Xiaoyu Niu

Selective Hydrogenation of Cinnamaldehyde to Cinnamal Alcohol over Platinum/Graphene Catalysts

Catalysts made of Pt nanoparticles dispersed on graphene (X wt %Pt/G, X=2.0, 3.5, and 5.0) were prepared and characterized by XRD, Raman spectroscopy, BET surface area measurements, TEM, and X‐ray photoelectron spectroscopy (XPS), and a 3.5 wt % Pt supported on Vulcan Carbon catalyst (3.5 wt %Pt/VC) was included as a reference. Although the mean Pt nanoparticle size is approximately 4.4 nm for all X wt %Pt/G and 3.5 wt %Pt/VC catalysts, cinnamal alcohol was produced with high selectivity only with the graphene‐supported catalysts: 92 % conversion and 88 % selectivity toward cinnamal alcohol were obtained with 3.5 wt %Pt/G. This catalyst also showed good stability in recycling tests. The good selectivity observed with the graphene‐based catalysts is attributed to the higher fraction of reduced surface Pt0 atoms seen on the surface of the Pt nanoparticles (determined by XPS). This interpretation is consistent with DFT calculations. Additional π–π interactions between cinnamaldehyde and graphene may also play a role in the selective hydrogenation of cinnamaldehyde.

Preparation of Hollow CuO@SiO2 Spheres and Its Catalytic Performances for the NO + CO and CO Oxidation

The hollow CuO@SiO2 spheres with a mean diameter of 240 nm and a thin shell layer of about 30 nm in thickness was synthesized using an inorganic SiO2 shell coating on the surface of Cu@C composite that was prepared by a two-step hydrothermal method. The obtained hollow CuO@SiO2 spheres were characterized by ICP-AES, nitrogen adsorption-desorption, SEM, TEM, XRD, H2-TPR, CO-TPR, CO-TPD and NO-TPD. The results revealed that the hollow CuO@SiO2 spheres consist of CuO uniformly inserted into SiO2 layer. The CuO@SiO2 sample exhibits particular catalytic activities for CO oxidation and NO + CO reactions compared with CuO supported on SiO2 (CuO/SiO2). The higher catalytic activity is attributed to the special hollow shell structure that possesses much more highly dispersed CuO nanocluster that can be easy toward the CO and NO adsorption and the oxidation of CO on its surface.

Effect of Ni doping in NixMn1−xTi10 (x = 0.1–0.5) on activity and SO2 resistance for NH3-SCR of NO studied with in situ DRIFTS

In this work, a series of NixMn1−xTi10 (x = 0.0–0.5) catalysts were synthesized using a one-pot sol–gel method for selective catalytic reduction (SCR) of NO with NH3. The effects of Ni doping on the catalytic activity and SO2 resistance were investigated by XRD, TEM-EDS, XPS, NH3-TPD, H2-TPR, SO2-TPD and in situ DRIFTS. It is found that the higher the amounts of surface Mn4+ and Oα species existing on the catalyst surface, the greater the oxidation ability that they present for NO and NH3, which results in better activity at low temperature and worse selectivity to N2 at high temperature due to the overoxidation of NH3. Among NixMn1−xTi10 (x = 0.0–0.5), the Ni0.4Mn0.6Ti10 catalyst exhibited excellent NH3-SCR activity, a wide temperature window (190–360 °C) and good H2O and SO2 durability even in the presence of 100 ppm SO2 and 15% H2O under a GHSV of 40 000 h−1, which is very competitive for the practical application in controlling the NOx emission from stationary sources. It is concluded that more surface Lewis acid sites and the appropriate contents of surface active Mn4+ and surface oxygen species on the surface of Ni0.4Mn0.6Ti10 play key roles in the special SCR performance due to the interactions among Mn, Ni and Ti oxides. The SO2-TPD and in situ DRIFTS results confirm the reason for the good SO2 resistance of the Ni0.4Mn0.6Ti10 catalyst. Moreover, in situ DRIFTS results reveal that the NH3-SCR reaction over Ni0.4Mn0.6Ti10 mainly follows the Eley–Rideal (E–R)-type mechanism.

