result indicates different distribution of weak, medium and strong acid sites in the modified catalysts. TGA analysis of used catalyst samples revealed that a higher amount of PIPN was produced on zeolite modified by Co and Cu. This confirms that PIPN molecules are possible coke precursors, and therefore led to larger amount of coking on the Co–HY and Cu–HY catalysts.

Adsorption and thermal decomposition of 2-octylthieno[3,4-b]thiophene on Au(1 1 1)

The adsorption and thermal stability of 2-octylthieno[3,4-b]thiophene (OTTP) on the Au(111) surfaces have been studied using scanning tunneling microscopy (STM), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). UHV-STM studies revealed that the vapor-deposited OTTP on Au(111) generated disordered adlayers with monolayer thickness even at saturation coverage. XPS and TPD studies indicated that OTTP molecules on Au(111) are stable up to 450K and further heating of the sample resulted in thermal decomposition to produce H2 and H2S via C–S bond scission in the thieno-thiophene rings. Dehydrogenation continues to occur above 600K and the molecules were ultimately transformed to carbon clusters at 900K. Highly resolved air-STM images showed that OTTP adlayers on Au(111) prepared from solution are composed of a well-ordered and low-coverage phase where the molecules lie flat on the surface, which can be assigned as a (9×2√33)R5° structure. Finally, based on analysis of STM, TPD, and XPS results, we propose a thermal decomposition mechanism of OTTP on Au(111) as a function of annealing temperature.

Depletion of monolayer liquid lubricant films induced by high-frequency pulsed-laser heating in thermally assisted magnetic recording

In this study, lubricant depletion due to high-frequency pulsed-laser heating was investigated for lubricant films with thicknesses of both more than and less than one monolayer. A conventional lubricant, Zdol2000, was used. It was found that the critical temperature at which the lubricant begins to deplete owing to laser heating was strongly dependent on the lubricant film thickness. In the case in which the thickness of the lubricant film was less than one monolayer, this temperature was approximately 170 °C higher than it was when the thickness was more than one monolayer. To analyze the lubricant depletion mechanism, we examined the tested lubricant film using temperature programmed desorption (TPD) spectroscopy. It was found that the lubricant depletion characteristics due to laser heating could be explained using the experimental TPD results for the tested lubricant film, and that the depletion mechanism involves the desorption or decomposition of the lubricant molecules, which interact with the diamond-like carbon thin films when the lubricant film thickness is less than one monolayer. Further, the results of TPD and of a thermogravimetric analysis (TGA) of the lubricant were compared. The thermal robustness of the ultra-thin liquid lubricant films was found to be greater than that of the bulk lubricant materials.

Depletion of Monolayer Liquid Lubricant Films Induced by Laser Heating in Thermally Assisted Magnetic Recording

In this study, lubricant depletion due to high-frequency pulsed-laser heating, with a heating rate of ~108–109 K/s, was investigated for lubricant films with thicknesses of greater than and less than one monolayer. The conventional lubricants, Zdol2000 and Ztetraol2000, were used. It was found that the critical temperature at which the lubricants begin to deplete was strongly dependent on the lubricant film thickness. For lubricant film thicknesses of less than one monolayer, this temperature was approximately 170 °C higher than that for thicknesses of greater than one monolayer. To analyze the lubricant depletion mechanism, we examined the tested lubricant films, using temperature-programmed desorption (TPD) spectroscopy, in which the heating rate was 0.3 K/s. It was found that the lubricant depletion characteristics could be explained using the experimental TPD results for the tested lubricant films. The depletion mechanism involves the desorption or decomposition of the lubricant molecules, which interact with the diamond-like carbon thin films when the lubricant film thickness is less than one monolayer. Therefore, we concluded that the TPD results were highly effective for evaluating the lubricant depletion characteristics induced by rapid laser heating, even though the heating rates are substantially different.

Glucose production from hydrolysis of cellulose over a novel silica catalyst under hydrothermal conditions

A novel silica catalyst was synthesized by evaporation-induced self-assembly (EISA) method and tested for the catalytic selective hydrolysis of cellulose to glucose. This silica catalyst exhibited a higher catalytic activity than other oxides prepared by the same method, such as ZrO2, TiO2, and Al2O3. Using silica as a catalyst, cellulose was selectively hydrolyzed into glucose with a glucose yield as high as 50% under hydrothermal conditions without hydrogen gas. The silica catalyst was characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results of temperature-programmed desorption of ammonia (NH3-TPD) and textural properties indicated that the synergistic effect between strong acidity and a suitable pore diameter of the silica catalyst may be responsible for its high activity. In addition, the catalyst was recyclable and showed excellent stability during the recycle catalytic runs.

Chemical and microscopic analysis of graphene prepared by different reduction degrees of graphene oxide

Chemical reduction of exfoliated graphite oxide (graphene oxide) has become one of the most promising routes for the mass production of graphene sheets. Nonetheless, the material obtained by this method exhibits considerable structural disorder and residual oxygen groups, and reports on their microscopic structure are quite scarce. We have investigated the structure and chemistry of graphene oxide samples reduced to different degrees using atomic force and scanning tunneling microscopy (AFM/STM) as well as X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD), respectively. TPD and XPS results indicate that reduction proceeds mainly by eliminating the most labile oxygen groups, which are ascribed to epoxides and hydroxyls on basal positions of the graphene plane. AFM/STM shows that the sheets are composed of buckled oxidized regions intermingled with flatter, non-oxidized ones, with the relative area of the latter increasing with the reduction degree.

