Carbon-encapsulated nanonickel particles were prepared by heating nickel acetate highly dispersed in cured phenolic resin at 673 K in N2. The metallic nickel cores were about 50—80 nm in diameter, completely encapsulated with carbon shells about 10 nm thick. No byproduct, such as carbides, carbon rods, and carbon fibers, were formed in the samples prepared this way. The carbon shells prevented the metallic nickel cores from oxidation by air at high temperatures. The metallic cores remained even after the encapsulated particles were treated with 6 M hydrochloric acid solution for 24 h. The surface of the encapsulated particles was originally hydrophobic due to the hydrophobic property of the carbon shells formed under the high carbonization temperature. The treatment of the encapsulated particles with O3 at room temperature generated substantial amounts of carboxylic groups on the outer surface of carbon shells, leading to the hydrophilic surface of the encapsulated nanonickel particles.

•Decomposition of PODEn without water produced PODEn±i that followed Schulz-Flory law.•Decomposition of PODEn in water produced only FA, MeOH and PODE1.•Release of FA was constant from PODEn in water due to the 0th order decomposition.•PODEn was found to be better than FA for the synthesis of bisphenol F.•PODE2 was found to be better than other PODEn for the synthesis of bisphenol F.The decomposition of polyoxymethylene dimethyl ethers (PODEn) with and without the presence of water was investigated. Without water, the products from the decomposition of PODEn (n = 2–5) contained smaller (PODEn-i) and larger (PODEn + i) homologues that followed the Schulz-Flory rule. However, the products from the decomposition of PODEn (n = 1–5) in water contained only formaldehyde (FA), methanol and dimethoxymethane without any other PODEn ± i. The reaction kinetics showed that the decomposition of PODEn in water was pseudo-zeroth order with respect to PODEn. The rate constants with pre-exponential factors and apparent activation energies were obtained for the decomposition reactions in water. Based on the above results, PODEn (n = 1–5) were used as reactants to react with phenol for the synthesis of bisphenol F (BPF) catalyzed by phosphoric acid. PODE2 was found to be better than FA for the synthesis of BPF with the improved yield and selectivity.Download high-res image (230KB)Download full-size image

•The Ni/LaAlSiO was highly active and selective for the amination of isopropanol.•Dehydrogenation of isopropanol was the rate-limiting step for the amination.•Surface basicity promoted the dehydrogenation of isopropanol on Ni.•Desorption of isopropylamine was another key step for the amination.•Surface basicity promoted the desorption of isopropylamine from Ni.Ni/AlSiO, Ni/LaO and Ni/LaAlSiO catalysts were studied for the amination of isopropanol (IPO) to isopropylamine (IPA). It was confirmed that the dehydrogenation of IPO to adsorbed acetone was the rate-limiting step for the amination of IPO. The Ni/LaAlSiO exhibited high activity for the dehydrogenation of IPO to acetone due to its high density of active Ni sites and strong surface basicity, and thus the high activity for the amination of IPO. In addition, the strong surface basicity of Ni/LaAlSiO promoted the desorption of IPA and inhibited the condensation reaction of IPA with adsorbed acetone, leading to the increased selectivity to IPA. In particular, the microcalorimetric co-adsorption results showed that IPA might be the most abundant surface species in the reaction, and the surface basicity promoted the desorption of IPA and thus the adsorption of reactants, leading to increased activity for the amination of IPO.Download high-res image (121KB)Download full-size image

•Large Fe particles (38 nm) could not be completely phosphided by PPh3 even at 593 K.•Smaller Fe particles (29 nm) could be fully phosphided into Fe2P by PPh3 at 543 K.•Fe particles of 29 nm could also be fully phosphided into FeP by PPh3 at 593 K.•Fe2P was not stable and converted to other phases during the hydrotreating reactions.•FeP was found to be stable and active for the hydrotreating reactions.Highly loaded iron phosphides were prepared by the phosphidation of unsupported Fe, 80%Fe/C and 60%Fe/C with Fe metal particle sizes of 38, 35 and 29 nm, respectively, using triphenylphosphine in liquid phase. The large Fe particles such as those in the unsupported sample could not be phosphided completely, while the smaller ones in the 60%Fe/C could be completely phosphided into Fe2P at 543 K for 18 h and FeP at 593 K for 33 h, respectively. The FeP/C was found to be significantly more stable and thus generally more active than the Fe2P/C for the hydrotreating reactions.The Fe2P/C and FeP/C catalysts were prepared through the phosphidation of a reduced 60%Fe/C by PPh3 in liquid phase at 543 and 593 K, respectively. The FeP was found to be stable and active, while the Fe2P was much less stable and hence generally less active than FeP, for the hydrotreating reactions.Download high-res image (238KB)Download full-size image

The NiAlOx and NiSiOx complex oxides with high surface areas were prepared by the co-precipitation method through the control of acidity of solutions. Nickel species were found to be highly dispersed in these complex oxides and a remarkable feature was that the incorporation of large amount of nickel cations into SiO2 generated the great amount of surface acid sites. Upon the sulfidation by CS2, the sulfided catalysts were found to be highly active for the conversion of 1-hexene to different products formed from the three main competitive reactions (skeletal isomerization, double bond isomerization and hydrogenation of all hexenes). The high yield of skeletal isomerization of 1-hexene on a sulfided NiSiOx (55 %) could be attributed to the high density of acid sites for the adsorption of 1-hexene as well as the low hydrogenation activity of nickel species on this catalyst. In contrast, the high yields of direct hydrogenation and double bond isomerization of 1-hexene on the sulfided NiAlOx might be due to the high hydrogenation activity of nickel species as well as the surface acidity and basicity on the catalyst.The sulfided NiAlOx and NiSiOx complex oxides were highly active for the conversion of 1-hexene to different products. The high yield of skeletal isomerization of 1-hexene on the sulfided NS10 (55 %) could be attributed to the high density of acid sites for the adsorption of 1-hexene.

