Syngas production over La0.9NiyAl11.95-yO19-δ catalysts during C14-alkane partial oxidation: Effects of sulfur and polycyclic aromatic hydrocarbons

Catalytic action of platinum on coke burning

Ni-BTC metal-organic framework loaded on MCM-41 to promote hydrodeoxygenation and hydrocracking in jet biofuel production

The modification of Ni/Al2O3 catalyst by alkaline earth metal oxides including MgO, CaO, SrO and BaO was investigated for hydrogen production from the partial oxidation and reforming of dimethyl ether. MgO modification of the Ni/Al2O3 catalyst enhanced the formation of NiAl2O4. There was only one reduction peak from 700 to 950 °C, which is usually ascribed to the reduction of NiAl2O4. The Ni-containing species which are easily reduced at low temperature were removed. When the MgO modified Ni/Al2O3 was reduced at 750 °C in the performance evaluation, a small amount of Ni was produced from NiAl2O4 to give small and active Ni sites, resulting in better catalytic reforming performance than for the unmodified Ni/Al2O3. The H2 yield of 88% and CO selectivity of 86% was obtained at 800 °C when MgO modified Ni/Al2O3 was adopted as a reforming catalyst, which was combined with 0.5 wt% Pt/Al2O3 to form a dual bed catalysts. The other metal (Ca, Sr, Ba) oxide modification of Ni/Al2O3 catalyst, however, did not enhance the formation of NiAl2O4 as well as MgO, and there were still certain amounts of low temperature reducible NiO species, resulting in a worse catalytic performance than the unmodified Ni/Al2O3. The variation of the amount of MgO modification had no obvious effect on the formation of NiAl2O4. However, the peak reduction temperature of 7.5 wt% MgO modified Ni/Al2O3 in H2-TPR patterns was a little lower than that of 5.0 or 10.0 wt% MgO modified Ni/Al2O3, resulting in a little better catalytic performance by giving more active Ni sites reduced from NiAl2O4 at 750 °C.

The catalytic partial oxidation (CPO) of methane over precious metal catalyst has been shown to be an attractive way to obtain syngas (CO and H2) or H2 which can be converted to clean fuels by Fischer–Tropsch synthesis or employed in fuel cells. However, the presence of sulphur bearing compounds naturally occurring in the fuel, or added as odorants to pipe-line natural gas (approximately up to 10 ppm), can have a detrimental effect on the CPO activity. In this work the effect of sulphur addition on the catalytic partial oxidation (CPO) of methane in the low to moderate temperature regime (300-800 °C) and under self-sustained high temperature (>800 °C) condition was investigated on Rh-based catalysts supported on either La2O3 or SiO2 stabilised γ-Al2O3. Based on the results of catalytic activity measurements and in-situ FT-IR/DRIFT spectroscopic characterisation, as well as TPR/TPD studies, it has been shown that the presence of sulphur can severely suppress the formation of synthesis gas by inhibiting the steam reforming (SR) reactions during the CPO of methane. It was demonstrated that the support material plays a crucial role in the CPO of methane in the low to moderate temperature regime. In the presence of a sulphating support such as La2O3-Al2O3 the partial oxidation reaction was much less inhibited than a less sulphating support such as SiO2-Al2O3. The sulphating support acts as a sulphur storage reservoir, which minimises the poison from adsorbing on or near the active Rh sites where reactions take place. However under the typical operating conditions of methane CPO i.e. at high temperatures and short contact times over structured reactors, sulphur in the feed inhibits the SR reaction by directly poisoning the active Rh sites thus preventing the sulphur storage capacity of the support from showing any beneficial effect on the S-tolerance. Both steady state and transient operation of the CPO reactor were investigated particularly with regards to poisoning/regeneration cycles and low temperature light-off phase. The analysis of products distribution in the effluent and heat balance demonstrated that sulphur reversibly adsorbed on Rh selectively inhibits the SR reaction path to syn-gas production. The extent of SR inhibition is greater when operating in air and diminishes at lower CH4/O2 feed ratios. The poisoning effect was also shown to be independent from the type of sulphur bearing compound and only indirectly affected by the type of catalyst support (La2O3 or SiO2 stabilised alumina) through the value of Rh dispersion. In fact by using in situ DRIFTS experiments of adsorbed CO at room temperature it was found that sulphur acts as a selective poison by preferentially adsorbing on smaller well dispersed Rh crystallites whilst larger metallic Rh sites are mostly unaffected. The adsorption of CO at room temperature before and after S poisoning is schematically represented below. Partial substitution of Rh/La-Al2O3 monolith catalysts with either Pt or Pd did not influence the way S adsorbs on highly dispersed Rh sites. Pd was found to have a detrimental effect on the overall catalytic activity and to be ineffective at improving the S-tolerance. On the other hand the partial substitution of Rh with Pt reduced the detrimental impact of S, which strongly inhibits the SR reaction on dispersed Rh sites but has a much smaller impact on Pt active sites. The improved tolerance of the bimetallic Rh-Pt catalyst against sulphur is due to its higher operating temperature related to the high oxidation activity of Pt which facilitates sulphur desorption from the catalyst and reduces its accumulation.

