Jun Ren

Ni/SBA-15 catalysts for CO methanation: effects of V, Ce, and Zr promoters

Ni/SBA-15 catalysts with various promoters (V, Ce, and Zr) were prepared by an ultrasonic coimpregnation method and used in CO methanation. The addition of promoters played a significant role in improving the catalytic activity of the Ni/SBA-15 catalyst. This improvement could be explained by changes in the valences of the V and Ce promoter species through an oxidation–reduction shift cycle process (Mx+ ↔ My+, M = V, Ce), which could trigger electron transfer. This transfer enhanced the electron density of active Ni species and promoted CO dissociation. The Zr promoter could produce oxygen vacancies during calcination and reduction, thereby increasing the ability of CO to adsorb and dissociate. In addition, the formation of a Si–O–M bond (M = Zr, Ce, V) increased the interaction between the active species and support, which facilitated CO methanation. Under 1.0 MPa and a WHSV of 15u2006000 mL g−1 h−1, 10Ni–5V/SBA-15 exhibited the best catalytic performance (99.9% CO conversion; 95.5% CH4 selectivity).

Influence of Microwave Irradiation on the Structural Properties of Carbon‐Supported Hollow Copper Nanoparticles and Their Effect on the Synthesis of Dimethyl Carbonate

Novel activated carbon (AC)‐supported highly dispersed hollow Cu nanoparticles (NPs) (Cu/AC) with exposed {1u20091u20091} facets have been prepared by microwave irradiation for the synthesis of dimethyl carbonate (DMC). In particular, Cu NPs with a large cavity diameter of 35u2005nm are formed after irradiation from room temperature to 360u2009°C within a mere 8u2005min without additional irradiation, thus benefiting from the rapid heating of the microwave procedure. In this study, an Ostwald ripening mechanism is proposed. DFT calculations are consistent with the analysis of CO temperature‐programmed desorption, which found that Cu(1u20091u20091) facets are more favorable for the weak adsorption of CO, which supports the formation of DMC. The as‐prepared catalysts exhibit the highest DMC formation rate in terms of turnover frequency and 100u2009% selectivity for DMC can be achieved. The large surface area of the hollow Cu NPs and the exposed {1u20091u20091} crystal planes are highlighted as being responsible for the excellent catalytic rate and superior selectivity, respectively.

Mechanism of microwave-induced carbothermic reduction and catalytic performance of Cu/activated carbon catalysts in the oxidative carbonylation of methanol

Activated carbon–supported copper catalysts (Cu/AC) were prepared by impregnation of AC support with aqueous copper (II) nitrate solutions and subsequent microwave carbothermic reduction under different irradiation conditions. This was done to investigate the effect of the valence of copper on the vapor-phase oxidative carbonylation of methanol to dimethyl carbonate (DMC). Thermogravimetric analysis–mass spectrometry were carried out to explore the mechanism of carbothermic reduction in catalyst preparation. X-ray diffractometry, hydrogen temperature-programmed reduction, X-ray photoelectron spectroscopy, and scanning electron microscopy were employed to examine the bulk and surface properties of the Cu/AC catalysts. Microwave irradiation of the catalyst precursors rapidly induced a series of successive reactions, namely decomposition of Cu2(OH)3NO3 into CuO, reduction in CuO to Cu2O, and carbothermic reduction in Cu2O to Cu0. These reactions resulted in mixed-valence copper species, CuO, Cu2O, and Cu0, in the Cu/AC catalysts. CuO, Cu2O, and Cu0 were active in DMC synthesis, but the catalytic performance of Cu/AC was highly dependent on the Cu0 concentration. High irradiation temperatures resulted in higher Cu0 concentrations because of enhanced carbothermic reduction, and fast heating rates improved the degree of dispersion of Cu2O and Cu0. The catalyst irradiated at 540xa0°C at a heating rate of 48xa0°Cxa0min−1 showed the highest catalytic activity in the oxidative carbonylation of methanol.

The growth of Nin clusters and their interaction with cubic, monoclinic, and tetragonal ZrO2 surfaces–a theoretical and experimental study

Ni/ZrO2 catalysts are widely used in many reactions such as CO/CO2 methanation and reforming of acetic acid. The kind of ZrO2 phase plays a vital role in the catalytic properties of Ni/ZrO2 catalysts that depend on the interface between zirconia and supported Ni particles. Periodic density functional theory was applied to systematically investigate the interaction of a single Ni atom and Nin (n = 2–4) clusters with cubic ZrO2 (c-ZrO2) (111), monoclinic ZrO2 (m-ZrO2) (−111), and tetragonal ZrO2 (t-ZrO2) (101) surfaces. Adsorption of the Ni atom and all Nin (n = 2–4) clusters on zirconium dioxide surfaces was kinetically and thermodynamically preferred. Adsorption of Nin clusters on the m-ZrO2(−111) surface is more stable than that on the t-ZrO2(101) surface, and the t-ZrO2(101) surface is more stable than the c-ZrO2(111) surface. The aggregation ability of Nin clusters on different ZrO2 surfaces and the isolated clusters follow the trend m-ZrO2(−111) < t-ZrO2(101) < c-ZrO2(111) < isolated cluster. Therefore, Nin clusters can have a better dispersion and can inhibit aggregation due to the support. What is more, the single-phase ZrO2 was synthesized and loaded with an equivalent content of active Ni components. The experimental results obtained by X-ray photoelectron spectroscopy analysis support the hypothesis that has been deduced.