•Sequence of electron transition in three bisphenol F isomers from difficulty to ease is 2,2′-BPF, 2,4′-BPF, and 4,4′-BPF.•The FTIR absorption peak strength of the 4,4′-BPF increases significantly in a polar solvent.•The Raman spectra variation of the 4,4′-BPF in the polar solvent is limited.•New characteristic peaks occur in the FTIR spectra and Raman spectra along with an increase in the hydroxyl group amount.•The order of the red shifts in the UV spectra is opposite of the order of the substitution element electronegativity values.The quantum chemical calculation method is used in this paper to study the energy difference between the highest occupied molecular orbitals and lowest unoccupied molecular orbitals of three bisphenol F (BPF) isomers. The results show that the minimum energy difference occurs at 4,4'-dihydroxydiphenylmethane (4,4′-BPF); the middle energy difference occurs at 2,4'-dihydroxydiphenylmethane (2,4′-BPF); and the maximum energy difference occurs at 2,2'-dihydroxydiphenyl- methane (2,2′-BPF). Based on these results, the electron transition in 4,4′-BPF is easier than that in 2,4′-BPF, while the electron transition in 2,2′-BPF is the most difficult. This paper investigates the effect of the hydroxyl group, specifically concerning the spectroscopic properties of BPF isomers by observing the solvent effect, hydroxyl group amount and the element substitution of an oxygen atom in the hydroxyl group. The solvent effect results show that infrared spectroscopy intensity increases significantly for 4,4′-BPF in the polar solvent (methanol and water), but does not increase proportionally to the electric constant increase of the polar solvent. The multi hydroxyl substitution of BPF isomers results show that with an increase in the hydroxyl group amount, new characteristic peaks occur in FTIR spectra and Raman spectra, while the characteristic peaks in UV spectra are smoother in the range of 240–300 nm. The element substitution results show that the red shifts occur in a different element substituted 4,4′-BPF isomer in UV spectra, and the red shifts order is opposite of that involving substitution element electronegativity.

Catalysts 60% Ni/Al2O3 and 60% Ni/4% ZrO2–Al2O3 were prepared, and it was found that the addition of ZrO2 promoted reduction while maintaining the high dispersion of supported nickel. Upon phosphidation by triphenylphosphine (PPh3) in the liquid phase, the two catalysts were converted into corresponding Ni2P/Al2O3 and Ni2P/ZrO2–Al2O3 catalysts with highly dispersed Ni2P particles (6.3 and 6.8 nm, respectively), high CO uptakes (305 and 328 μmol g−1, respectively) and thus high activities for the hydrodesulfurization (HDS) of dibenzothiophene (DBT) and hydrogenation of tetralin to decalin. In particular, the Ni2P/ZrO2–Al2O3 was found to be significantly more active than the Ni2P/Al2O3 for the HDS of DBT and hydrogenation of tetralin to decalin. Although the presence of ZrO2 did not affect the heat of adsorption of CO on Ni2P, it significantly increased the heat and uptake of adsorption of H2 on Ni2P, which might account for the increased activity of Ni2P promoted by ZrO2.

Ni/Al2O3, Ni/MgAlO, and Ni/MgO catalysts were studied for the hydrogenation of pyridine to piperidine. Microcalorimetric adsorption and infrared spectroscopy were used to study the adsorption of CO, H2, pyridine, and piperidine on the catalysts. It was found that the basic support (MgO) increased the heat of adsorption of CO on Ni, due to the increased surface electron density of Ni, while weakened the strength of H–Ni, which might be a reason for the decreased activity of Ni/MgO for the hydrogenation of pyridine. In contrast, the acidic support (Al2O3) caused the electron-deficient surface metallic Ni that enhanced the adsorption of H2 and pyridine and thus favored the hydrogenation of pyridine. In addition, it was found that pyridine was more strongly adsorbed on Ni than piperidine although piperidine is a stronger base than pyridine, indicating that the electron-enriched aromatic ring of pyridine might be involved in the adsorption of pyridine on Ni, which was favored on the electron-deficient surface Ni and acidic support.

Ni2+ and H2PO2− with a molar ratio of 1/3 were heated at 423 K in a eutectic mixture composed of choline chloride and urea, resulting in the formation of a mesoporous and amorphous material with surface area of about 210 m2 g−1. Heat treatment of this material in H2 at 673 K led to the formation of crystalline Ni2P (25%) supported on amorphous and mesoporous Ni3(PO4)2-Ni2P2O7 (shortened as NiPO) with a surface area of about 130 m2 g−1. The NiPO was presumably produced from the reaction of unreduced Ni2+ with PO43− formed from the oxidation of H2PO2− in the eutectic mixture, which might also act as a template for the formation of mesopores in NiPO. The catalyst 25% Ni2P/NiPO exhibited a quite high uptake for the adsorption of CO (38 μmol g−1), and thus it is quite active for the hydrodesulfurization of dibenzothiophene, hydrodenitrogenation of quinoline and hydrogenation of tetralin in a model diesel.

