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In this work, we disclosed that diphenyl oxalate serves as a CO surrogate to enable a Ni-catalyzed carbonylation of alkyl bromides/tosylates to afford dialkyl ketones. The reaction shows broad substrate scope and good functional group tolerance.

Transesterification of diethyl oxalate (DEO) with phenol over MoO3-SiO2 catalysts prepared by the sol-gel technique (MoO3-SiO2 (SG)) and the impregnation method (MoO3-SiO2 (I)) was conducted to produce diphenyl oxalate (DPO), which can be used as a precursor for manufacturing diphenyl carbonate (DPC). The sample MoO3-SiO2 (SG) containing 12 wt % of MoO3 showed the best performance with 71.0% conversion of DEO and 32.0% selectivity to DPO. Compared to MoO3-SiO2 (I), improvements in the DEO conversion and DPO selectivity with MoO3-SiO2 (SG) were 16.1 and 7%, respectively. Crystal structure and phase composition of MoO3-SiO2 (I) and MoO3-SiO2 (SG) catalysts with varying MoO3 contents were investigated. The sample MoO3-SiO2 (SG) with a similar chemical composition to MoO3-SiO2 (I) has a larger specific surface area, indicating that the active component is well dispersed on the surface of the MoO3-SiO2 (SG) catalysts. Results of XRD and XPS measurements suggest a high degree of dispersion of MoO3-SiO2 (SG) catalysts that can account for an increase in DEO conversion and DPO selectivity. Coordinately unsaturated MoO3 species play a significant role in the catalytic performance of MoO3-SiO2 (SG) catalysts in transesterification of DEO with phenol. In addition, IR measurements of pyridine adsorption and NH3-TPD data indicate that the amount of acid sites on the surface of MoO3-SiO2 (SG) exceeds that found for the surface of MoO3-SiO2 (I). An enhanced concentration of surface MoO3 species in tetrahedral coordination coupled with the presence of weak Lewis acid sites appear to be the main reason why MoO3-SiO2 (SG) catalysts are superior to the MoO3-SiO2 (I) system.

MoO3/SiO2 catalysts for the transesterification of dimethyl oxalate (DMO) with phenol were prepared by both the thermal spreading (TS) and incipient wetness impregnation methods. The results showed that the 10%MoO3/SiO2 catalyst prepared by TS (10%MoO3/SiO2-TS) exhibited higher catalytic performance compared with the 10%MoO3/SiO2 catalyst prepared by incipient wetness impregnation (10%MoO3/SiO2-C). The catalysts were characterized by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, pyridine-IR spectroscopy, and NH3 temperature- programmed desorption. These analyses indicated that weak Lewis acid sites were formed on the catalyst surfaces and that the Mo species were present as monomeric MoO3 rather than as isolated molybdenum oxide or polymolybdate species on both catalysts, although the 10%MoO3/SiO2-TS exhibited better dispersion of MoO3 and a higher surface Mo content than the 10%MoO3/SiO2-C. Under the optimal transesterification reaction conditions (1.2 g 10%MoO3/SiO2-TS, T = 180 °C, n(DMO)/n(phenol) = 2, t = 4 h), the conversion of phenol was 70.9%, and the yields of methyl phenyl oxalate and diphenyl oxalate were 63.1% and 7.7%, respectively.

Titanium-containing mesoporous materials (Ti-MCM-41) were obtained by hydrothermal synthesis. Such materials are active catalysts for the transesterification of dimethyl oxalate and phenol to produce diphenyl oxalate. To understand the role of the Ti in the catalytic process, Ti-MCM-41 samples with different Si/Ti ratios (from 5 to 100) were prepared and the samples were analyzed by Fourier transform infrared spectroscopy, UV-visible spectroscopy, and ammonia temperature programmed desorption. It was concluded that the Ti is incorporated into the framework of the MCM-41 and formed weak Lewis acid sites. In addition, the number of Ti(IV) sites increased as the amount of titanium increased. X-ray powder diffraction, N2 adsorption-desorption and transmission electron microscopy results showed that the Ti-MCM-41 samples have a hexagonal arrangement of mono-dimensional pores. A large number of Ti(IV) sites coupled with the mesoporous structure and large pore diameters are favorable for the transesterification catalytic properties of Ti-MCM-41.

