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Three supported Ir/TiO2 catalysts, containing anatase TiO2 nanocrystals with predominantly exposed {101}, {100}, and {001} planes, were subjected to various pre-treatments (H2 reduction at different temperatures and O2 re-oxidation) and then tested in the vapor phase selective hydrogenation of crotonaldehyde. The pre-treatments significantly altered the Ir-TiOx interactions, including the morphologies and electronic properties of the Ir species and their surface acidity. These interactions were also closely related to the crystal planes of TiO2, which further supported the observed reaction behaviors of the various Ir/TiO2 catalysts. The best performance was obtained using the Ir/TiO2-{101} catalyst pre-reduced at 300 °C, owing to its higher Ir0 surface concentration and moderate surface acidity compared to the other catalysts. Moreover, these findings indicated the synergistic role of the Ir-TiOx interface in the reaction, as the interfacial sites were responsible for the adsorption/activation of H2 and the C=O bond in the crotonaldehyde molecule. However, pre-reduction at 400 °C resulted in partial encapsulation of the Ir particles by TiOx via strong metal-support interactions, which is unfavorable for the catalytic reaction owing to the loss of Ir-TiOx interfacial sites.

Cu–ZnO–Al2O3 catalysts are used as the industrial catalysts for water gas shift (WGS) and CO hydrogenation to methanol reactions. Herein, via a comprehensive experimental and theoretical calculation study of a series of ZnO/Cu nanocrystals inverse catalysts with well-defined Cu structures, we report that the ZnO–Cu catalysts undergo Cu structure-dependent and reaction-sensitive in situ restructuring during WGS and CO hydrogenation reactions under typical reaction conditions, forming the active sites of CuCu(100)-hydroxylated ZnO ensemble and CuCu(611)Zn alloy, respectively. These results provide insights into the active sites of Cu–ZnO catalysts for the WGS and CO hydrogenation reactions and reveal the Cu structural effects, and offer the feasible guideline for optimizing the structures of Cu–ZnO–Al2O3 catalysts., Identification of active sites of a catalyst is the Holy Grail in heterogeneous catalysis. Here, the authors successfully identify the CuCu(100)- hydroxylated ZnO ensemble and CuCu(611)Zn alloy as the active sites of Cu-ZnO catalysts for water gas shift and CO hydrogenation reactions, respectively.

The Cu-based catalysts have been widely employed in the hydrogenation of CO2-derived ethylene carbonate (EC) to methanol (MeOH) and ethylene glycol (EG), but still suffered from some problems such as excess hydrogen/ester ratio, unsatisfactory MeOH selectivity and catalyst stability & deactivation. Herein, a MoOx-promoted Cu/SiO2 catalyst, which was prepared via a one-pot modified hydrothermal method and derived from copper phyllosilicate precursors, exhibited superior catalytic performance (89% MeOH yield and 99% EG yield) and good stability (>150 h) at a H2/EC ratio (20). Remarkably, the turnover frequency (TOF) and space time yield of MeOH (STYMeOH) reached up to 17.5 h−1 and 0.207 g⋅gcat−1⋅h−1, respectively, which are among the highest values in the literature data. The characterization results and kinetic studies revealed that modification of Cu species by MoOx obviously changed the electronic properties of Cu species, reduced the activation energy and enhanced the Cu+/(Cu0 + Cu+) ratios. Such modification may lead to possible formation of Cu-O-Mo bond between Cu species and MoOx species located on the periphery of Cu-MoOx interface, which might strengthen the adsorption and activation of EC, stabilize the Cu nanoparticles, and thus improve the selectivity to MeOH and catalyst stability. In addition, MoOx decoration had obvious effect on the strength and quantity of the surface acid sites.

Several Pd catalysts supported on CeO2 with different morphologies (i.e. CeO2 rods (r-CeO2), cubes (c-CeO2) and polyhedra (p-CeO2)) were tested for the CO2 hydrogenation into formate. Remarkable morphology - dependent Pd-CeO2 interaction was observed, which was related to the oxygen vacancies in the CeO2. The r-CeO2 with the highest concentration of oxygen vacancy resulted in smaller Pd particles and more positively-charged Pd species in the Pd/r-CeO2 catalyst. The best performance was obtained over the Pd/p-CeO2 catalyst, giving a turnover frequency of 746 h−1 at 40 °C. The enhanced activity was due to the highest content of metallic Pd species in the catalyst, which was responsible for the facile activation of H2. Moreover, in situ spectroscopic results revealed that the hydrogenation of the carbonaceous intermediates was the rate - determining step. This work demonstrates oxide morphology engineering as a powerful strategy in developing efficient Pd - based catalysts for CO2 hydrogenation.