Melamine formaldehyde resins were synthesized with encapsulated CaCl2 as a template. Carbonization at high temperatures led to the formation of carbon materials containing N atoms. Washing with de-ionized water removed encapsulated CaCl2, resulting in the formation of mesopores (3–30 nm) with the high surface areas (770–1300 m2/g). The template can be recycled and the method is simple and cost effective as compared to the hard template techniques. The mesoporous carbons containing nitrogen (NMC) thus prepared exhibited the amphipathic surfaces (both hydrophilic and lipophilic) and adsorbed great amount of water and benzene. In addition, the incorporated N atoms exhibited quite strong basicity for the adsorption of great amount of SO2.Graphical abstractMesoporous carbons containing nitrogen were prepared through the carbonization of melamine formaldehyde resins with CaCl2 as a template, which exhibited high surface area and strong surface basicity for the adsorption of SO2.Highlights► Mesoporous carbons containing N were prepared from melamine formaldehyde resins. ► CaCl2 was used as a template which could be easily removed by washing with water. ► The carbons possessed high surface areas, mesopores and high contents of nitrogen. ► The carbons exhibited amphipathic (both hydrophilic and lipophilic) surfaces. ► The carbons exhibited strong surface basicity and adsorbed great amount of SO2.

A microkinetic analysis of the preferential oxidation of CO in H2 over Ir−Fe/SiO2 catalyst is reported. Based on the results of in situ diffuse reflectance infrared spectroscopy, microcalorimetry, Mössbauer spectroscopy, and steady-state kinetic experiments in a microreactor, a microkinetic model is proposed that predicts the experimental results well. The model suggests that the reaction between adsorbed H and O for the formation of OH is rate-limiting for the PROX reaction, whereas the surface reaction between adsorbed CO and O is rate-determining for CO oxidation. In addition, the model predicts that the oxidation of adsorbed CO by surface OH is the dominant pathway for the PROX reaction. The surface coverages of different intermediates are also predicted by the model. According to this model, we can conclude that the presence of H2 increases the surface concentration of OH and, hence, lowers the activation energy and increases the rate of the PROX reaction.

Vanadium oxides with high surface areas are desirable for the applications in catalysis and lithium batteries. A new method has been developed in this work for the preparation of mesoporous VO2 with the surface area of about 180 m2/g and slit-shaped mesopores. In this simple method, V2O5 was first dissolved in aqueous solution of H2O2 and the solution was evaporated at 353 K to form a gel with layered structures. After being dried in n-butanol at 353 K, the layered gel intercalated with n-butanol was evacuated at 673 K to form the mesoporous VO2. Characterizations showed that the prepared mesoporous VO2 possessed much stronger surface acidity and redox ability than the traditional V2O5. Accordingly, it exhibited much higher activity than V2O5 for the conversion of isopropanol in air and the selective oxidation of toluene to benzaldehyde and benzoic acid. In addition, the mesoporous VO2 displayed high thermal stability. It possessed the surface area of 130 m2/g even after the reaction of selective oxidation of toluene at 633 K.

Mesoporous SBA-15 was prepared by using P123 as a template. The precursor with the template was calcined in an inert atmosphere so that carbon films might be formed in pores of SBA-15 due to the decomposition of template. The SBA-15C thus formed contained 3% C and exhibited similar pore structures as the SBA-15. Both SBA-15 and SBA-15C were used to support 20% nickel (by weight) via impregnation. It was found that doping with carbon films enhanced the dispersion of supported nickel. However, calcination at high temperatures before the reduction had a negative effect on the dispersion of nickel. The un-calcined 20%Ni/SBA-15C after the reduction in H2 at 673 K exhibited the highest dispersion of nickel (42%) and smallest average particle size of about 2.4 nm, in the catalysts studied in this work. It was also the most active catalyst for the hydrogenation of toluene to methyl cyclohexane. Conversion of toluene could be detected even at room temperature and atmospheric pressure for the catalyst in a fix-bed reactor, and 100% conversion of toluene was reached when temperature was raised to 358 K.

In this study, Ir−Fe/SiO2 catalyst was prepared by coimpregnation and investigated for preferential oxidation of CO under the presence of H2. It was found that the presence of H2, even in a slight excess, led to a large increase in the reaction rate for CO oxidation over the Ir−Fe/SiO2 catalyst, which was quite different from the case of Ir/SiO2. To reveal the promotional role of Fe associated with the presence of H2, quasi in situ Mössbauer spectroscopy, in combination with in situ DRIFTS and microcalorimetry, was employed. The results showed that the relative amount of Fe2+ increased with increasing H2 concentration in the reaction stream, well consistent with the trend of reaction rate for CO conversion, strongly suggesting that Fe2+ is the active site for oxygen activation. H2 promoted CO oxidation mainly via maintaining a substantial amount of Fe existing as Fe2+.

60%Ni/MgO (wt%) catalysts were prepared by the co-precipitation method and the influence of n-butanol treatment was investigated. The results showed that the treatment with n-butanol improved the dispersion and reducibility of supported nickel, resulted in an increase of H2 uptake from 410 to 582 μmol/g, corresponding to an increase of active Ni surface area from 32 to 46 m2/g (increased by 42%). Accordingly, the catalytic activity for the hydrogenation of toluene to methyl cyclohexane was significantly increased. Microcalorimetric adsorption of H2 and CO indicated that the treatment with n-butanol increased the amount of active metal sites on the surface, without the change of electron densities of supported nickel surface. Microcalorimetric adsorption of CO2 and NH3 revealed the strong surface basicity and weak surface acidity for the Ni/MgO catalysts, especially for the reduced ones. The initial heat for the adsorption of acetonitrile was measured to be about 130 kJ/mol on the Ni/MgO catalysts, indicating the strong interaction between acetonitrile and the supported nickel, which might be an important factor determining the activity of nickel for the hydrogenation of aliphatic nitriles. The surface basicity of the Ni/MgO catalysts might play a role in inhibiting the formation of secondary and tertiary amines and therefore improved the selectivity to primary amine during the hydrogenation of lauronitrile to laurylamine. In addition, the Ni/MgO-B catalyst prepared with n-butanol treatment seemed more active for the hydrogenation of lauronitrile.

