Shishan Sheng

Partial oxidation of methane to syngas over nickel-based catalysts modified by alkali metal oxide and rare earth metal oxide

Abstract The NiO/Al2O3 catalyst was modified by alkali metal oxide (Li, Na, K) and rare-earth metal oxide (La, Ce, Y, Sm) in order to improve the thermal stability and the carbon-deposition resistance during the partial oxidation of methane to syngas (POM) reaction at high temperature. The reaction performance, thermal stability, structure, dispersity of nickel and carbon-deposition of the modified NiO/Al2O3 catalyst and unmodified NiO/Al2O3 catalyst were investigated by a series of characterization techniques including flow-reaction, BET, XRD, CO chemisorption and TG analysis. The results indicated that the modification with alkali metal oxide and rare-earth metal oxide improves the dispersion of active component nickel and the activity for the POM reaction over the nickel-based catalysts, and enhances their thermal stability during high temperature reaction and the ability to suppress the carbon-deposition over the nickel-based catalysts during the POM reaction. The nickel-based catalysts modified by alkali metal oxide and rare-earth metal oxide have excellent POM reaction performance (CH4 conversion of 94.8%, CO selectivity of 98.1%, 2.7×104l/kg·h), excellent stability and carbon-deposition resistance.

Investigation on POM reaction in a new perovskite membrane reactor

A perovskite-type oxide of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCFO) shows mixed (electronic/oxygen ionic) conductivity at high temperatures. Membrane made of the oxide has high oxygen permeability under air/helium oxygen partial pressure gradient. At 850 ◦ C, oxygen permeation rate maintained about 1.15 ml/cm 2 min for more than 1000 h under ambient air/helium oxygen gradient. A membrane reactor constructed from the oxide membrane was applied for the partial oxidation of methane (POM) to syngas, LiLaNiOx/-Al2O3 with 10 wt.% Ni loading was used as the packed catalyst. At the initial stage, oxygen permeation rate, methane conversion and CO selectivity were closely related with the state of the catalyst. Less than 21 h was needed for the oxygen permeation rate to reach its steady state. A membrane reactor made of BSCFO was successfully operated for POM reaction at 875 ◦ C for about 500 h without failure, with methane conversion of >97%, CO selectivity of >95% and oxygen permeation rate of about 11.5 ml/cm 2 min. Under membrane reaction condition, the POM reaction mechanism was suggested to obey the CRR (complete combustion of CH4 to CO2 and H2O and a subsequent reforming reaction of the residual CH4 and with CO2 and H2 Ot o CO and H 2) mechanism.

Pd/ceramic hollow fibers for H2 separation

Highest ratio of separation area to volume of membranes can be achieved by the use of hollow fiber configuration. Ceramic hollow fibers with outer diameters no larger than 1 mm are used as supports for dense Pd membranes. Pd layers of 2/3 mm thick are deposited by electroless plating technique. H2 permeances are 7/10 m 3 /m 2 h bar at 350/ 450 8C. The durability in H2 is tested at 430 8C for 800 h. H2 permeance keeps over 10 m 3 /m 2 h bar and the separation factor of H2/N2 over 1000, which shows the possibilities to be applied in H2 separation and catalysis at high temperatures.

Thin dense Pd membranes supported on α-Al2O3 hollow fibers

Macroporous α-Al2O3 hollow fibers are used as supports for thin dense Pd membranes; these membranes show a high and stable H2 flux in permeance studies.

Partial oxidation of methane and ethane to synthesis gas over a LiLaNiO/γ-Al2O3 catalyst

Partial oxidation of methane and ethane to synthesis gas over a LiLaNiO/g-Al2O3 catalyst was investigated with a flow reactor, AAS, XPS, and XRD. Excellent reaction performance for CH4-C2H6-O2 to synthesis gas over the LiLaNiO/g-Al2O3 is achieved at 1073 K, obtaining CO selectivity of 90-95% and CH4 conversion of 97%, with a wide range of C2H6 content in the feed and of space velocity. Meanwhile, 100, 200 and 500 h life tests of the LiLaNiO/g-Al2O3 for natural gas-O2 to synthesis gas were also performed. The results indicate that the LiLaNiO/g-Al2O3 catalyst not only possesses excellent reaction performance (CH4 conversion 95%, CO selectivity 98%), good carbon deposition resistance, but also has a relatively stable element component and a stable crystal phase structure during a 500 h life test experiment under conditions of 1123 K, natural gas/O2 ratio of 1.90 and space velocity of 2.710 5 l/(kg h).