Study on the formation and role of copper chloride hydroxide in the oxidative carbonylation of methanol to dimethyl carbonate

The synthesis of dimethyl carbonate by oxidative carbonylation of methanol over CuCl/SiO2-TiO2 catalysts has been investigated in a slurry reaction system. The γ-Cu2(OH)3Cl crystals were detected by X-ray diffraction on the catalysts after reaction. It was revealed that γ-Cu2(OH)3Cl was formed by CuCl reacting with O2 and by-product water. The catalytic tests showed that γ-Cu2(OH)3Cl was largely inactive for this reaction, may be attributed to its high stability that resisted the Cu+/Cu2+ redox cycle.

Influence of oxygen-containing groups of activated carbon aerogels on copper/activated carbon aerogels catalyst and synthesis of dimethyl carbonate

Active catalysts that were prepared by dispersing copper (Cu) nanoparticles on potassium hydroxide (KOH)-activated carbon aerogels (ACAs) were investigated in the synthesis of dimethyl carbonate (DMC) by vapor-phase oxidative carbonylation of methanol. The effect of mesopores and surface oxygen-containing groups (OCGs) including Cxa0=xa0O, COOH and OH of the ACAs on the dispersion of active species and catalytic properties was determined. An increase in molar ratio of resorcinol to anhydrous sodium carbonate (R/C) lead to the creation of mesopores within the original carbon aerogels (CAs), which benefits to molecules mass transport. The amount of surface OCGs increased positively with KOH/CAs mass ratio, which affected the valence distribution of Cu species, improved the Cu dispersion and enhanced the catalytic activity. For an optimum R/C of 500 and a KOH/CAs mass ratio of 4, the Cu/ACAs catalyst maintains a prominent DMC space time yield of 338.7xa0mg/(gxa0h) and a methanol conversion of 2.5%. Density functional theory calculations indicate that of the different surface OCGs of the carbon support, enrichment in Cxa0=xa0O group enhances the interaction between the metal and the ACAs support significantly and contributes to the formation of the smallest Cu nanoparticles and the highest catalytic activity.

Fabrication of Yolk-Shell Cu@C Nanocomposites as High-Performance Catalysts in Oxidative Carbonylation of Methanol to Dimethyl Carbonate

A facile way was developed to fabricate yolk-shell composites with tunable Cu cores encapsulated within hollow carbon spheres (Cu@C) with an average diameter about 210xa0nm and cavity size about 80xa0nm. During pyrolysis, the confined nanospace of hollow cavity ensures that the nucleation-and-growth process of Cu nanocrystals take place exclusively inside the cavities. The size of Cu cores can be easily tuned from 30 to 55xa0nm by varying the copper salt concentration. By deliberately creating shell porosity through KOH chemical activation, at an optimized KOH/HCS mass ratio of 1/4, the catalytic performance for the oxidative carbonylation of methanol to dimethyl carbonate (DMC) of the activated sample is enhanced remarkably with TOF up to 8.6xa0h−1 at methanol conversion of 17.1%. The activated yolk-shell catalyst shows promising catalytic properties involving the reusability with slight loss of catalytic activity and negligible leaching of activated components even after seven recycles, which is beneficial to the implementation of clean production for the eco-friendly chemical DMC thoroughly.

Using data mining technology in screening potential additives to Ni/Al2O3 catalysts for methanation

In order to improve the catalytic activity, the screening of optimal potential additives to Ni/Al2O3 catalysts for CO methanation was performed by data mining techniques with a combination of principal component analysis, K-means algorithm and Gaussian process regression (GPR). Based on a tremendous amount of data from previous studies, 63 elements excluding gaseous, poisonous and radioactive ones were selected as initial candidates. After the screening by element clustering, the activities of Ni/Al2O3 catalysts promoted by 9 representative elements including Na, Ca, Cr, B, La, Ru, Cu, Zn, and In were measured, and the catalytic activity was analyzed in terms of T50, which represents the temperature at a CO conversion rate of 50%. The activities and physicochemical properties of the nine elements were used to construct regression models by GPR. The regression models predicted that as a potential additive, Re promotes the activity; we experimentally verified that the T50 dropped by 78 °C relative to that of the unmodified Ni/Al2O3 catalyst. It can be considered to be the most effective one of all additives. The advantages of using data mining techniques in catalyst research are that they reduce the number of catalysts to be empirically analyzed and they accelerate the discovery of new catalysts.

Surface Properties and Reactivity of Iron-Doped Titanium Oxides Catalysts in Oxidative Dehydrogenation of Ethylbenzene with CO2

Abstract The effect of Fe3+ doping level on the surface properties and catalytic performance of a series of iron-doped titanium oxide catalysts (1–7 mol% Fe3+) prepared using an acid-catalyzed sol-gel method was investigated in oxidative dehydrogenation of ethylbenzene with CO2. The characterization of catalysts was carried out by means of x-ray powder diffraction (XRD), temperature programmed reduction (TPR), and the method of Brunauer, Emmett, and Teller (BET). It was found that the capacity of isolated Fe3+ centers in titania matrix is responsible for the catalytic performance; the catalysts exhibit the best activity at the loading level of Fe3+, about 3 mol%. In addition, it was shown that the appropriate pore size of the catalysts ranges from 5 nm to 25 nm; the selectivity to styrene increases with an increase in the specific surface area of the appropriate pores.