A new and facile method was developed for the preparation of mesoporous carbon materials from soluble and hydrolyzable carbohydrates with a metal chloride template. The preparation procedure and related mechanism were demonstrated using fructose and ZnCl2 as examples of the carbon precursor and template, respectively. Since both fructose and ZnCl2 are soluble in water, they can be mixed homogeneously initially. Fructose was first hydrolyzed to hydroxymethylfurfural, which was then polymerized to form a resin; both reactions were catalyzed by the acidic ZnCl2. During the carbonization, ZnCl2 might act as an activation agent promoting the carbonization of cured resin and a template for the formation of mesopores. Mesoporous carbon materials with high surface areas (1400–2000 m2 g−1), large pore volumes (1.44–2.72 cm3 g−1) and 100% mesopores with an average size of 3–7 nm can be prepared by using this simple and cost-effective method. The materials could be used as adsorbents and catalyst supports for relatively large molecules.

Nanoparticles of Ni2P were simply prepared by a solid phase reaction of H2PO2− with Ni2+ in N2 at relatively low temperatures, which exhibited high activity for the hydrodesulfurization of dibenzothiophene and hydrodenitrogenation of quinoline.

Co-MCM-41 catalysts were synthesized and used to support the additional cobalt. Microcalorimetric adsorption of NH3 showed that the Co-MCM-41 and 5%Co/5%Co-MCM-41 exhibited stronger surface acidity than 5%Co/MCM-41. The surface acidity was greatly enhanced upon the sulfidation. The 5%Co/5%Co-MCM-41 after sulfidation possessed strong surface acidity with an initial heat of about 180 kJ/mol and coverage of about 1060 μmol/g for the adsorption of ammonia. The catalytic tests showed that little skeletal isomerization occurred on the Co−Mo/γ-Al2O3, whereas it occurred substantially over the MCM-41 related catalysts. Over 60% skeletal isomerizations were observed for the 5%Co/5%Co-MCM-41 at 573 K. In addition, a combination of the Co/Co-MCM-41 with a traditional Co−Mo/γ-Al2O3 catalyst showed not only the high hydrodesulfurization activity but also converted significant amounts of 1-hexene into branched hexanes. Thus, this technique might be used to compensate the loss of octane number of gasoline during its hydrodesulfurization by first converting linear olefins to branched ones followed by hydrogenating to branched alkanes.

Previous work showed that the V–Ag–O complex oxides exhibited quite good catalytic behavior for the selective oxidation of toluene to benzaldehyde. In this work, TiO2 was added into V–Ag–O by co-precipitation with a sol–gel method. Structural characterizations using X-ray diffraction and Fourier transform infrared spectroscopy indicated the phases of Ag2V4O11, Ag1.2V3O8 and TiO2 in the V–Ag–O/TiO2 before the reaction. No complex oxide phases involving titanium were observed. Thus, the addition of TiO2 seemed to generate the interfaces between TiO2 and the silver vanadates. The Ag2V4O11 and part of Ag1.2V3O8 were converted into Ag0.68V2O5 and metallic Ag during the reaction. The results of temperature programmed reduction, microcalorimetric adsorption of NH3 and isopropanol probe reaction in air revealed that the addition of TiO2 might increase both the surface acidity and redox ability of the catalysts. The increased redox ability seemed to improve the activity for the oxidation of toluene, but the increased surface acidity might lead to the decrease of selectivity to benzaldehyde. The V–Ag–O/TiO2 with 20% TiO2 exhibited significantly improved catalytic behavior for the selective oxidation of toluene to benzaldehyde, as compared to the un-promoted V–Ag–O catalyst. The conversion of toluene reached 7.3% over the V–Ag–O/20%TiO2 at 613 K with 95% selectivity to benzaldehyde.

The Co−Mo/γ-Al 2O 3 catalysts promoted with P and Mg were prepared and found to be highly active and stable for the hydrodesulfurization of commercial naphtha. The catalytic behavior of hydrogenation and isomerization of such catalysts were studied using model naphtha. The catalysts were found to be highly active for the hydrodesulfurization (HDS) of thiophene in hexane, but the activity was significantly inhibited by the presence of olefin. The model compound 1-hexene was found to be isomerized (mainly a double-bond shift with a little skeletal isomerization) and hydrogenated directly to n-hexane at the comparable rates over the sulfided Co−Mo/γ-Al 2O 3 catalysts. Microcalorimetric adsorption of ammonia showed the fairly strong surface acidity for the Co−Mo/γ-Al 2O 3 catalysts, which might be responsible for the isomerization activities. In addition, the hydrogenation and isomerization of 1-hexene seemed to proceed in a competitive way and were affected strongly by the solvents. The activity of hydrogenation was higher, while that of isomerization was lower for 1-hexene in heptane than in benzene. This result could be explained if it was supposed that the hydrogen transfer was the main pathway for the hydrogenation of olefins, considering that heptane is a better hydrogen donor than benzene. A pathway was also demonstrated in this work that 1-hexene could be first isomerized and then hydrogenated to isoalkanes of higher octane numbers. The other double-bond isomers generated from 1-hexene over the acidic sites were more difficult to be hydrogenated to n-alkanes, which might also reduce the octane number loss of naphtha during the hydrodesulfurization.