Preparation of KF–La2O2CO3 solid base catalysts and their excellent catalytic activities for transesterification of tributyrin with methanol

A series of 25% KF–La2O2CO3 catalysts (25-KF–LOC-x, x = 673, 723 and 773) were prepared at different calcination temperatures, which were tested as basic catalysts for the transesterification of tributyrin with methanol to produce methyl butyrate and characterized by means of XRD, SEM, CO2-TPD, FTIR, XPS and XRF. It was found that the calcination temperature greatly influences the catalytic activity, and its order is 25-KF–LOC-673 < 25-KF–LOC-723 < 25-KF–LOC-773. Especially, the 25-KF–LOC-773 catalyst exhibits a very high activity, and the conversion of tributyrin is nearly 100%, the yield of methyl butyrate reaches 94% at 308 K. The activation energy of the 25-KF–LOC-773 catalyst is as low as 55.03 kJ mol−1. The excellent catalytic activity of the 25-KF–LOC-773 catalyst can be attributed to the largest amount of surface hydroxyl among these 25-KF–LOC-x catalysts. The results indicate that the Bronsted base is the main active site at low reaction temperature. The recycling use and stability have been investigated over the 25-KF–LOC-773 catalyst. The results indicate that the 25-KF–LOC-773 catalyst has a high stability after being stored for 90 days. The deactivation of the used 25-KF–LOC-773 catalyst at 308 K is due to the loss of hydroxyl on the surface. However, the conversion of tributyrin can reach 91%, and the yield of methyl butyrate also can achieve 64% when the transesterification reaction is performed at 338 K over the second used 25-KF–LOC-773 catalyst. It indicates that the second used 25-KF–LOC-773 catalyst still possesses good catalytic activity at the higher reaction temperature due to the unchanged strong Lewis basic sites provided with surface oxygen anions.

Soot Combustion over Nanostructured Ceria with Different Morphologies

In this study, nano-structure ceria with three different morphologies (nanorod, nanoparticle and flake) have been prepared by hydrothermal and solvothermal methods. The ceria samples were deeply characterized by XRD, SEM, TEM, H2-TPR, XPS and in-situ DRIFTS, and tested for soot combustion in absence/presence NO atmospheres under loose and tight contact conditions. The prepared ceria samples exhibit excellent catalytic activities, especially, the CeO2 with nanorod (Ce-R) shows the best catalytic activity, for which the peak temperature of soot combustion (Tm) is about 500 and 368 °C in loose and tight contact conditions, respectively. The catalytic activity for Ce-R is higher than that of the reported CeO2 catalysts and reaches a level that of precious metals. The characterization results reveal that the maximal amounts of adsorbed oxygen species on the surface of the nanostructure Ce-R catalyst should be the crucial role to decide the catalytic soot performance. High BET surface area may also be a positive effect on soot oxidation activity under loose contact conditions.

Catalytic Decomposition of N2O over Co–Ti Oxide Catalysts: Interaction between Co and Ti Oxide

A series of CoxTi catalysts with different Co/Ti molar ratios (x=0.2, 0.4, 0.6, and 0.8) were prepared by the sol‐gel method and used for N2O decomposition. The catalysts were characterized by XRD, X‐ray photoelectron spectroscopy (XPS), TEM, temperature‐programmed reduction with H2, temperature‐programmed desorption of O2, diffuse reflectance UV/Vis, Raman spectra, and N2 adsorption–desorption measurements. The results indicate that the CoxTi catalysts possess high Brunauer–Emmett–Teller (BET) surface area, more surface Co3+, and even better structural stability than Co3O4 as a result of the strong interactions between Co and Ti oxide. Deactivation occurred over time for the Co3O4 catalyst, however, Co0.6Ti maintains nearly 100 % N2O conversion for at least 30 h. Moreover, the Co0.6Ti catalyst showed much stronger resistance against 1.5 vol. % O2, 2.4 vol. % H2O, or 1.6 vol. % NO in the feed compared with the Co3O4 catalyst. The excellent activity of the Co0.6Ti catalyst can be attributed to the higher amount of surface Co3+ derived from the interaction of the Co and Ti oxide in the CoxTi catalysts.

Effect of carbon nanosheets with different graphitization degrees as a support of noble metals on selective hydrogenation of cinnamaldehyde

In this work, Pt and Pd catalysts supported on carbon nanosheets (CNS) with different graphitization degrees were prepared via a simple borohydride reduction method. The effect of graphitization degree on the catalytic activity of Pt/CNS and Pd/CNS was investigated to obtain the optimal activity. The prepared catalysts were well characterized by X-ray diffraction (XRD), Raman, transmission electron microscopy (TEM) and X-ray photoemission spectroscopy (XPS). The activity and selectivity of Pt/CNS and Pd/CNS catalysts increases with the rise of the graphitization degree of CNS. A high graphitization degree of the CNS support can enhance the transfer of electrons from the CNS support to Pt and Pd nanoparticles, leading to the increase in the surface Pt0 and Pd0 content. The more surface Pt0 and Pd0 content the catalyst has, the higher selectivity to COL and CALD it exhibits, respectively. The good graphitization degree of the CNS support is an advantage of the strong π–π interactions between CAL and the surface sp2-bonded of CNS support. Thus, the different catalytic activity and selectivity over the Pt/CNS and Pd/CNS catalysts are attributed to the surface Pt0 and Pd0 content and the adsorption capacity for CAL on the catalyst surface that are closely related to the graphitization degree of CNS.