Strong metal-support interactions (SMSI) is an important concept in heterogeneous catalysis. Herein, we demonstrate that the Au-TiO2 SMSI of Au/TiO2 catalysts sensitively depends on both Au nanoparticle (NP) sizes and TiO2 facets. Au NPs of ca. 5 nm are more facile undergo Au-TiO2 SMSI than those of ca. 2 nm, while TiO2 {001} and {100} facets are more facile than TiO2 {101} facets. The resulting capsulating TiO2-x overlayers on Au NPs exhibit an average oxidation state between +3 and +4 and a Au-to-TiO2-x charge transfer, which, combined with calculations, determines the Ti:O ratio as ca. 6:11. Both TiO2-x overlayers and TiO2-x -Au interface exhibit easier lattice oxygen activation and higher intrinsic activity in catalyzing low-temperature CO oxidation than the starting Au-TiO2 interface. These results advance fundamental understanding of SMSI and demonstrate engineering of metal NP size and oxide facet as an effective strategy to tune the SMSI for efficient catalysis.

Supported Ir/TiO2 catalysts with the anatase TiO2 nanocrystals exposing {1 0 1}, {1 0 0} and {0 0 1} planes were tested for selective hydrogenation of crotonaldehyde. The Ir/TiO2-{1 0 1} catalyst dominantly exposing {1 0 1} plane gave a initial reaction rate of 166.1 μmol gIr-1 s−1 at 80 °C and a turnover frequency of crotyl alcohol formation of 0.022 s−1, which is 5 and 7 times respectively higher than those obtained on the Ir/TiO2-{0 0 1} catalyst dominantly exposing {0 0 1} plane even though they have similar Ir particle sizes (ca. 1.3 nm). The reaction behaviors were related to the surface oxygen vacancy, which served as surface acid sites and provide adsorption sites for C O bond in the CRAL molecule. Therefore, the higher concentration of oxygen vacancy in the Ir/TiO2-{1 0 1} accounted for the improved performance compared to the Ir/TiO2-{0 0 1}. However, strong adsorption of crotonaldehyde and/or products on the catalyst surface, as well as the CO poisoning via decarbonylation of crotonaldehyde, were the main reasons for the catalyst deactivation.

A series of Ir/BN catalysts with same Ir contents (2 wt%) were calcined at different temperatures and tested for gas phase selective hydrogenation of crotonaldehyde. It was found that the thermal treatment exerted significant impacts on the structural and electronic properties of the 2Ir/BN catalysts. The catalyst calcined at 500 °C (2Ir/BN-5) showed the best performance, with a steady state of conversion of ca. 21% and a crotyl alcohol selectivity of ca. 83% at reaction temperature of 80 °C. Kinetic analysis indicated that the enhanced activity on the 2Ir/BN-5 catalyst was related to its higher surface coverage of crotonaldehyde because of the presence of small Ir particles (with a mean diameter of 3.4 nm) compared to those in the catalyst calcined at 600 °C (2Ir/BN-6, with a mean diameter of 4.4 nm). Also, the surface of the Ir species in the 2Ir/BN-5 catalyst are more electron-enriched compared to that in the 2Ir/BN-6, which suppressed the adsorption of C=C bond and thus improves the selectivity to CROL.

Various Cu2O nanocrystals (NCs), including cubes exposing {100} crystal planes (c-Cu2O), octahedra exposing {111} crystal planes (o-Cu2O), and rhombic dodecahedra exposing {110} crystal planes (d-C...

A series of Co–Cr–O mixed oxides with different Co/Cr molar ratios are synthesized and tested for the total oxidation of propane. The reaction behaviors are closely related to the structural features of the mixed oxides. The catalyst with a Co/Cr molar ratio of 1:2 (1Co2Cr) and a spinel structure has the best activity (with a reaction rate of 1.38 μmol g−1 s−1 at 250 °C), which is attributed to the synergistic roles of its high surface acidity and good low-temperature reducibility, as evidenced by the temperature-programmed desorption of ammonia, reduction of hydrogen, and surface reaction of propane. Kinetic study shows that the reaction orders of propane and oxygen on the 1Co2Cr catalyst (0.58 ± 0.03 and 0.34 ± 0.05, respectively) are lower than those on the 2Co1Cr catalyst (0.77 ± 0.02 and 0.98 ± 0.16, respectively) and 1Co5Cr (0.66 ± 0.05 and 1.30 ± 0.11, respectively), indicating that the coverages of propane and oxygen on 1Co2Cr are higher than those on the other catalysts due to its higher surface acidity and higher reducibility. In addition, in-situ diffuse reflectance infrared spectroscopic investigation reveals that the main surface species on 1Co2Cr during the reaction are polydentate carbonate species, which accumulate on the surface at low temperatures (

A series of Pt/Cr1.3Fe0.7O3 catalysts were tested for CO oxidation, and the activities are improved by the presence of H2O. Such improvement is more significant on the single atom 0.2Pt/Cr1.3Fe0.7O3 than on the 2Pt/Cr1.3Fe0.7O3 containing Pt nanoparticles, with turnover frequencies of 0.396 and 0.094 s−1 at 60 °C under 1% CO + 1% O2 + 10% CO2 + 10% H2O, respectively. In-situ diffuse reflectance infrared Fourier transform spectroscopic study on these catalysts suggests that the promoting effect of H2O is due to the facile reaction between adsorbed CO and surface hydroxyl groups via H2O dissociation. Kinetic investigation reveals that the 0.2Pt/Cr1.3Fe0.7O3 gives a higher intrinsic rate constant than the 2Pt/Cr1.3Fe0.7O3 (9.23 × 10−5 versus 4.50 × 10−5 mol g−1 s−1 at 60 °C) for the formation of formate intermediate due to its weaker CO adsorption strength, which explains the more significant H2O promotion on the single atom Pt catalyst.