Chlorine free mesoporous TiO2 nanotubes (TNT) with high surface areas were prepared and used to support V2O5. The addition of V2O5 increased the surface acidity of TNT, which was further enhanced by the addition of Ti(SO4)2. The materials were characterized by X-ray diffraction (XRD), laser Raman spectroscopy (LRS), transmission electron microscopy (TEM), N2 and O2 adsorption, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (H2-TPR), and microcalorimetry and infrared spectroscopy (FTIR) for the adsorption of NH3. The catalytic behavior for the selective oxidation of methanol to dimethoxymethane (DMM) was evaluated. It was found that V2O5 was highly dispersed on TNT with the V2O5 loading lower than 20 wt%. The 6%SO42−/20%V2O5/TNT displayed the strong surface acidic and redox characters and exhibited excellent performance for the selective oxidation of methanol to DMM. The methanol conversion reached 64% with 90% selectivity to DMM over the SO42−/20%V2O5/TNT at 403 K.

Dimethoxymethane was synthesized from the direct oxidation of methanol with high conversion and selectivity over specially designed bifunctional V2O5/TiO2 catalysts with redox and enhanced acidic character, in which the surface acidity played an essential role for inhibiting the formation of formaldehyde through the enhanced condensation reaction of formaldehyde with methanol to produce dimethoxymethane.

CeO2 supported V2O5 catalysts were prepared by the wetness impregnation technique and their surface structures were characterized by O2 chemisorption, X-ray diffraction (XRD) and Raman spectroscopy (LRS). The surface acidity and basicity were measured by using microcalorimetry and infrared spectroscopy (FTIR) for the adsorption of NH3 and CO2. Temperature programmed reduction (TPR) was employed for the redox properties. In particular, isopropanol probe reactions with and without the presence of O2 were employed to provide the additional information about the surface acidity and redox properties of the catalysts. Variation of loading of V2O5 and calcination temperature brought about the changes of surface structures of dispersed vanadium species, and hence the surface acidic and redox properties. Structural characterizations indicated that V2O5 can be well dispersed on the surface of CeO2. The monolayer dispersion capacity was found to be about 8 V/nm2, corresponding to about 10% V2O5 by weight in a V2O5/CeO2 sample with the surface area of 80 m2/g. Vanadium species in the catalysts (673 K calcined) with loading lower than 10% were highly dispersed and exhibited strong surface acidity and redox ability, while higher loading resulted in the formation of significant amount of surface crystalline V2O5, which showed fairly strong surface acidity and significantly weakened redox ability. Calcination of a 10% V2O5/CeO2 at 873 K resulted in the formation of mainly CeVO4 on the surface, which showed low surface acidity and redox ability. The probe reaction seemed to suggest that the calcination at higher temperature might cause the decrease of surface acidity more than redox ability. Thus, the 10% V2O5/CeO2 catalyst calcined at 873 K exhibited much higher selectivity to benzaldehyde as compared to other V2O5/CeO2 catalysts studied in this work, although its activity for the conversion of toluene was relatively low.

AbstractA series of TiO2-ZrO2 composite oxides were prepared by a coprecipitation method, and were characterized by N2 adsorption, XRD, TEM, microcalorimetric adsorption of NH3 and CO2, and infrared spectra of ammonia adsorption. In comparison with the single metal oxide, amorphous composite oxides could be observed with mesoporous structure and higher BET surface area (SBET=218 m2·g−1). Although the initial adsorption heat for all these samples did not vary significantly, composite oxides possessed more Brönsted acid sites than the single oxide. With an increase in the incorporated amount of titania, the number of basic sites on the surface of composite oxides decreased. In the absence of O2, the values of selectivity for propene exceeded 90% for all these catalysts via isopropanol catalytic conversion, revealing that each of the samples had a strong surface acidity. However, in the presence of O2, 70%–85% selectivity for acetone was obtained for TiO2 and ZrO2, suggesting that redox properties were predominant over acidity. Due to the formation of composite oxides, selectivity for propene increased to about 70%, whereas selectivity for acetone decreased to about 30%, indicating that the acidity was enhanced and the redox property was weakened.

Microcalorimetry and infrared spectroscopy for ammonia adsorption have been used to study the nature, strength and number of surface acid sites of H-ZSM-5, steam de-aluminated H-Y zeolite (SDY), γ-Al2O3 and Ti(SO4)2/γ-Al2O3 catalysts for the dehydration of methanol to dimethyl ether (DME). The conversion of isopropanol was also performed as a probe reaction to characterize the acid strength. The H-ZSM-5 and SDY possessed strong Brønsted acidity and exhibited high activity for the conversion of methanol to DME at relatively low temperatures, but they did not seem to be suitable as the dehydration component of the hybrid catalyst for the direct synthesis of DME from syngas since the two zeolite catalysts produced hydrocarbons and coke from methanol at temperatures higher than 513 K. The coke was serious over the two zeolite catalysts at 553 K. The dehydration of methanol to DME on γ-Al2O3 was found to be low at the temperatures below 573 K though the DME selectivity is high. The modification of the γ-Al2O3 by Ti(SO4)2 greatly enhanced the surface Brønsted acidity and also the reaction activity for the dehydration of methanol to DME. In addition, no detectable hydrocarbon by-products and coke were formed on the Ti(SO4)2/γ-Al2O3 catalyst in the temperature range of 513–593 K. Thus, the Brønsted acid sites with suitable strength may be responsible for the effective conversion of methanol to DME with high stability.