A series of nitrogen-doped nanoporous carbon (NNC) materials were prepared by directly carbonizing sol–gel composites containing aluminum phosphate, citric acid and hexamethylene tetramine (HMT). The structure and surface properties of these NNC materials were characterized by means of elemental analysis, N2 adsorption, X-ray powder diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), and X-ray photoelectron spectra (XPS). Besides possessing various oxygen-containing groups, these NNC materials also contain different types of nitrogen-containing groups, including pyridinic-N, pyrrolic-N and quaternary-N groups. The resulting NNC materials are highly active and selective heterogeneous catalysts for the transesterification of dimethyl oxalate (DMO) with phenol to produce methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO), and can be easily recycled by simple filtration. The presence of suitable surface basic sites should be mainly responsible for the excellent catalytic performance of NNC materials in the transesterification reaction.

Titanium-containing mesoporous (Ti-MCM-41) materials were prepared by microwave irradiation method at different temperature (from 353 K to 413 K) in 40 min, a much shorter period of crystallization time than that by hydrothermal method. Various characterization techniques, including XRD, FT-IR, N 2 adsorption and desorption, ICP, DRUV–vis, pyridine-FTIR, NH 3 -TPD and particle size analysis were carried out to investigate the physicochemical properties of these samples. Results showed that the samples prepared by microwave irradiation method have typical long-range order of hexagonal MCM-41 structure. Titanium incorporates into the silica framework and Ti species are mostly in tetrahedral coordination. Ti-MCM-41 molecular sieves were active as catalysts for transesterification of dimethyl oxalate and phenol to produce diphenyl oxalate and the optimal heating temperature is 393 K. The small particle size, large surface area and plenty of Ti(IV) active centers inside the framework, which provide more weak acid sites, are favorable for improving the catalytic properties.

Physicochemical properties of silica-supported titanium oxide catalysts as well as their performances for transesterification of dimethyl oxalate (DMO) with phenol to methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO) have been investigated systematically. Various wt % of TiO2 were loaded on SiO2 by a two-step wet impregnation method. The surface properties of TiO2/SiO2 catalysts were explored by various characterization techniques (BET, SEM, ICP, XPS, XRD, FTIR of pyridine adsorption, and NH3-TPD). Catalytic performances of TiO2/SiO2 catalysts were found to be strongly dependent on TiO2 dispersion and surface acidity. Monolayer dispersion capacity of TiO2 on silica was estimated to be about 4.0 TiO2 molecules per nm2 (SiO2) and no crystalline TiO2 was detected at TiO2 loading less than 12 wt %. FTIR and TPD analysis suggested that weak Lewis acid sites on the surface of TiO2/SiO2 were responsible for their unique selectivity to the target products, MPO and DPO. An optimization of reaction conditions for the transesterification of DMO with phenol was performed over 12 wt % TiO2/SiO2 calcined at 550°C. In addition, we studied the disproportionation reaction from MPO to DPO via a catalytic distillation process, which is highly efficient to promote formation of the desired DPO. © 2008 American Institute of Chemical Engineers AIChE J, 2008

Two kinds of hybrid inorganic–organic catalysts (denoted as Cp′-MCM-41 and Cp″-MCM-41) are prepared by grafting methylcyclopentadienyl (Cp′) or pentamethylcyclopentadienyl (Cp″) group onto the surface of mesoporous MCM-41. Such cyclopentadienyl-functionalized materials are active for the transesterification of dimethyl oxalate (DMO) with phenol. Under test conditions, Cp″-MCM-41 gives higher conversion of DMO and selectivity of diphenyl oxalate (DPO) than Cp′-MCM-41, and this might be assigned to the relatively strong Lewis basicity of Cp″ group.

The authors present results of an investigation into the dispersion of MoO3 on TiO2-SiO2 composite and its reactivity in transesterification of dimethyl oxalate (DMO) with phenol to produce methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO). They examined the effects of support composition, MoO3 content, and reaction time on activities of the transesterification. The results show that MoO3/TiO2-SiO2 is more active and selective than MoO3/TiO2, MoO3/SiO2, and TiO2/SiO2 catalysts in the transesterification reaction. The best catalytic performance is obtained over a 12%MoO3/8%TiO2-SiO2, providing a 71.8% DMO conversion and 59.0%, 40.1% selectivities for MPO and DPO, respectively. Through employing X-ray diffraction and inductively coupled plasma-optic emission spectrometry, they show evidence strongly suggesting that improvement of catalytic reactivity over the TiO2-modified SiO2 support can be ascribed to the enhanced metal oxide support interactions and the increased dispersion capacity of MoO3 phase. They also present evidence showing that incorporation of TiO2 in SiO2 can elevate the monolayer dispersion capacity of MoO3 on SiO2. Thus, they conclude that increased DPO selectivity from MoO3/TiO2-SiO2 catalysts can be primarily attributed to the improvement of MoO3 dispersion and the synergistic effect between amorphous MoO3 and amorphous TiO2. © 2008 American Institute of Chemical Engineers AIChE J, 2008

The transesterification of dimethyl oxalate (DMO) with phenol is studied on various Ti-containing phosphate (Ti-P-O) catalysts. The weak acid-base characteristics of Ti-P-O catalysts are responsible for the high activity and selectivity to methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO).