A series of MoOx-promoted Ir/TUD-1 catalysts were tested for liquid phase selective hydrogenation of crotonaldehyde. The promoted catalysts showed higher activity and selectivity than the unpromoted one, with the best performance being obtained on an Ir-0.1Mo/TUD-1 (with a crotyl alcohol yield of 86.7% and a turnover number of 325.7 h−1). The large pore sizes of the TUD-1 is beneficial to the diffusion of the reactant and thus the supported catalyst is more active than that supported on the commercial SiO2. The characterization results revealed decoration of Ir particles by MoOx, which altered the morphologies and electronic properties of the catalysts. Such decoration resulted in the generation of Ir-MoOx interfacial sites, which altered the adsorption and activation of crotonaldehyde molecule and brought up enhanced activity and selectivity. However, at high MoOx content, the Ir surface was fully covered by MoOx, which results in strong adsorption of crotonaldehyde and fewer surface Ir atoms for H2 dissociation and thus declined activity.

The interaction of hydrogen with reduced ceria (CeO2−x) powders and CeO2−x(111) thin films was studied using several characterization techniques including TEM, XRD, LEED, XPS, RPES, EELS, ESR, and TDS. The results clearly indicate that both in reduced ceria powders as well as in reduced single crystal ceria films hydrogen may form hydroxyls at the surface and hydride species below the surface. The formation of hydrides is clearly linked to the presence of oxygen vacancies and is accompanied by the transfer of an electron from a Ce3+ species to hydrogen, which results in the formation of Ce4+, and thus in oxidation of ceria., Oxidizing hydride: The incorporation of hydride species into reduced ceria causes oxidation of the oxide. Accompanying changes in the electronic structure of the oxide are investigated, as well as the thermal stability of the hydride species.

Pt catalysts supported on a series of CrxFe2-xO3 composite oxides with different Cr/Fe molar ratios were prepared and tested for CO oxidation. The Pt/Cr1.3Fe0.7O3 catalyst possesses the best performance (with a turnover frequency of ca. 0.2 s −1 at 80 °C under 1% CO + 1% O2 condition), due to its best reducibility which was related to the solid solution structure of the support. The catalyst also shows good stability in the presence of both 10% CO2 and 10% H2O. Detailed kinetic results and staged reaction indicate that CO2 and H2O play opposite roles in the reaction. The inhibiting role of CO2 is due to competitive adsorption of CO2 with CO and the formation of carbonate species. However, the addition of H2O could effectively decompose the carbonate and sustain the catalyst stability. Moreover, the promoting role of H2O could be mainly attributed to the weakened strength of CO adsorption and the fast interfacial reaction between CO and the surface hydroxyl groups formed via H2O dissociation, as revealed by the X-ray photoelectron spectroscopy, CO temperature-programmed desorption and the kinetic results.

Catalytic propane combustion was performed on a series of supported Pt/AlF3 catalysts. These catalysts are very active and stable in the reaction, and the 0.2Pt/AlF3 catalyst gives the highest specific reaction rate of 207.3 μmol gPt−1 s−1 at 220 °C. The 1Pt/AlF3 is much more active than the reference Pt/Al2O3 catalyst, due to its higher content of metallic Pt species than that in the Pt/Al2O3. Furthermore, turnover frequency (TOF) based on Pt dispersion increases with the surface concentration of metallic Pt0 in the catalyst, suggesting these species might be the active sites. Furthermore, synergistic roles of metallic and oxidized Pt species are found, as the TOFs calculated based on surface Pt0 concentration reaches a maximum at the Pt0/Pt2+ molar ratio of about 1. Such optimal Pt0/Pt2+ ratio implies the requirement of Pt0 Pt2+ pair in the reaction, probably due to the activation and cleavage of C H bond on metallic Pt atom and the sequential oxidation on the oxidized Pt atoms.

Cu-ZnO-Al2O3 catalysts are used as the industrial catalysts for water gas shift (WGS) and CO hydrogenation to methanol reactions. Herein, via a comprehensive experimental and theoretical calculation study of a series of ZnO/Cu nanocrystals inverse catalysts with well-defined Cu structures, we report that the Cu-ZnO catalysts undergo Cu structure-dependent and reaction-sensitive in situ restructuring during WGS and CO hydrogenation reactions under typical reaction conditions, forming the active sites of CuCu(100)-hydroxylated ZnO ensemble and CuCu(611)Zn alloy, respectively. These results conclude the long-existing debates and provide the feasible guideline for optimizing the structures of Cu-ZnO-Al2O3 catalysts.