The surface acidic and redox properties of CeO2, MoO3, mechanically mixed CeO2–MoO3 and co-precipitated Ce–Mo–O catalysts were characterized by using microcalorimetric adsorption of ammonia and isopropanol (IPA) probe reaction, and the surface properties of these catalysts were correlated with their selectivity for the oxidation of toluene to benzaldehyde and benzoic acid. With the presence of O2, IPA converted to propylene and diisopropyl ether on acidic sites while converted to acetone on redox sites. It was found that CeO2 exhibited mainly the redox property while MoO3 the surface acidity. The IPA probe reaction showed that the mechanically mixed CeO2–MoO3 exhibited the surface acidic property, similar to that of MoO3, indicating that the surface of CeO2 might be covered by MoO3 in the mixture upon the calcination at 773 K. On the other hand, the co-precipitated Ce–Mo–O catalyst showed the equivalent acidic and redox properties, and thereby the selectivity to benzaldehyde was greatly enhanced on it as compared to the other catalysts studied in this work.

The thermal decomposition of dimethoxymethane (DMM) and dimethyl carbonate (DMC) on MgO, H-ZSM-5, SiO2, γ-Al2O3 and ZnO was studied using a fixed bed isothermal reactor equipped with an online gas chromatograph. It was found that DMM was stable on MgO at temperatures up to 623 K, while it was decomposed over the acidic H-ZSM-5 with 99% conversion at 423 K. On the other hand, DMC was easily decomposed on the strong solid base and acid. The conversion of DMC was 76% on MgO at 473 K, and 98% on H-ZSM-5 at 423 K. It was even easier decomposed on the amphoteric γ-Al2O3. Both DMM and DMC were relatively stable on SiO2 possessing little surface acidity and basicity. They were even more stable on ZnO with the conversion of DMM and DMC of about 1.5% at 573 K. Thus, metal oxides with either strong acidity or basicity are not suitable for the selective oxidation of DMM to DMC, while ZnO may be used as a component for the reaction.

Pd/SiO2 and Pd–Ag/SiO2 catalysts prepared by incipient wetness impregnation method were studied by using the techniques of microcalorimetric adsorption and infrared spectroscopy for the adsorption of H2, CO and ethylene at room temperature. It is found that most sites of H2 adsorption on Pd–Ag(1:1)/SiO2 and Pd–Ag(1:4)/SiO2 are weaker than those on Pd/SiO2 though the initial heat of H2 adsorption on Pd/SiO2 is not affected by Ag. The initial heat of 135 kJ mol−1 for CO adsorption on Pd/SiO2 is the average heat produced by both bridged and linearly bonded CO on Pd while the initial heat of 117 kJ mol−1 on Pd–Ag(1:1)/SiO2 and 90 kJ mol−1 on Pd–Ag(1:4)/SiO2 are contributed by the linearly bonded CO on Pd sites modified by Ag with different Pd/Ag atomic ratios. These results suggest that the Pd–Ag/SiO2 catalysts may have well mixed Pd and Ag atoms in the Pd–Ag clusters. Strong interactions between the two types of atoms were observed. Ethylene adsorption on Pd/SiO2 at room temperature produces adsorbed ethylidyne and atomic hydrogen with the initial heat of 175 kJ mol−1. Addition of Ag may inhibit the formation of ethylidyne and promote the formation of π-species for ethylene adsorption in Pd–Ag/SiO2 catalysts. The formation of the π- and di-σ species for ethylene adsorption on the Pd–Ag(1:1)/SiO2 catalyst at room temperature generates the initial heat of 100 kJ mol−1. The initial heat of 74 kJ mol−1 produced for the adsorption of ethylene on the Pd–Ag(1:4)/SiO2 at room temperature may be attributed to the formation of only π-species on Pd with more surrounding Ag atoms. This work demonstrates how the nature and bond strength of the surface species formed on the adsorption of ethylene on Pd may be altered by using Ag as a modifier.

Polyoxymethylene dimethyl ethers (PODE) were synthesized from the reaction of paraformaldehyde with dimethoxymethane (DMM) over different acid catalysts at different conditions. Products were found to follow the Schulz-Flory distribution law. The chain propagation proceeds through the insertion of an individual segment of CH2O one by one, while the simultaneous insertion of a few CH2O segments or their assembly is unlikely. Due to the restriction of this law, it is difficult to increase the selectivity to the desired products (e.g., PODE3–4).Polyoxymethylene dimethyl ethers (PODE) were synthesized from the different reactants, e.g., paraformaldehyde and dimethoxymethane, at different reaction temperatures and the products were found to follow the Schulz-Flory distribution law.Download full-size image

Two acidic carbon materials (H-PRC and HS-C) were used as catalysts for the condensation reaction of methanol with formaldehyde to produce dimethoxymethane (DMM) in aqueous solution (hydrophilic system) and for the etherification of isopentene with methanol to produce tert amyl methyl ether (TAME) in toluene solution (lipophilic system). Microcalorimetric adsorptions of water and benzene showed that the HS-C was highly hydrophilic without the lipophilicity, while the H-PRC exhibited both the hydrophilicity and lipophilicity. Thus, the HS-C was well dispersed in aqueous solution and difficult to separate from it. On the other hand, the H-PRC was highly active, more active than the acidic resin (D008) and sulfuric acid, for the synthesis of DMM in aqueous solution. The H-PRC was also highly active, more active than the HS-C, for the etherification of isopentene with methanol to produce TAME in toluene solution, probably owing to its amphiphilic surface property as well as its strong surface acidity as measured by the microcalorimetric adsorption of NH3.The microcalorimetric adsorption of water and benzene indicated that the HS-C was highly hydrophilic while the H-PRC was amphiphilic (both hydrophilic and lipophilic).Download full-size image