Diphenyl carbonate (DPC) is considered as a substitution for phosgene to synthesize polycarbonate resins. Conventional production of DPC involves reactions of phosgene and phenol. However, the phosgene process has drawbacks such as environmental and safety problems associated with using highly toxic phosgene as the reagent, which results in the formation of chlorine salts, and copious amounts of methylene chloride as the solvent. For these reasons, environmentally friendly processes for DPC production without using phosgene have been proposed and developed in the past decades. So far, the most promising alternatives appear to be the transesterification of dimethyl carbonate (DMC) and phenol, the direct oxidative carbonylation of phenol, and transesterification of dialkyl oxalates and phenol. This paper attempts to review recent literature concerning process design and catalytic chemistry for these phosgene-free approaches. The advantages and disadvantages are discussed for each reaction. Strategies to overcome potential problems are provided. The perspectives to improve catalytic efficiency of phosgene-free process are proposed.

The transesterification of dimethyl oxalate (DMO) with phenol over stannum modified TS-1 was conducted to prepare methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO), which could be used to produce diphenyl carbonate (DPC). The component, structure and phase of TS-1 catalysts with various Sn loadings were investigated. The relationship between the catalytic properties and the Sn loadings was discussed. The results indicated that, although the Sn-modified TS-1 catalysts had fewer Lewis acid sites than the unmodified TS-1, its catalytic activity was increased greatly by the interaction of Sn with Ti–O–SiO3 weak Lewis acid centers. The catalyst of TS-1 with 2 wt% Sn loadings performed best, giving 50.3% conversion of dimethyl oxalate and 99.2% selectivity to the target products. By means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX), the relationship between the catalytic properties and the structure of Sn dispersed on the surface of TS-1 was studied in detail. At Sn loadings below 2 wt%, Sn was highly dispersed, but at higher loadings it was crystallized into bulk tin dioxide, where the interaction between Ti and Sn was not evidently observed, leading to decreased catalytic activity. XPS results showed that Ti could not be detected even at 1 wt% Sn loadings. EDX results indicated that the content of Ti on the surface decreased with increasing Sn loadings, but the decrease in Ti content was much less than the increase in Sn content. Moreover, NH3-TPD and FTIR analyses of adsorbed pyridine showed that there were only weak Lewis acid centers on all catalysts and the Sn loadings hardly affected the acid strength of the catalysts.

Transesterification of diethyl oxalate (DEO) with phenol to form diphenyl oxalate (DPO) has been carried out in liquid phase using MoO3/SiO2 solid acid catalyst with high conversion and 100% selectivity. A series of MoO3/SiO2 catalysts with different Mo loadings (1–20 wt%) were prepared using sol–gel technique and characterized using X-ray diffraction analysis (XRD), BET specific surface area, temperature-programmed desorption (TPD) of ammonia, and FTIR spectroscopic analysis of adsorbed pyridine. XRD analysis revealed the amorphous nature of the catalyst up to 10 wt% MoO3 loading and the formation of crystalline α-MoO3 phase on amorphous silica support with higher MoO3 loading. BET surface area showed high surface area for catalysts prepared by sol–gel technique with lower MoO3 content; the surface area decreases with increasing MoO3 loading. Ammonia TPD shows much higher acid strength compared to the catalysts prepared by impregnation technique. Among the series of catalysts prepared, MoO3/SiO2 containing 1 wt% MoO3 was found to be the most active catalyst for transesterification reaction, with a maximum DEO conversion of 80.9 and 100% selectivity for DPO. The effects of reaction temperature and catalyst concentration on conversion and product selectivity have been investigated.