The study reports the first attempt to address the interplay between surface and bulk in hydride formation in ceria (CeO2) by combining experiment, using surface sensitive and bulk sensitive spectroscopic techniques on the two sample systems, i.e., CeO2(111) thin films and CeO2 powders, and theoretical calculations of CeO2(111) surfaces with oxygen vacancies (Ov) at the surface and in the bulk. We show that, on a stoichiometric CeO2(111) surface, H2 dissociates and forms surface hydroxyls (OH). On the pre‐reduced CeO2−x samples, both films and powders, hydroxyls and hydrides (Ce−H) are formed on the surface as well as in the bulk, accompanied by the Ce3+ ↔ Ce4+ redox reaction. As the Ov concentration increases, hydroxyl is destabilized and hydride becomes more stable. Surface hydroxyl is more stable than bulk hydroxyl, whereas bulk hydride is more stable than surface hydride. The surface hydride formation is the kinetically favorable process at relatively low temperatures, and the resulting surface hydride may diffuse into the bulk region and be stabilized therein. At higher temperatures, surface hydroxyls can react to produce water and create additional oxygen vacancies, increasing its concentration, which controls the H2/CeO2 interaction. The results demonstrate a large diversity of reaction pathways, which have to be taken into account for better understanding of reactivity of ceria‐based catalysts in a hydrogen‐rich atmosphere., A first attempt to establish the interplay between surface and bulk in hydride formation in ceria (CeO2) has been carried out by combining experiment, using surface sensitive and bulk sensitive spectroscopic techniques on the two sample systems, i.e., CeO2(111) thin films and CeO2 powders, and theoretical calculations of CeO2(111) surfaces with oxygen vacancies (Ov) at the surface and in the bulk.

A series of supported CoCr2O4/TUD-1 catalysts with different loadings were prepared and tested for catalytic combustion of dichloromethane, in order to investigate the effect of particle size on the catalyst properties and related catalytic behaviors. It was found that the supported catalyst with low content of CoCr2O4 had smaller CoCr2O4 particles compared to that with high content, as revealed by the XRD results. Consequently, the changes in particle size altered the surface composition of the catalyst, as the small particles contained higher content of surface Cr6+ species compared to the large ones. The enrichment of Cr6+ species improved catalyst reducibility and surface acidity, which synergistically governed the observed catalytic behaviors. As a reuslt, the 5CoCr2O4/TUD-1 catalyst had the highest reaction rate of 64.8 × 10−7 molDCM g−1CoCr2o4s−1, due to its best reducibility and highest surface acidity.

A series of MoOx-promoted Ir/BN catalysts were tested for liquid phase selective hydrogenation of crotonaldehyde. The MoOx-promotion could significantly improve the reactivity up to 5-fold. Such improvement was mainly due to the formation of Ir-MoOx interfacial sites in the promoted catalyst, which accelerated the adsorption and activation of crotonaldehyde molecule as evidenced by a much lower activation energy (18.9 kJ mol−1 on the 0.3Mo-3Ir/BN versus 38.4 kJ mol−1 on the 3Ir/BN). The kinetic results revealed negative reaction order of crotonaldehyde (up to -1.1) and high reaction order of H2 (up to 2.2), indicating the high coverage of crotonaldehyde on the catalyst surface suppressed the adsorption of H2 due to its low solubility in the liquid phase. Therefore, the adsorption and activation of H2 on the catalyst might be the rate determining step. However, the preferred adsorption of crotonaldehyde on the Ir-MoOx interface alleviated the suppression of H2 adsorption, which was another reason for the higher activity.

Pt supported on CoFe2O4 and NiFe2O4 spinel oxides were much more active for low temperature CO oxidation compared to those supported on monometallic oxides (i.e. Co3O4, Fe2O3 and NiO). The Pt/CoFe2O4 catalyst gave the best performance, with a turnover frequency of 0.27 s−1 at 50 ℃, which was three times as high as that on the Pt/Fe2O3. The interaction between Pt and the spinel oxide facilitated the activation of the oxygen species as evidenced by the H2 temperature programmed reduction results, and weakened the adsorption strength of CO on the Pt atoms as revealed by the in situ diffuse reflectance infrared Fourier transform spectroscopy results and kinetic investigation. These facts accounted for the enhanced reactivity. Moreover, the catalysts exhibited excellent water tolerance, which maintained activity even under 10 vol.% water vapor in the feed stock. Therefore, these catalysts are promising for practical applications.

CeO2, which was used as support to prepare mesoporous Ni/CeO2 catalyst, was prepared by the hard-template method. The prepared NiO/CeO2 precursor and Ni/CeO2 catalyst were studied by H2–TPR, in-situ XPS, and in-situ FT-IR. The catalytic properties of the prepared Ni/CeO2 catalyst were also investigated by CO2 catalytic hydrogenation methanation. H2–TPR and in-situ XPS results showed that metal Ni species and surface oxygen vacancies could be formed by H2 reduction. In-situ FT-IR and in-situ XPS results indicated that CO2 molecules could be reduced by active metal Ni species and surface oxygen vacancies to generate active CO species and promote CO2 methanation. The Ni/CeO2 catalyst presented the high CO2 methanation activity, and CO2 conversion and CH4 selectivity reached 91.1% and 100% at 340 °C and atmospheric pressure.