The Ni2P/MgAlO catalysts with different MgO/Al2O3 ratios were prepared by the phosphidation of corresponding Ni/MgAlO catalysts with triphenylphosphine in liquid phase. It was found that the MgO/Al2O3 ratio affected the Ni2P/MgAlO catalysts significantly. The Ni2P/MgAlO catalyst with the MgO/Al2O3 ratio of 3 (w/w) exhibited the highly dispersed Ni2P particles (∼9 nm) with the highest CO uptake (344 µmol/g) and thus the highest activities for the hydrotreating reactions. However, based on the CO uptakes on the used catalysts, the TOF values for the hydrodesulphurization of dibenzothiophene as well as those for the hydrogenation of tetralin on all the Ni2P/MgAlO catalysts were respectively similar, indicating that the MgO/Al2O3 ratio did not affect the intrinsic activities of Ni2P supported on the MgAlO support for the hydrotreating reactions.Among the Ni2P/MgAlO catalysts, the one with MgO/Al2O3 weight ratio of 3 exhibited highly dispersed Ni2P particles (∼9 nm) with the highest CO uptake (344 µmol/g) and thus the highest activities for the hydrotreating reactions.Download high-res image (213KB)Download full-size image

Ni/MgAlO and K2CO3Ni/MgAlO catalysts for the hydrogenation of acetonitrile to primary amine were studied. Microcalorimetric measurements and infrared spectroscopy were used to study the adsorption of CO, H2, acetonitrile, and ethylamine onto the catalysts. It was found that the addition of K2CO3 led to an increase in the heat of adsorption of CO on Ni, due to increased surface electron density of Ni. The presence of K2CO3 weakened the strength of HNi and strengthened the bonding of CH3CN onto Ni by changing adsorptive states of CH3CN, which might be two main reasons for the decreased activity of Ni doped with K2CO3. Furthermore, the addition of K2CO3 decreased adsorptive strength of ethylamine on Ni, resulting in an increase in ethylamine selectivity. Finally, infrared spectra of CH3CN adsorbed onto the Ni surface with preadsorbed hydrogen indicated that the hydrogenation might occur preferentially on carbon atoms in CN, leading to the formation of surface species NiNCHCH3 and NiNCH2CH3.Graphical abstractThe addition of K2CO3 significantly increased the heat of adsorption of CH3CN onto Ni and changed the adsorption structures from that involving the π bond in CN to di-σ bonded CH3CN. The strong adsorption of CH3CN might be an important factor in the decreased activity of Ni doped with K2CO3 for the hydrogenation of acetonitrile to ethylamine.Download high-res image (101KB)Download full-size imageHighlights► Addition of K2CO3 increased electron density on Ni and strengthened CO adsorption. ► Addition of K2CO3 weakened H2 adsorption on Ni and decreased hydrogenation activity. ► Addition of K2CO3 weakened adsorption of ethylamine and increased its selectivity. ► Addition of K2CO3 changed adsorption structures of CH3CN on Ni. ► Addition of K2CO3 strengthened adsorption of CH3CN and decreased catalytic activity.

Di(2-ethylhexyl) hexahydrophthalate, an environmentally benign plasticizer of polyvinylchloride, could be produced through the hydrogenation of dioctyl phthalate (DOP). The hydrogenation of DOP was compared to that of toluene in this work by using supported nickel catalysts. While the surface acid/base properties significantly affected the activity of toluene hydrogenation, such effect was absent for the hydrogenation of DOP. Such different behavior might be due to the different electron charge distributions among the atoms in the two molecules. Thus, the active nickel surface area and pore size of catalysts might be the two major factors affecting the activity of hydrogenation of DOP.While the hydrogenation of aromatic ring in toluene was significantly affected by the surface acid/base properties of supported Ni catalysts, the hydrogenation of that in dioctyl phthalate (DOP) was not affected at all. Calculated Mulliken charges indicate that the difference might be caused by the different charge distributions.Download full-size imageHighlights► Hydrogenation of dioctyl phthalate (DOP) over supported nickel catalysts. ► Acidity/basicity affected the activity of hydrogenation of toluene significantly. ►Acidity/basicity did not affect the activity of hydrogenation of DOP. ►Charge distributions of reactants determined the effects of acidity/basicity.

A novel method for the preparation of acid carbon catalyst from glucose and 4-hydroxybenzenesulfonic acid (p-HBSA) was reported. Glucose was first hydrolyzed to hydroxymethylfurfural that reacted with p-HBSA (a phenol compound) to form a phenolic (PF)-like resin containing –SO3H groups. The resin was carbonized and sulfonated further in concentrated sulfuric acid at 443 K to form an amorphous carbon material with a surface area of 22 m2/g. This acidic carbon contained 3.1 mmol/g of strong surface acid sites (–SO3H), and thus exhibited good catalytic activity for the etherification of isopentene with methanol to produce tert-amyl methyl ether.