A new preparation method for supported MoO3 catalyst, slurry impregnation, has been described and compared with the conventional impregnation method. Slurry MoO3/water is used instead of the solution ammonium heptamolybdate, AHM [(NH4)6Mo7O24]. The MoO3/γ-alumina, MoO3/active carbon, and MoO3/silica catalysts with different Mo loadings were prepared by slurry and by conventional method. The low solubility of MoO3 was sufficient to transport molybdenum species from solid MoO3 to the adsorbed phase. The equilibrium was achieved after several hours at 95 °C based on the loading amount of molybdenum. Only the process of drying was needed; calcination was not necessary and was left out. This is an important advantage for active carbon support because oxidative degradation of active carbon impregnated by molybdena starts at a relatively low temperature of about 250 °C during calcination on air. The activity was tested in the transesterification of dimethyl oxalate (DMO) and phenol at 180 °C. The dependences of catalytic activity on Mo loadings for the slurry prepared catalysts were similar to the dependences for the samples prepared by the conventional impregnation method with AHM. The activities of the slurry impregnation MoO3/γ-Al2O3 catalysts were almost the same as those of catalysts prepared conventionally. Although the performances of slurry impregnation MoO3/SiO2 catalysts for transesterification of DMO were slightly better than those of the corresponding catalysts prepared by conventional impregnation, no waste solution and no calcining nitrogenous gases were produced. Therefore, we conclude that the new slurry impregnation method for preparation of supported molybdenum catalysts is an environmentally friendly process and a simple, clean alternative to the conventional preparation using solutions of (NH4)6Mo7O24. The present work will lead to a remarkable improvement in the catalyst preparation for the transesterification reaction.

Rhodium(I) complexes, [Rh(COD)(amine) 2 ](PF 6 ) (COD = 1,5-cyclooctadiene, amine = 4-picoline, 3-picoline, 2-picoline, pyridine, 3,5-lutidine or 2,6-lutidine) immobilized on poly(4-vinylpyridine) in contact with water catalyzed both the hydroxycarbonylation of 1-hexene to propionic acid and the water-gas shift reaction (WGSR). The role of the coordinated amine on the catalytic activity was examined.

The transesterification of dimethyl oxalate (DMO) with phenol over stannum modified Hβ was conducted to prepare diphenyl oxalate (DPO) used to produce diphenyl carbonate (DPC). The component, structure and phase of Hβ catalysts with various Sn loadings were investigated. The relationship between the catalytic properties and the amount of Sn loadings was discussed. The catalyst of Hβ with 2 wt.% Sn loading based on metal performed best, giving 75.3% conversion of DMO and 24.0% selectivity to DPO. At Sn loadings below 2 wt.%, Sn was highly dispersed as monolayer, but at higher loadings it was crystallized into bulk tin dioxide, and the catalytic activity decreased. The curve of XPS peak intensity ratio of Sn 3d/Si 2p versus Sn loadings estimated the dispersed capacity of Sn on Hβ to be 2.1% Sn loading, which was in good agreement with the value obtained from XRD analysis. NH3-TPD results showed that the amount of Sn loading had effect only on the strength of the weak surface acid sites on Hβ. And the decrease of selectivity to anisole was not due to the change of the weak acid sites. Maybe, SnO2 accelerated to the formation of MPO and DPO. FTIR analysis of adsorbed pyridine showed that many Lewis acid sites and few Bronsted acid sites were present on Hβ catalysts with or without Sn modified. The acid sites together with SnO2 active centers catalyzed the transesterification of DMO with phenol. Especially, SnO2 active centers were in favor of the disproportionation of MPO into DPO.

A series of bimetallic MoO3-SnO2/SiO2 catalysts with various Mo and Sn contents ranging from 1–16 wt.% were prepared by sequential impregnation with molybdate species and cationic Sn complexes using the wet impregnation method. The performance of these catalysts in the transesterification of dimethyl oxalate (DMO) with phenol was compared with corresponding stannum- and molybdenum-supported catalysts prepared by the same method. The results indicated that the catalyst of MoO3-SnO2/SiO2 with 14 wt.% Mo and Sn contents performed best, giving 74.6% conversion of DMO and 99.5% selectivity to target products, methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO). The component, structure and phase of MoO3-SnO2/SiO2 catalysts with various Mo and Sn contents were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), BET specific surface area measurement, temperature-programmed desorption of ammonia (NH3-TPD), and FT-IR analysis of adsorbed pyridine. It was observed that interdispersion between MoO3 and SnO2 plays an important role in modifying the catalytic behavior. NH3-TPD and FT-IR analysis of adsorbed pyridine results showed that only weak Lewis acids were present on the catalyst surface and the amounts of Mo and Sn loadings has hardly effected the strength of the surface acid. The weak Lewis acid sites catalyzed transesterification of DMO with phenol and Sn gave a promotional effect.