Ordered Cr2O3 nanorods (Cr2O3-R) and Cr2O3 nanoparticles (Cr2O3-P) were prepared by a hard template method with SBA-15 and a deposition–precipitation method, respectively. These catalysts were tested for the fluorination of 2-chloro-1,1,1-trifluoroethane (HCFC-133a) to synthesize 1,1,1,2-tetrafluoroethane (HFC-134a). It was found that both catalysts were very selective, with a HFC-134a selectivity of 98 %. However, the Cr2O3-R catalyst had an area specific reaction rate of 0.012 μmol m−2 s−1 at 320 °C, which was much higher than that on the Cr2O3-P (0.005 μmol m−2 s−1). The enhanced activity of the Cr2O3-R was attributed to its higher content of Cr(VI) species compared to that in the Cr2O3-P, which was evidenced by the hydrogen temperature-programmed reduction and X-ray photoelectron spectroscopy results. Besides, the Cr2O3-R catalyst had a higher surface acid density (0.076 mmol m−2) than the Cr2O3-P (0.068 mmol m−2), which could be another reason for its better performance.

Catalytic selective hydrogenation of α,β-unsaturated aldehydes to α,β-unsaturated alcohols is very important in the synthesis of various fine chemicals. However, the development of highly efficient catalyst systems is challenging because of the low selectivity and severe deactivation of the currently employed catalysts such as Pt and Au. In this work, a series of CrOx- and FeOx-promoted Ir/SiO2 catalysts were prepared by a sequential impregnation method and tested for gas phase selective hydrogenation of crotonaldehyde. It was found that the addition of promoters could greatly enhance the catalytic performance. The Ir/SiO2 catalyst promoted with combined CrOx–FeOx with a (Cr + Fe)/Ir ratio of 0.05 showed the highest steady state crotyl alcohol yield of 64.5% at a selectivity of 86%, which is 4-fold higher than that of the unpromoted Ir/SiO2 (15.5%) catalyst. Such an enhancement was due to the formation of new active sites generated at the Ir–CrOx and/or Ir–FeOx interfaces. Also, catalysts with low loadings of promoters showed excellent stability due to their appropriate electronic properties, while the catalyst with a high loading of promoters deactivated quickly due to the strong adsorption of products on the surface.

A series of CrxFe2-xO3 mixed oxides were tested for catalytic combustion of dichloromethane. The best performance was obtained on a Cr0.8Fe1.2O3 catalyst (with a reaction rate of 3.11 mmol g−1 h−1 at 250 °C), which is higher than most of the results in literature. The reaction behavior was synergistically governed by the reducibility and surface acidity of the catalyst, which could be tuned by the compositions of Cr and Fe species in the mixed oxide. As a result, the Cr0.8Fe1.2O3 catalyst with an optimal combination of reducibility and surface acidity accounted for the best performance.

The addition of V2O5 in the Pt/SiO2 catalysts greatly improves their activities for total oxidation of propane. The much higher activity on the catalyst with a Pt content of 2 wt.% and a V content of 10 wt.% (2 Pt-10 V/SiO2) (153.2 μmol gPt−1 s−1 at 200 °C) than that on the 2 Pt/SiO2 (9.8 μmol gPt−1 s−1) is due to the enhanced reducibility and surface acidity by the V2O5 promotion. Kinetic investigations reveal that the propane coverage on the 2 Pt-3 V/SiO2 is higher than that on the 2 Pt/SiO2, due to the presence of additional acid sites by V2O5 promotion. The rate determining step is the activation of propane on the partially oxygen covered Pt pair sites (*-O*), on which propane could be activated on the metallic Pt atom and react with oxygen on the oxidized Pt species. Additional Pt-V interfacial active sites may exist in the V-promoted catalyst, on which propane adsorbed on VOx could react with oxygen on the Pt oxide.

Three CuO–MnOx–CeO2 catalysts with different impregnation sequences (i.e. MnOx/CuO/CeO2, CuO/MnOx/CeO2 and CuO–MnOx/CeO2) were prepared and the effects of impregnation sequences on the structures and catalytic behaviors of these catalysts were investigated. It was found that the MnOx/CuO/CeO2 possessed the largest amount of oxygen vacancies but the lowest reducibility; the CuO/MnOx/CeO2 had the largest Cu+ contents but the lowest amount of oxygen vacancies; the CuO–MnOx/CeO2 catalyst had the highest CuO dispersion and the best reducibility, along with moderate amount of oxygen vacancies and Cu+ contents on the surface. The kinetic studies revealed that the apparent activation energies of CO oxidation over the CuO–MnOx/CeO2, MnOx/CuO/CeO2 and CuO/MnOx/CeO2 were 49.5, 51.8 and 73.8 kJ mol−1, in order, and the activities followed an order of CuO–MnOx/CeO2 > MnOx/CuO/CeO2 > CuO/MnOx/CeO2. The highest performance of the CuO–MnOx/CeO2 was ascribed to the highly dispersed CuO species and the mobility of lattice oxygen.