Mesoporous spinel MgAl2O4 prepared by in situ modification of boehmite sol particle surface: I Synthesis and characterization of the unsupported membranes

Mesoporous spinel membranes as ultrafiltration membranes were prepared through a novel sol-gel technique. By in situ modification of the sol particle surface during the sol-gel process, control of the material structure on a nanometer scale from the earliest stages of processing was realized. Nano-particles with a chocolate-nut-like morphology, i.e. spinel MgAl2O4 as a shell and g-Al2O3 as a core, were first revealed by HRTEM results. The formation of the spinel phase was confirmed by X-ray diffraction (XRD). N2 adsorption‐desorption results showed that the mesoporous membranes had a narrow pore size distribution.

Catalytic partial oxidation of n-heptane for hydrogen production

Partial oxidation of n-heptane (POH) for hydrogen generation was studied over several catalysts between 700 and 850 °C. Modified Ni-based/γ-Al2O3 catalyst exhibited not only good catalytic activity but also good carbon deposition resistance ability. Under the modified reaction conditions, 100% n-heptane conversion and 93% hydrogen selectivity can be obtained.

Effects of alkali and rare earth metal oxides on the thermal stability and the carbon-deposition over nickel based catalyst

Effects of alkali and rare earth metal oxides on the thermal stability and the carbon-deposition over nickel based catalyst for partial oxidation of methane to syngas were investigated by a series of characterization techniques including flow-reaction, TG, TPO, XPS, XRD and BET. The results indicated that the introduction of Li and La oxides could suppress the carbon-deposition on the nickel based catalyst. LiNiLaO/gamma-Al2O3 catalyst not only possessed excellent reaction performance (CH4 conversion greater than or equal to 96%, CO selectivity greater than or equal to 98%), carbon-deposition resistance and improved the thermal stability of the nickel based catalyst, but also had comparatively stable porous structure and stable crystallity during the 200h life test experiment under the conditions of reaction temperature at 1123K, CH4/O-2 ratio of 1.96 and space velocity of 2.7 x 10(4) l/kg.h.

New methods to prepare perovskite-type La0.8Sr0.2CoO3 catalyst at low temperature

A pure phase perovskite-type composite oxide La0.8Sr0.2CoO3 (LSCO) was prepared by three methods: sol-gel method using EDTA as ligand, environmentaly safe metal-EDTA-cellulose complexing method and metal-citric-cellulose complexing method. The formation processes of LSCO by those methods were investigated by TG-DTA, XRD and IR spectroscopy. The results indicated that when EDTA complexing method was used, at optimized condition, pure phase perovskite-type LSCO was acquired after the precursor was fired at 800 degrees C for 2hr. In the process of forming perovskite LSCO, SrCO3 was formed and calcination temperatures higher than 800 degrees C was needed to get rid of it, similar to the citric complexing method reported. When cellulose was introduced, the minimum calcination temperature to acquire pure phase LSCO was significantly lowered to around 600 degrees C for metal-EDTA-cellulose method and 540 degrees C for metal-citric-cellulose method. Low calcination temperature led to relatively high BET area for 21m(2)/g and 22m(2)/g respectively. But the surface area were significantly reduced to 12.7m(2)/g and 12.1m(2)/g respectively when they were further fired at 620 degrees C for 2hr.

Sustainable Ni catalyst for partial oxidation of CH4 to syngas at high temperature

Effect of alkali and rare earth metal oxides on the stability of nickel based POM catalyst was investigated with flow-reaction, AAS, XPS, and XRD. The 80h life test results indicated that the introduction of Li and La could improve obviously the stability of NiO/γ-Al 2 O 3 , and suppresses the sintering and loss of nickel on NiO/γ-Al 2 O 3 . Meanwhile the 100h, 200h, and 500h life test of LiLaNiO/γ-Al 2 O 3 for natural gas-O 2 to syngas were also performed, respectively. The results revealed that LiLaNiO/γ-Al 2 O 3 catalyst not only possesses excellent reaction performance (CH 4 conversion ∼95%, CO selectivity ∼98%), graphite carbon deposition resistance, but also has comparatively stable pore structure and stable crystalline phase during a 500h life test experiemnt under the conditions of reaction temperature at 1123K, natural gas/O 2 ratio of 1.90 and spaces velocity of 2.7×10 5 L/(kg.h).