The transesterification of dimethyl oxalate (DMO) with phenol to produce methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO) was carried out over a SnO2/SiO2 catalyst. The evaluation results showed that SnO2/SiO2 had better activity and total selectivity to MPO and DPO than many conventional ester exchange catalysts. Especially, SnO2/SiO2 was in favor of the disproportionation of MPO into DPO compared with TS-1, MoO3/SiO2, and MoO3−SnO2/SiO2 catalysts. The conversion of DMO was 46.7% and the selectivity to DPO was 22.5% at 8% Sn loadings, which was the maximum at different Sn loadings. IR of adsorbed pyridine and NH3-TPD characterization indicated that the desirable catalytic activity of SnO2/SiO2 could be ascribed to its weak Lewis acidity. The structure and chemical state of tin species in SnO2/SiO2 had been investigated by X-ray diffraction. SnO2 active centers dispersed on a SiO2 carrier with a high specific surface area were of benefit to the transesterification.

The transesterification of dimethyl oxalate (DMO) with phenol to produce methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO) was carried out over TiO 2 /SiO 2 catalyst. The evaluation results showed that TiO 2 /SiO 2 had better activity and excellent selectivity to target products compared with many conventional ester exchange catalysts. The total selectivity to MPO and DPO kept about 99.0% over TiO 2 /SiO 2 and the conversion of DMO was 66.7% at 10% Ti loading, which was the maximum at different Ti loading. The structure and the chemical state of titanium species in TiO 2 /SiO 2 had been investigated by XRD and XPS. The surface Ti(IV) species in the form of a monolayer was dominant until 6% Ti loading, while crystalline TiO 2 was detected at 8% Ti loading. IR of adsorbed pyridine and NH 3 -TPD characterization indicated that the desirable catalytic activity of TiO 2 /SiO 2 could be ascribed to its weak Lewis acid. Lewis acid sites cooperated with TiO 2 to catalyze the synthesis of MPO and DPO.

The transesterification of dimethyl oxalate (DMO) with phenol to methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO) was carried out in liquid phase under facile catalytic conditions. A series of bimetallic, MoO3–SnO2/SiO2, catalysts with various Mo and Sn content were prepared by sequential impregnation of cationic Mo species and cationic Sn complexes using impregnation method. The effects of mass ratio of Mo:Sn, amount of Sn additive, and Mo(Sn) laoding amount on activities of transesterification of dimethyl oxalate with phenol were investigated. The evaluation results showed that MoO3–SnO2/SiO2 catalyst with 14 wt% Mo(Sn) content performed best, giving 74.6% DMO conversion and 99.5% selectivity to MPO and DPO. This new heterogeneous catalyst provided not only an excellent selectivity (99% to MPO and DPO) and high yield of MPO and DPO but also a simple and practical protocol for DPC synthesis.

A series of MoO3/SiO2 catalysts were prepared with Mo loadings ranging from 1 to 16 wt% and applied to the transesterification of dimethyl oxalate (DMO) with phenol. The results showed that the catalyst of MoO3/SiO2 with 1 wt% Mo content performed best, giving 54.6% conversion of DMO and 99.6% selectivity to target products, methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO). The surface properties were investigated by means of X-ray diffraction (XRD), X-ray photoelectron (XPS), BET specific surface area, temperature-programmed desorption (TPD) of ammonia, and FTIR analysis of adsorbed pyridine. XPS and XRD analyses indicated that Mo(VI) species was highly dispersed at low Mo loading and MoO3 of the crystal structure appeared at higher loading. NH3-TPD characterization and FTIR analysis of adsorbed pyridine demonstrated that only Lewis weak acids were present on catalyst surface and the amount of Mo loading has little effect on the strength of the surface acid on MoO3/SiO2. The catalytic results exhibited that the synergetic effect of Mo active centers with weak Lewis acid sites catalyzed transesterification of DMO with phenol.

The transesterification of dimethyl oxalate (DMO) with phenol to methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO) was carried out in liquid phase using a variety of solid catalysts. The evaluation results showed that MoO3/SiO2 had a better activity and excellent selectivity to target products compared with many conventional ester exchange catalysts. The effects of supports, loading amount of Mo, catalyst amount and reaction time were investigated. Under catalytic reaction conditions, the total selectivities to methyl phenyl oxalate and diphenyl oxalate were up to 98%. And 49.3% yield of methyl phenyl oxalate and 17.3% yield of diphenyl oxalate were obtained at 453 K in the presence of MoO3/SiO2. A plausible mechanism for the transesterification of dimethyl oxalate with phenol to methyl phenyl oxalate over MoO3/SiO2 was proposed.