A series of K-promoted Pt/Al2O3 catalysts were tested for CO oxidation. It was found that the addition of K significantly enhanced the activity. A detailed kinetic study showed that the activation energies of the K-containing catalysts were lower than those of the K-free ones, particularly for catalysts with high Pt contents (51.6 kJ/mol for 0.42K-2.0Pt/Al2O3 and 63.6 kJ/mol for 2.0Pt/Al2O3). The CO reaction orders were higher for the K-containing catalysts (about −0.2) than for the K-free ones (about −0.5), with the former having much lower equilibrium constants for CO adsorption than the latter. In situ Fourier-transform infrared spectroscopy showed that surface CO desorption from the 0.42K-2.0Pt/Al2O3 catalyst was easier than from 2.0Pt/Al2O3. The promoting effect of K was therefore caused by weakening of the interactions between CO and surface Pt atoms. This decreased coverage of the catalyst with CO and facilitated competitive O2 chemisorption on the Pt surface, and significantly lowered the reaction barrier between chemisorbed CO and O2 species.

A Ru–Ir/ZnO catalyst with metal loadings of 3% Ru and 3% Ir was reduced at different temperatures (150 to 400 °C) and tested for vapor-phase selective hydrogenation of crotonaldehyde at 80 °C. It was found that with increasing reduction temperature, the crotonaldehyde conversion over the catalysts first increased and then decreased. A conversion of 93.5% and the selectivity to crotyl alcohol of 86.6% was observed after 10 h reaction on a Ru–Ir/ZnO catalyst reduced at 200 °C. Various characterizations such as X-ray photon spectroscopy (XPS) and ammonia temperature-programmed desorption (NH3-TPD) results demonstrated that moderate interaction between the C O bond and the M0 (M = Ru, Ir or Ru–Ir alloy) due to the proper charge density of M0, and surface acidity of the catalysts played decisive roles in the enhanced activity and selectivity obtained on the catalyst. In addition, the deactivation of the catalyst was due to the carbon deposit (including organic compounds) on the catalyst surface, as evidenced by Raman spectroscopy and temperature-programmed oxidation over the spent catalyst. Also, the strong adsorption of CO on the catalyst surface generated by a decarbonylation reaction could be another reason for catalyst deactivation, as evidenced by a CO poisoning experiment.

A series of Al-substituted La1−xAlxMnO3 (x = 0 − 0.3) catalysts were prepared using a sol–gel method and tested for 1,2-dichloroethane oxidation in order to investigate the effects of Al-doping and thermal treatment on the catalyst structures and catalytic behaviors. It was found that both Al-doping and thermal treatment had great influence on the activities of the catalysts, and the highest activity was obtained on a La0.8Al0.2MnO3 catalyst calcined at 700 °C, with a T50 of 295 °C. The enhanced activity could be attributed to synergetic effects of its high surface area, high reducibility and surface acidity, as evidenced by various characterizations such as H2 temperature-programmed reduction and NH3 temperature-programmed desorption. However, comparisons of the areal specific reaction rates revealed that the catalysts calcined at 900 °C had much higher rates than the ones calcined at 500 and 700 °C, suggesting that structural properties of the catalysts exerted much stronger influence on the catalytic performance than the surface area. It was also evidenced that the reducibility of the catalyst had a dominant role in determining the intrinsic activity, which was closely related to the presence of high valent Mn4+ species in the catalyst as induced by the introduction of Al in the catalyst.

The objective of this research is to develop amine-grafted mesocellular silica foams (MCFs) based CO 2 sorbents. The template of the as-synthesized MCFs was removed by calcination or ethanol extraction method. The obtained template-free MCFs were grafted with 3-aminopropyltriethoxysilane (APS) or 3-(2-aminoethylamino)-propyl-dimethoxymethylsilane (APMS). These new composite sorbents were characterized by nitrogen adsorption/desorption, Fourier transform infrared spectroscopy (FTIR), and thermal gravimetric analysis (TGA). The infrared results indicate that more silanol groups were preserved on solvent-extracted MCF than that on calcined MCF. CO 2 capture performances of the sorbents were evaluated using a fixed-bed reactor equipped with an online mass spectrometer (MS). Experimental results show that the solvent-extracted MCF grafted with APMS exhibited a higher CO 2 adsorption capacity (1.54 mmol/g) under the condition of 10.0% (v/v) CO 2 in N 2 at 60 °C. It was also found that the APMS-grafted sorbents are more capable in CO 2 sorption than APS-grafted ones possibly due to the higher amine content of the formers, and the CO 2 uptake can be further enhanced to 2.02 mmol/g in the presence of moisture. Cyclic CO 2 adsorption–desorption test results indicate that the composite sorbents are stable and regenerable.