Incorporating oxophilic metals into noble metal-based catalysts represents an emerging strategy to improve the catalytic performance of electrocatalysts in fuel cells. However, effects of the distance between the noble metal and oxophilic metal active sites on the catalytic performance have rarely been investigated. Herein, we report on ultrasmall (∼5 nm) Pd–Ni–P ternary nanoparticles for ethanol electrooxidation. The activity is improved up to 4.95 A per mgPd, which is 6.88 times higher than commercial Pd/C (0.72 A per mgPd), by shortening the distance between Pd and Ni active sites, achieved through shape transformation from Pd/Ni–P heterodimers into Pd–Ni–P nanoparticles and tuning the Ni/Pd atomic ratio to 1:1. Density functional theory calculations reveal that the improved activity and stability stems from the promoted production of free OH radicals (on Ni active sites) which facilitate the oxidative removal of carbonaceous poison and combination with CH3CO radicals on adjacent Pd active sites.

The selective hydrogenation of alkynes to their corresponding alkenes is an important type of organic transformation, which is currently accomplished by modified palladium catalysts. Herein, we rep...

Environmental and individual PAH exposures near rural natural gas extraction

Ultrafine PdRu Nanoparticles Immobilized in Metal–Organic Frameworks for Efficient Fluorophenol Hydrodefluorination under Mild Aqueous Conditions

Structurally distinct polycyclic aromatic hydrocarbons induce differential transcriptional responses in developing zebrafish

Thermal desorption gas chromatography-mass spectrometric analysis of polycyclic aromatic hydrocarbons in atmospheric fine particulate matter

Fate of PAHs in the post-combustion zone: Partial oxidation of PAHs to dibenzofuran over CuO

Accurate long-range atmospheric transport (LRAT) modeling of polycyclic aromatic hydrocarbons (PAHs) and PAH oxidation products (PAH-OPs) in secondary organic aerosol (SOA) particles relies on the known chemical composition of the particles. Four PAHs, phenanthrene (PHE), dibenzothiophene (DBT), pyrene (PYR), and benz(a)anthracene (BaA), were studied individually to identify and quantify PAH-OPs produced and incorporated into SOA particles formed by ozonolysis of α-pinene in the presence of PAH vapor. SOA particles were characterized using real-time in situ instrumentation, and collected on quartz fiber filters for offline analysis of PAHs and PAH-OPs. PAH-OPs were measured in all PAH experiments at equal or greater concentrations than the individual PAHs they were produced from. The total mass of PAH and PAH-OPs, relative to the total SOA mass, varied for different experiments on individual parent PAHs: PHE and 6 quantified PHE-OPs (3.0%), DBT and dibenzothiophene sulfone (4.9%), PYR and 3 quantified PYR-OPs (3.1%), and BaA and benz(a)anthracene-7,12-dione (0.26%). Further exposure of PAH-SOA to ozone generally increased the concentration ratio of PAH-OPs to PAH, suggesting longer atmospheric lifetimes for PAH-OPs, relative to PAHs. These data indicate that PAH-OPs are formed during SOA particle formation and growth.

New insights into the catalytic mechanism of VOCs abatement over Pt/Beta with active sites regulated by zeolite acidity

The degradation of polycyclic aromatic sulfur hydrocarbons (PASHs) in aqueous solutions due to sonochemical processes was studied. Benzothiophene (BT), and dibenzothiophene (DBT) in addition to two polycyclic aromatic hydrocarbons, namely phenanthrene (Phe) and naphthalene (Nap) were compared. Results showed that all polycyclic aromatic compounds were decomposed rapidly following a pseudo‐first‐order kinetics upon ultrasonic irradiation in aqueous solutions. The rate constant increased with increasing pH and decreased with increasing initial benzothiophene concentration. Whereas, for temperature, the rate increased with temperature up to 50°C then decreased upon further increase in temperature above 50°C. Hydroxybenzothiophenes, dihydroxy‐benzothiophenes, and benzothiophene‐dione were identified as major intermediates. Also evolution of carbon dioxide and sulfite was observed. Hydroxyl radicals play the major role in the decomposition of PASHs. The toxicity of sonochemically treated solutions was evaluated by monitoring the respiration rate of E. coli. Results indicate that a sonochemically treated benzothiophene sample improved the respiration rate of E. coli compared to an untreated sample.

The partial oxidation of methane was studied on Pt/Al2O3, Pt/ZrO2, Pt/CeO2 and Pt/Y2O3 catalysts. For Pt/Al2O3, Pt/ZrO2 and Pt/CeO2, temperature programmed surface reaction (TPSR) studies showed partial oxidation of methane comprehends two steps: combustion of methane followed by CO2, and steam reforming of unreacted methane, while for Pt/Y2O3 a direct mechanism was observed. Oxygen Storage Capacity (OSC) evaluated the reducibility and oxygen transfer capacity of the catalysts. Pt/CeO2 catalyst showed the highest stability on partial oxidation. The results were explained by the higher reducibility and oxygen storage/release capacity which allowed a continuous removal of carbonaceous deposits from the active sites, favoring the stability of the catalyst, For Pt/Al2O3 and Pt/ZrO2 catalysts the increase of carbon deposits around or near the metal particle inhibits the CO2 dissociation on CO2 reforming of methane. Pt/Y2O3 was active and stable for partial oxidation of methane, and its behavior was explained by a change in the reaction mechanism.