The influence of molybdenum content on the catalytic performance in the transesterification of dimethyl oxalate (DMO) with phenol to methyl phenyl oxalate (MPO) and diphenyl oxalate (DPO) was investigated. The results indicated that the MoO3/Al2O3 catalyst with 14 wt% Mo content gave maximal DPO yield with 6.1% and 75.1% DMO conversion. The component, structure and phase of MoO3/Al2O3 catalysts were characterized by means of X-ray diffraction (XRD), BET specific surface area, temperature-programmed desorption of ammonia (NH3-TPD), and FTIR analysis of adsorbed pyridine.

The transesterification of dimethyl oxalate with phenol to produce methyphenyl oxalate and diphenyl oxalate was carried out in liquid phase using a heterogeneous catalyst. The evaluation results showed that TS-1 had better activity and excellent selectivity to target products compared with many conventional ester exchange catalysts tested. Two hours as the duration of the reaction was appropriate. Under the catalytic reaction conditions, framework IR and the reaction results jointly proved that the best calcination temperature was 823 K at which the amount of acid sites measured by IR of adsorbed pyridine reached a maximum. X-ray diffraction of TS-1 did not show much variation with changing calcination temperatures from 723 to 923 K. The characterization of the catalyst, by means of IR of adsorbed pyridine and NH 3 -TPD indicated that the desired catalytic activity of TS-1 could be ascribed to its weak Lewis acidity. Tin modified TS-1 showed a better performance in activity and selectivity. The conversion of dimethyl oxalate was improved up to 50.3% when Sn loading was 2, while the selectivity was above 99% over all Tin modified TS-1 molecular sieves.

The transesterification of dimethylcarbonate and phenol has been studied in a continuous gas flow reactor at high temperatures which were found to be favorable thermodynamically for high yields of methylphenylcarbonate (MPC). Among various solid catalysts, TiO 2 /SiO 2 showed the highest activity and selectivity for MPC. The structure and the chemical state of titanium species in TiO 2 /SiO 2 have been investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and X-ray absorption near edge structure (XANES) of Ti K -edge. It was observed that the titanium species was highly dispersed on silica. Below 10 wt% Ti loading, the titanium phase was not observed by XRD, yet weak XRD peaks of anatase were detected at higher loadings. The Ti K -edge XANES spectra and XPS analyses indicated that Ti(IV) species in the form of a monolayer was dominant below 5 wt% Ti loadings and TiO 2 of the anatase structure appeared at higher loadings. The amount of the surface Ti(IV) species measured by XPS increased with Ti loadings and was saturated above 10 wt% in the same manner as the selectivity to MPC changed with Ti loadings. This suggested that surface Ti(IV) species was directly responsible for the selective synthesis of MPC. The crystalline anatase TiO 2 was also an active and selective catalyst for the transesterification, yet it contributed to decrease in activity by coking.

The transesterification of dimethyl carbonate with phenol to produce methyl phenyl carbonate was carried out in an autoclave using a variety of solid catalysts. MoO 3 SiO 2 was found to have a very high activity for this transesterification. Thus, a 17.1% yield of methyl phenyl carbonate based on phenol was obtained at 433 K in the presence of MoO 3 SiO 2 . MoO 3 SiO 2 was also an active catalyst for the disproportionation of methyl phenyl carbonate into diphenyl carbonate and dimethyl carbonate. A 48% yield of diphenyl carbonate was attained over MoO 3 SiO 2 at 443 K. These yield values are probably very close to those at the thermodynamic equilibrium.

Dimethyl carbonate (DMC) is a unique molecule having a versatile reactivity. The transesterification of DMC with phenol gives methyl phenyl carbonate, which is converted into diphenyl carbonate (DPC) by disproportionation. MoO 3 /SiO 2 is an active catalyst for both reactions. DPC is an essential monomer in the non-phosgene route for polycarbonates. The methoxycarbonylation of aniline gives methyl N -phenyl carbamate in the presence of a lead compound. This reaction offers a non-phosgene route to isocyanates. As a methylating agent, DMC can be a substitute for methyl halides and dimethyl sulfate, toxic and corrosive chemicals. Phenylacenitrile, aniline and phenol are selectively methylated with DMC over zeolites in the vapor-phase. The reaction of DMC with silica offers a simple and clean method for synthesizing Si(OCH 3 ) 4 .