Highly loaded Co/SiO2 catalysts were prepared by a co-precipitation technique with an n-butanol drying process for Fischer–Tropsch synthesis (FTS). With the increase in cobalt loading from 20% to 80%, the FTS activity of the catalysts increased greatly. The addition of ZrO2 improved the dispersion of cobalt and promoted the adsorption of H2 and CO on cobalt. The preadsorbed H atoms significantly enhanced the adsorption of CO and C2H4, especially on cobalt promoted by ZrO2. While the adsorption of C2H4 onto clean cobalt led to the formation of ethylidyne, π- and di-σ-bonded C2H4 might form on the CO-preadsorbed 80%Co/SiO2 and 80%Co–8%ZrO2/SiO2, respectively. The presence of ZrO2 strengthened the bonding of molecularly adsorbed ethylene and increased its uptake on CO-preadsorbed cobalt, which might be why the 80%Co–8%ZrO2/SiO2 exhibited such high activity for the hydrogenation of CO to heavy hydrocarbons.Graphical abstractWhile the adsorption of C2H4 on clean cobalt surface led to the formation of ethylidyne, π and di-σ-bonded C2H4 might form on the CO-preadsorbed 80%Co/SiO2 and 80%Co–8%ZrO2/SiO2, respectively.Download high-res image (98KB)Download full-size imageResearch highlights► Highly active Co–ZrO2/SiO2 catalysts were prepared for Fischer–Tropsch synthesis. ► ZrO2 promoted the dispersion of Co and enhanced the adsorption of CO and H2 on Co. ► The preadsorbed H promoted the adsorption of CO and ethylene on Co. ► ZrO2 strengthened the bonding of adsorbed C2H4 on Co with preadsorbed CO.

Reforming of hydrocarbons and oxygenated hydrocarbons is a potential way to supply H2 for portable and household fuel cell applications. Of course, avoiding the use of toxic fuels is desirable. The extremely low toxicity of dimethoxymethane (DMM) may make it a preferred fuel for portable and household H2 sources. We found that DMM can be effectively reformed to hydrogen on specially designed complex catalysts with bifunctional characters. The complex catalysts consisted of a traditional Cu–ZnO/γ-Al2O3 for the reforming of methanol and an acidic component for the hydrolysis of DMM. The acidity of the acidic component was found to be essential for the complex catalyst. A significant amount of dimethyl ether (DME) was produced when a strong solid acid such as H-ZSM-5 was used with the Cu–ZnO/γ-Al2O3 for the reforming of DMM. On the other hand, γ-Al2O3 exhibited low activity for the hydrolysis of DMM, resulting in the low efficiency of the complex catalyst. Tests showed that the acidic carbon nanofibers (H-CNF) seemed suitable as the acidic component in the complex catalysts. In fact, the complex catalysts Cu–ZnO/γ-Al2O3–H-CNF were found to exhibit excellent performance for the reforming of DMM. The rate of H2 production from the reforming of DMM on the Cu–ZnO/γ-Al2O3–H-CNF could be as good as that from the reforming of methanol over the traditional Cu–ZnO/γ-Al2O3, whereas the reforming of DMM over the Cu–ZnO/γ-Al2O3 without an acidic component exhibited low activity and produced a significant amount of DME. Mechanistic studies showed that DME was produced from DMM on the Cu surface when no additional acidic component was present.

V–Ti–O oxides with about 4% sulfate were prepared by a co-precipitation method, which showed strong surface acidic and redox properties, and therefore exhibited good performance for the selective oxidation of methanol to dimethoxymethane (DMM) at relatively low reaction temperatures (e.g., 443 K). However, the selectivity to DMM substantially decreased when reaction temperature increased to higher than 453 K. Addition of SiO2 significantly weakened the surface acidity and redox ability of V–Ti–O, and significantly improved the selectivity to DMM above 453 K. Ninety-three percentage selectivity to DMM with 66% conversion of methanol was obtained over a Si–V–Ti–O catalyst at 483 K.

A new and facile method was developed for the preparation of mesoporous carbon materials from soluble and hydrolyzable carbohydrates with a metal chloride template. The preparation procedure and related mechanism were demonstrated using fructose and ZnCl2 as examples of the carbon precursor and template, respectively. Since both fructose and ZnCl2 are soluble in water, they can be mixed homogeneously initially. Fructose was first hydrolyzed to hydroxymethylfurfural, which was then polymerized to form a resin; both reactions were catalyzed by the acidic ZnCl2. During the carbonization, ZnCl2 might act as an activation agent promoting the carbonization of cured resin and a template for the formation of mesopores. Mesoporous carbon materials with high surface areas (1400–2000 m2 g−1), large pore volumes (1.44–2.72 cm3 g−1) and 100% mesopores with an average size of 3–7 nm can be prepared by using this simple and cost-effective method. The materials could be used as adsorbents and catalyst supports for relatively large molecules.

Ni2+ and H2PO2− with a molar ratio of 1/3 were heated at 423 K in a eutectic mixture composed of choline chloride and urea, resulting in the formation of a mesoporous and amorphous material with surface area of about 210 m2 g−1. Heat treatment of this material in H2 at 673 K led to the formation of crystalline Ni2P (25%) supported on amorphous and mesoporous Ni3(PO4)2-Ni2P2O7 (shortened as NiPO) with a surface area of about 130 m2 g−1. The NiPO was presumably produced from the reaction of unreduced Ni2+ with PO43− formed from the oxidation of H2PO2− in the eutectic mixture, which might also act as a template for the formation of mesopores in NiPO. The catalyst 25% Ni2P/NiPO exhibited a quite high uptake for the adsorption of CO (38 μmol g−1), and thus it is quite active for the hydrodesulfurization of dibenzothiophene, hydrodenitrogenation of quinoline and hydrogenation of tetralin in a model diesel.

Dimethoxymethane was synthesized from the direct oxidation of methanol with high conversion and selectivity over specially designed bifunctional V2O5/TiO2 catalysts with redox and enhanced acidic character, in which the surface acidity played an essential role for inhibiting the formation of formaldehyde through the enhanced condensation reaction of formaldehyde with methanol to produce dimethoxymethane.

Nanoparticles of Ni2P were simply prepared by a solid phase reaction of H2PO2− with Ni2+ in N2 at relatively low temperatures, which exhibited high activity for the hydrodesulfurization of dibenzothiophene and hydrodenitrogenation of quinoline.