Effect of original activated carbon support and the presence of NOx on CO oxidation over supported Wacker-type catalysts

The supported Wacker-type catalysts were prepared with different original activated carbons (wood, coconut shell and coal based carbon) as supports, and the catalytic activities for CO oxidation with or without NOx were investigated. Nitrogen adsorption, temperature-programmed desorption (TPD) and Boehm titration results showed that wood based activated carbon had developed meso-/macropore structure and rich oxygen functional groups. Oxygen-containing surface groups benefited active sites Pd2+ and Cu2+ phase enriched on the catalyst surface which were confirmed by X-ray Photoelectron Spectroscopy (XPS). H2 temperature-programmed reduction (H2-TPR) experiments indicated that the oxygen-containing surface groups increased the ratio of copper species adjacent to palladium species and promoted the reducibility of Cu2+ species. Density functional theory (DFT) calculation displayed that NOx was more active to combine with Pd2+ component than CO did, which explained the presence of NOx had an obvious inhibition effect on CO oxidation.

Oxidative dehydrogenation of n-butenes to 1,3-butadiene over BiMoFe0.65P x catalysts: effect of phosphorous contents

A series of BiMoFe0.65P x oxide catalysts with varying phosphorous contents from 0.0 to 0.6 mol ratio were prepared by a co-precipitation method, and oxidative dehydrogenation (ODH) was carried out to produce 1,3-butadiene (BD) from n-butenes. The physico-chemical properties of the oxide catalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, N2 sorption, and NH3 and 1-butene temperature-programmed desorption (TPD). Among the catalysts studied here, BiMoFe0.65P0.1 oxide catalyst showed the highest conversion and selectivity to BD. From the result of 1-butene TPD, the higher catalytic activity is related to the amount of weakly bounded intermediate and the desorbing temperature of strongly bounded intermediates. Also, the higher catalytic activity likely originates from the acidity of the BiMoFe0.65P0.1 oxide catalyst; its acidity was higher than that of phosphorous-free oxide catalyst and further contained other oxide catalysts. BiMoFe0.65P0.1 oxide catalyst is stable and no significant deactivation for 100 h ODH reaction was shown.

Adsorption and Reaction of Furfural and Furfuryl Alcohol on Pd(111): Unique Reaction Pathways for Multifunctional Reagents

Surface chemical reactions of highly functional biomass derivatives such as furans with oxygenated ligands are often considered in terms of the chemistry of their individual functional groups, with little focus on how multifunctionality affects surface chemistry. To probe these effects on functionalized furans, temperature-programmed desorption (TPD) experiments and density functional theory (DFT) calculations were used to study the thermal chemistry of furfural, C4H3(CHO)O, and furfuryl alcohol, C4H3(CH2OH)O on Pd(111). The TPD results indicate that furfural undergoes decomposition to produce furan, propylene, carbon monoxide, and hydrogen. Furfuryl alcohol forms the same products but also undergoes an unexpected C–O scission process that yields methylfuran and water. Together with DFT calculations, these results indicate that furfuryl alcohol can decompose through a surface furfural intermediate, similar to the reaction pathway observed for simple alcohols such as ethanol. The additional methylfuran pat...

Crystallization Kinetics and Excess Free Energy of H2O and D2O Nanoscale Films of Amorphous Solid Water

Temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) are used to investigate the crystallization kinetics and measure the excess free energy of metastable amorphous solid water films (ASW) of H(2)O and D(2)O grown using molecular beams. The desorption rates from the amorphous and crystalline phases of ASW are distinct, and as such, crystallization manifests can be observed in the TPD spectrum. The crystallization kinetics were studied by varying the TPD heating rate from 0.001 to 3 K/s. A coupled desorption-crystallization kinetic model accurately simulates the desorption spectra and accurately predicts the observed temperature shifts in the crystallization. Isothermal crystallization studies using RAIRS are in agreement with the TPD results. Furthermore, highly sensitive measurements of the desorption rates were used to determine the excess free energy of ASW near 150 K. The excess entropy obtained from these data is consistent with there being a thermodynamic continuity between ASW and supercooled liquid water.

Effect of different additives on the hydrogen storage properties of the MgH2-LiAlH4 destabilized system

The hydrogen storage properties of the MgH2-LiAlH4 (4 : 1) composite system with and without additives were studied. 5 wt.% of TiF3, NbF5, NiF2, CrF2, YF3, TiCl3·1/3AlCl3, HfCl4, LaCl3, CeCl3, and NdCl3, respectively, was added to the MgH2-LiAlH4 (4 : 1) mixture, and their catalytic effect was investigated. Temperature programmed desorption results show that addition of metal halides to the MgH2-LiAlH4 (4 : 1) composite system improves the onset desorption temperature. The hydrogen desorption properties of metal halide-doped MgH2-LiAlH4 (4 : 1) composites were also improved as compared to the undoped MgH2-LiAlH4 (4 : 1) composite. Furthermore, the activation energy and the change in enthalpy in the doped and undoped composite were measured by differential scanning calorimetry. In addition, the reaction pathway of the MgH2-LiAlH4 (4 : 1) composite system and the mechanisms that work in this composite during the de/re-hydrogenation process were determined by X-ray diffraction.