B.S. Liu

Sol–Gel-Generated La2NiO4 for CH4/CO2 Reforming

A stable La2NiO4 catalyst active in CH4/CO2 reforming has been prepared by a sol–gel method. The catalyst was characterized by techniques such as XRD, BET, TPR and TG/DTG. The results show that the conversions of CH4 and CO2 in CH4/CO2 reforming over this catalyst are significantly higher than those over a Ni/La2O3 catalyst prepared by wet impregnation and those over a La2NiO4/γ-Al2O3 catalyst. The TG/DTG outcome confirmed that the amount of carbon deposition observed in the former case was less than that observed in the latter two cases, a phenomenon attributable to the uniform dispersion of nanoscale Ni particles in the sol–gel-generated La2NiO4 catalyst.

Preparation and characterization of NiP amorphous alloy/ceramic composite membrane

Abstract The NiP amorphous alloy/ceramic composite membrane of high selectivity and permeability for hydrogen was prepared by a new technique of partial electroless plating. Its permeability and ideal separation factor for H2/Ar were investigated. The results demonstrated that the permeability of the NiP amorphous alloy membrane was almost the same as that of a porous inorganic membrane, but the separation factor for H2/Ar through the NiP membrane was obviously higher than that through a porous inorganic one. The morphology and microstructure of NiP amorphous alloy/ceramic composite membrane were characterized by SEM and XRD.

A La2NiO4-Zeolite Membrane Reactor for the CO2 Reforming of Methane to Syngas

The La2NiO4-zeolite membrane was prepared by means of in situ hydrothermal synthesis. Techniques such as XRD, SEM-EDX, and BET were used to acquire information as related to the structure, morphology and the pore size distribution of the membrane. At room temperature, we observed a H2/CH4 separation factor of 9.2, considerably higher than the Knudsen diffusion value. With the simultaneous separation of CO and H2 in the membrane reactor, both CO2 and CH4 conversions were enhanced in the CH4/CO2 reforming reaction.

Amorphous alloy/ceramic composite membrane: preparation, characterization and reaction studies

A Ni-P amorphous alloy/ceramic membrane with high selectivity and permeability for hydrogen was prepared by a novel technique of local electroless Ni-plating with metal-activated paste. The separation factor obtained is higher for H2/Ar compared with γ-Al2O3/ceramic composite membrane. In addition, two kinds of Ni-P alloy/ceramic composite membranes, as-prepared and crystallized ones, were applied to the membrane reactor of ethanol dehydrogenation, and the effect of the reaction temperature, argon sweeping rate and space time on ethanol conversion and yield of acetaldehyde was investigated. The results demonstrated that ethanol conversion in an as-prepared Ni-P amorphous alloy membrane reactor was significantly higher than that in a Ni-P alloy membrane reactor after crystallization, owing to an original structure of as-prepared Ni-P membrane. Meanwhile, the morphology of the membrane was observed by SEM. The crystallized process of non-supported Ni-P alloy membrane was detected by XRD. The surface composition and valence state of the membrane before and after reaction was investigated by XPS.

Formation of polycyclic aromatic hydrocarbons from acetylene over nanosized olivine-type silicates

The formation mechanism of polycyclic aromatic hydrocarbon (PAH) molecules in interstellar and circumstellar environments is not well understood although the presence of these molecules is widely accepted. In this paper, addition and aromatization reactions of acetylene over astrophysically relevant nesosilicate particles are reported. Gas-phase PAHs produced from exposure of acetylene gas to crystalline silicates using pulsed supersonic jet expansion (SJE) conditions were detected by time-of-flight mass spectrometry (TOF-MS). The PAHs produced were further confirmed in a separate experiment using a continuous flow fixed-bed reactor in which acetylene was introduced at atmospheric pressure. The gas-phase effluent and solutions of the carbonaceous compounds deposited on the nesosilicate particles were analyzed using gas chromatography-mass spectrometry (GC-MS). A mechanism for PAH formation is proposed in which the Mg(2+) ions in the nesosilicate particles act as Lewis acid sites for the acetylene reactions. Our studies indicate that the formation of PAHs in mixed-chemistry astrophysical environments could arise from acetylene interacting with olivine nano-particles. These nesosilicate particles are capable of providing catalytic centres for adsorption and activation of acetylene molecules that are present in the circumstellar environments of mass-losing carbon stars. The structure and physical properties of the particles were characterized by means of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and high-resolution transmission electron microscopy (HRTEM) techniques.