Effect of cerous phosphates with different crystal structures on their acidity and catalytic activity for the dehydration of glucose into 5-(hydroxymethyl)furfural

A series of cerous phosphate (CP) catalysts with different crystal structures were synthesized by a hydrothermal method at different temperatures (120, 140, 160, 180 and 200 °C) and their performances for the dehydration of glucose into 5-(hydroxymethyl)furfural (HMF) were also thoroughly investigated. These catalysts were characterized by XRD, N2 adsorption–desorption, SEM, in situ DRIFT, NH3-TPD and XPS. The results indicate that changing the temperature of synthesis will lead to a transformation of the crystal phase and morphology from 120 °C (nanoparticles, hexagonal structure) to 200 °C (nanorods, monoclinic structure); also, the different crystal phases possess different surface Ce4+ amounts and acidities. A good linear correlation is found between the Lewis acid content and the surface Ce4+ amount among these CP catalysts, and very good linearity is also displayed between the Lewis acid amount and the conversion of glucose or the selectivity of HMF, which indicates that Lewis acidity plays an important role in the dehydration of glucose to HMF. CP120, which has a hexagonal crystal structure, exhibits the best catalytic activity (97% conversion of glucose and 61% yield of HMF) because it has the highest amounts of Lewis acid and total acid.

Preparation of Pd supported on La(Sr)-Mn-O Perovskite by microwave Irradiation Method and Its Catalytic Performances for the Methane Combustion

In this work, a series of palladium supported on the La0.8Sr0.2MnO3.15 perovskite catalysts (Pd/LSM-x) with different Pd loading were prepared by microwave irradiation processing plus incipient wetness impregnation method and characterized by XRD, TEM, H2-TPR and XPS. These catalysts were evaluated on the lean CH4 combustion. The results show that the Pd/LSM-x samples prepared by microwave irradiation processing possess relative higher surface areas than LSM catalyst. The addition of Pd to the LSM leads to the increase in the oxygen vacancy content and the enhancement in the mobility of lattice oxygen which play an important role on the methane combustion. The Pd/LSM-3 catalysts with 4.2wt% Pd loading exhibited the best performance for CH4 combustion that temperature for 10% and 90% of CH4 conversion is 315 and 520 °C.

Activity and deactivation of Ru supported on La1.6Sr0.4NiO4 perovskite-like catalysts prepared by different methods for decomposition of N2O

In this paper, the activity and stability of Ru supported on La1.6Sr0.4NiO4 perovskite-like catalysts prepared by two different methods, incipient wetness procedures with the addition of ethylene glycol (Ru/LSN-EG) and without ethylene glycol (Ru/LSN), were investigated for the decomposition of N2O. The catalysts were fully characterized by means of XRD, elemental analysis, N2-physisorption, TEM, H2-TPR, N2O-TPD and XPS. The Ru/LSN-EG catalyst retained high activity for 10 h without deactivation, which is attributed to the stable Ru3+ species, the much higher mobility of lattice oxygen and the regeneration ability of oxygen vacancies. However, the Ru/LSN catalyst presented deactivation; the initial N2O conversion of about 95% was only maintained for the first hour and decreased with time to 55% after 6 h. The reasons for this deactivation were investigated by a series of experiments and characterizations. The results indicate that the deactivation of the Ru/LSN catalyst can be ascribed to the difficult desorption of the oxygen species derived from N2O decomposition on the active sites; moreover, all the metallic Ru and Ru3+ species are oxidized to high oxidation state Ru4+ species. All the results demonstrated that the Ru3+ species was more favorable for N2O decomposition. Furthermore, the effects of O2 and H2O on the decomposition of N2O were also evaluated over the Ru/LSN-EG catalyst. High stability and no irreversible deactivation of the Ru/LSN-EG catalyst, even in the presence of O2 and H2O, were found.