Gas-phase epoxidation of 3,3,3-trifluoropropylene (TFP) was conducted on a series of Au/Cu TiO 2 catalysts with different Cu contents with N 2 O as the oxidant. These catalysts were effective for this reaction. The best catalytic performance was obtained on a catalyst containing 4.6 wt.% of Au and 0.9 wt.% of Cu (4.6Au/0.9Cu TiO 2 ), with a steady-state 3,3,3-trifluoropropylene oxide (TFPO) formation rate of 72.4 g TFPO h - 1 kg cat - 1 , which was much higher than that on a 2.1Au/TiO 2 catalyst ( 22.1 g TFPO h - 1 kg cat - 1 ). The enhancement was attributed to the higher Au content in the Cu-promoted catalyst and small Au particle size and more importantly to the complicated synergy between the Au Cu TiO 2 interaction which might be the active sites for epoxidation. Also, high selectivity to TFPO up to 88% was obtained on the Cu-promoted catalyst, due to the proper electronic structure induced by the interaction between Au and low valent Cu species. Catalyst deactivation was due to the significant growth of Au particles and loss of Au Cu TiO 2 interface because of the segregation of Cu species during the reaction.

Using the method of stochastic differential equations to analysis two aircrafts and to establish the aircraft flight collision risk model. First the relative position and speed of the aircraft on the joint distribution density should be confirmed, and convert it into a Gaussian density to simplify the calculation of nonlinear filtering theory, and then use the method of stochastic differential equation to establish flight collision risk model, and also includes the introduction of how the CNS performance of random factors, human factors and avoidance system performance affect the flight collision. After verifying the collision risk in the example, the results show that the model is feasible.

The objective of this research is to develop a new type of CO2 sorbent. The sorbents were synthesized with mesoporous ethane–silica nanotubes (E–SNTs) and tetraethylenepentamine (TEPA). They were characterized by nitrogen adsorption/desorption, thermogravimetric analysis, and infrared spectroscopy. A fixed-bed reactor equipped with an online mass spectrometer was used to test the CO2 capture performances of the sorbents. It was found that 75 °C is the optimal CO2 adsorption temperature for amine-impregnated E–SNT sorbents. The highest CO2 sorption capacities achieved with E–SNTs with 50 wt % TEPA loading (E–SNTs–50%) without and with uses of water vapor are 3.58 and 4.74 mmol/g, respectively, under the conditions of a 10.0% CO2/N2 mixture at 75 °C. Cyclic CO2 adsorption–desorption test results indicate that the new composite sorbents are stable and regenerable.

The co-adsorption of hydrogen and CO on Pt film was studied by in-situ attenuated total reflection Infrared (ATR-IR) Spectroscopy. It was found that the adsorption of CO on Pt is much stronger than that of hydrogen, and the co-adsorbed hydrogen species lead to dramatic red shifts of both linear and bridged-adsorbed CO peaks. The more hydrogen species adsorbed on Pt surface, the more red shifts of CO frequencies were observed. Based on the results obtained from the well-designed experiments, it is deduced that H may act as an electron donor on Pt surface and negative charge is transferred from H to Pt. Thus, the surface charge properties of Pt film were changed, which enhances the d–π∗ backdonation effect between Pt and CO and consequently leads to dramatic red shifts of CO peaks. The density functional theory (DFT) calculations based on simple models confirmed the charge transfer effect between hydrogen and Pt. This study also shows that ATR-IR technique is a powerful tool to investigate the gas–solid interface.

A series of CuO/Ce 1− x Cu x O 2− δ catalysts were prepared, and corresponding Ce 1− x Cu x O 2− δ catalysts were obtained with nitric acid treatment. X-ray diffraction and Raman spectroscopic results revealed the presence of surface CuO species and Cu x Ce 1− x O 2− δ solid solution in the catalysts. CO oxidation testing found that the CO conversion was proportional to the concentrations of chemisorbed CO and oxygen vacancies in the CuO/Ce 1− x Cu x O 2− δ catalysts, suggesting synergetic effects of the surface CuO species and Cu x Ce 1− x O 2− δ solid solution on the reactivity, as the former provided sites for CO chemisorption and the latter promoted reducibility of the catalyst for oxygen activation. Kinetic studies showed that the apparent activation energy was 42 kJ mol −1 for CuO/Ce 1− x Cu x O 2− δ and 95 kJ mol −1 for Ce 1− x Cu x O 2− δ . The power-law rate expression was r CO = k 1 P CO 0.74 P O 2 0 for CuO/Ce 1− x Cu x O 2− δ and r CO = k 2 P CO 1.04 P O 2 0 for the Ce 1− x Cu x O 2− δ catalyst, indicating that the reaction pathway followed a Mars–van Krevelen type mechanism.

The adsorption and desorption of hydrogen on Ir/SiO2 catalyst were studied by using in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) combined with curve-fitting analysis. The results indicate that there are three different surface species formed on the catalyst that correspond to the peaks at 1950, 2010, and 2035 cm−1, respectively, when exposed in H2 flow at 130 °C. These surface species display different adsorption and desorption trends. Surface hydride forms after the catalyst is cooled to 80 °C and it disappears after the catalyst is heated to 130 °C again. This study may help us understand the interaction between hydrogen and noble metals and thus give more insights to heterogeneous catalytic mechanism involving hydrogen and hydrogen storage using metal materials.