Catalytic Dehydrogenation of Ethanol in Ru-Modified Alumina Membrane Reactor

Abstract Ru-modified alumina composite membranes were prepared by the sol-gel method. The pore size distribution from nitrogen adsorption showed that average pore diameters were 3.1–4.5 nm, and the ideal separation factor was obviously higher than that of a pure γ-AI2O3 membrane. Ethanol dehydrogenation was carried out in the Ru-modified alumina membrane reactors. The effects of the reaction temperature, feed rate, and argon sweep flow rate on acetaldehyde yield were investigated. The results showed that the yield of acetaldehyde increased by 25–28% at the same conditions in a Ru-modified alumina membrane reactor. The reduced temperature of the Ru-modified alumina composite membrane was measured by temperature-programmed reduction, and the morphology of the membrane was characterized by SEM, TEM, and XRD.

Catalytic dehydrogenation of ethanol in PdM/γ-Al2O3 composite membrane reactors

Abstract Alumina membranes modified by Pd M (M Ru, Rh, Ni, Ag) and Pd were prepared by the solgel method, and characterized by SEM, XRD and N 2 adsorption. The single or binary metals were highly dispersed in alumina. The average pore diameters of binary metals modified membranes were 4–7 nm, which was a bit smaller than that for Pd single metal modified alumina membrane. The H 2 /N 2 gas separation tests showed that the separation factor of the gaseous mixture exceeded the Knudsen value (3.74). The dehydrogenation of ethanol to acetaldehyde was carried out in membrane reactors incorporating Pd M and Pd modification. The yield of acetaldehyde in Pd Ru, Pd Ag, Pd Rh modified membrane reactors was higher than that in single metal Pd modified membrane reactor, while the yield in the Pd Ni/γ-Al 2 O 3 membrane reactor was lower than that in Pd/γ-Al 2 O 3 membrane reactor. At moderate reaction conditions, the yield increased by 15% in Pd Ru modified membrane reactor compared with the thermodynamic equilibrium value. The properties and characteristics of all modified membranes were compared and discussed in this paper.

A novel NiP–Cu composite membrane reactor for catalytic dehydrogenation of ethanol

Abstract A NiP–Cu multi-layer composite membrane was prepared by an improved technique of electroless plating with metal-activation paste and applied to membrane reactor of ethanol dehydrogenation. The results showed that the yields of acetaldehyde observed over a NiP–Cu composite membrane reactor were obviously higher than those observed over a Ni–P membrane reactor due to catalytic activity of NiP–Cu membrane itself. Meanwhile the effect of the reaction temperature, sweeping argon rate and space time, W / F , on the ethanol conversion and the selectivity of acetaldehyde are investigated, and the mechanism of catalytic dehydrogenation for ethanol going through NiP–Cu composite membrane was analyzed. The surface morphology and bulk structure of NiP–Cu composite membrane were characterized by means of technique such as SEM and XRD.

Catalytic conversion of acetylene to polycyclic aromatic hydrocarbons over particles of pyroxene and alumina.

Polycyclic aromatic hydrocarbons (PAHs) are known to be present in many astrophysical objects and environments, but our understanding of their formation mechanism(s) is far from satisfactory. In this paper, we describe an investigation of the catalytic conversion reaction of acetylene gas to PAHs over pyroxene and alumina. Crystalline silicates such as pyroxenes (with general formula [Mg, Fe]SiO3) and alumina (Al2O3) are observed astrophysically through their infrared spectra and are likely to promote grain surface chemical reactions. In the experiments reported here, gas-phase PAHs were produced by the catalytic reaction of acetylene over crystalline silicates and alumina using a pulsed jet expansion technique and the gaseous products detected using time-of-flight mass spectrometry. In a separate experiment, the catalytic formation of PAHs from acetylene was further confirmed with acetylene gas at atmospheric pressure flowing continuously through a fixed-bed reactor. The gas effluent and carbonaceous compounds deposited on the catalysts were dissolved separately in dichloromethane and analysed using gas chromatography–mass spectrometry. Among the samples studied, alumina showed higher activity than the pyroxene-type grains for the acetylene reaction. It is proposed that formation of the PAHs relies on the Mg2+ ions in the pyroxenes and Al3+ ions in alumina, where these ions act as Lewis acid sites. X-ray diffraction, Fourier transform infrared and high-resolution transmission electron microscopy techniques were used to characterize the structure and physical properties of the pyroxene and alumina samples.

Catalytic conversion of acetylene to polycyclic aromatic hydrocarbons (PAHs) particles of olivine, pyroxene, and forsterite-type silicates and silicon carbide

This journal vol. entitled: Astrochemistry of Dust, Ice and Gas, Leiden University, The Netherlands, 7-9 April 2014