A PdO/Ce1−xPdxO2−δ catalyst containing surface PdOx (x = 1–2) species and Ce1−xPdxO2−δ solid solution was prepared by a solution combustion method. It was found that the surface PdOx species could be removed by nitric acid treatment. Also, partial Pd4+ cations in the CeO2 lattice migrated to the surface to form surface PdOx species after high temperature calcination (500 °C). The catalyst was tested for catalytic CO and CH4 oxidation. For CO oxidation, the specific reaction rate of the surface PdOx species ( 673 .4 μ mol CO g Pd − 1 s − 1 ) was 249 times as high as that of the Ce1−xPdxO2−δ solid solution ( 2 .7 μ mol CO g Pd − 1 s − 1 ), due to the fact that the surface PdOx species provided CO chemisorption sites. While for CH4 oxidation, the specific reaction rate of the Ce1−xPdxO2−δ solid solution ( 7 .5 μ mol CH 4 g Pd − 1 s − 1 ) was higher than that of the PdO/Ce1−xPdxO2−δ catalyst ( 2 .8 μ mol CH 4 g Pd − 1 s − 1 ), due to the covered Ce1−xPdxO2−δ surface by surface PdOx species.

The adsorption and desorption of CO2 on MgO/Al2O3 were investigated by in situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS) combined with the method of curve-fitting analysis. The spectroscopic results indicate that there are three chemisorbed surface species formed on the MgO/Al2O3, i.e., free carbonate ion, bridged carbonate, and bidentate carbonate species, which correspond to the peaks at 1675, 1403, and two peaks at 1610 and 1340 cm−1, respectively, when the sample was exposed in CO2 flow at 130 °C. The quantification analysis of the spectra during CO2 adsorption and desorption shows that the formation and desorption rates of all surface species are coverage dependent. Among the three species, the bridged carbonate shows the highest speed of formation and desorption, indicating that this type of species may be beneficial to CO2 capture and release. It should also be noted that the contribution of support Al2O3 to CO2 capture is negligible. This study may help us to understand the interaction between CO2 and metal oxides and thus to give more insights into CO2 capture using solid sorbents.

The PdO/Ce1–xPdxO2−δ catalyst prepared by a solution-combustion method contained free surface PdO species and PdO species in Ce1–xPdxO2−δ solid solution, whereas the PdO/CeO2 catalyst prepared by an impregnation method contained only free surface PdO species. The free surface PdO species could be removed by nitric acid. Contributions of the PdO species to catalytic CO oxidation were quantitatively evaluated. The free surface PdO species in the PdO/Ce1–xPdxO2−δ catalyst had the highest activity (969.3 μmolCO gPd–1 s–1), those in the PdO/CeO2 catalyst had medium activity (109.0 μmolCO gPd–1 s–1), and the PdO species in the Ce1–xPdxO2−δ solid solution had the lowest activity (13.2 μmolCO gPd–1 s–1). Synergetic effects of PdO species were responsible for the enhanced reactivity of the PdO/Ce1–xPdxO2−δ catalyst, as the free surface PdO species provided CO chemisorption sites and the Ce1–xPdxO2−δ solid solution generated more oxygen vacancies for oxygen activation.

A series of CuO/CeO2 and inverse CeO2/CuO catalysts were prepared by an incipient wetness impregnation method and tested for CO oxidation. Crystallite sizes of CeO2 and CuO were evaluated by X-ray diffraction and N2O chemisorption, as well as transmission electron microscopy. It was found that a CuO(5)/CeO2-500 catalyst with a CuO crystallite size of 4.1 nm and a CeO2(5)/CuO-500 catalyst with a CeO2 crystallite size of 4.0 nm had identical activities, indicating that the reaction may occur at the interface of CuO−CeO2. According to the turnover frequency based on CuO sites located on the CuO−CeO2 interface, the activity on the larger CuO crystallite was much higher than that on the smaller one, indicating that CuO−CeO2 catalyst for CO oxidation is structure-sensitive. The enhanced activity was ascribed to a higher density of chemisorbed CO on the active sites for the larger CuO crystallite.

Ce0.9Pr0.1O2-δ, Ce0.95Cu0.05O2-δ, and Ce0.9Pr0.05Cu0.05O2-δ mixed oxides and pure CeO2 were prepared with a sol−gel method and were characterized by XRD, in situ Raman, and in situ DRIFTS techniques. The XRD results confirmed the formation of Ce−Pr−O solid solution. The Raman results indicated that a higher concentration of oxygen vacancies was obtained on the Pr-doped samples compared to the Ce0.95Cu0.05O2-δ and pure CeO2 samples. Surface chemical states of the Ce0.9Pr0.1O2-δ and Ce0.9Pr0.05Cu0.05O2-δ mixed oxides were determined by in situ Raman spectroscopy, which indicated that the surfaces of the two mixed oxides were both close to oxidation state during the reaction, despite of the presence of reducing reactant CO in the gas mixture. The in situ DRIFTS results evidenced the chemisorption of CO in the Cu-containing samples. The catalysts were tested for CO oxidation, and it was found that the enhanced reactivity was closely related to the higher concentrations of the oxygen vacancies and the chemisor...