Dibenzothiophene hydrodesulfurization using in situ generated hydrogen over Pd promoted alumina-based catalysts

Catalytic hydrodesulfurization (HDS) of dibenzothiophene (DBT) was carried out in a temperature range of 320-?400 °C using in situ generated hydrogen via steam reforming of ethanol and the effect of some organic additives was studied for the first time. Four kinds of alumina-based catalysts, i.e. Co?-Mo/Al₂O₃, Ni-Mo/Al₂O₃ and their corresponding Pd promoted catalysts Pd-?Co-?Mo/Al₂O₃ and Pd-?Ni-?Mo/Al₂O₃, prepared through incipient impregnation method, were used for the desulfurization process. Catalytic activity was investigated in a batch autoclave reactor in the complete absence of external hydrogen gas. Experiments showed that organic additives like diethylene glycol (DEG), phenol, naphthalene, anthracene, o-xylene, tetralin, decalin and pyridine can affect the HDS activity of the catalysts in different ways, and only naphthalene is inhibitive for the catalytic activity towards HDS. The results showed that Ni-based catalysts are more active than Co-based ones while Pd shows a high promotion effect. DBT conversion of up to 97% was achieved with Pd-?Ni-?Mo/Al₂O₃ catalyst at 380 °C temperature and 13 h reaction time. Catalyst systems followed the HDS activity order of: Pd-?Ni-?Mo/Al₂O₃ > Ni-?Mo/Al₂O₃ > Pd-?Co-?Mo/Al₂O₃ > Co?-Mo/Al₂O₃ at all conditions. Qualitative analysis of the products stream was carried out using GC?-MS technique. The present HDS process using in situ generated hydrogen might be applied as an alternative approach for the catalytic HDS of DBT on industrial level due to its cost effectiveness, mild operating conditions and high activity of the catalysts.     

Effect of the nitrogen heterocyclic compounds on hydrodesulfurization using in situ hydrogen and a dispersed Mo catalyst

The hydrodesulfurization (HDS) of the highly refractory sulfur-containing compounds, dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT), and the effect of the basic and non-basic nitrogen heterocyclic compounds, such as quinoline and carbazole, on HDS using a dispersed unsupported Mo catalyst and in situ generated hydrogen were studied. Experimental results indicated that the dispersed unsupported Mo catalyst was effective for the HDS of 4,6-DMDBT in a mixture containing DBT. The direct desulfurization pathway (DDS) was the preferred pathway for the HDS of DBT while the hydrogenation pathway (HYD) was the preferred pathway for the HDS of 4,6-DMDBT under our experimental conditions. A strong inhibitive effect of the basic quinoline or the non-basic carbazole on the HDS of each of the sulfur-containing compounds was observed. The DDS and HYD pathways in the HDS of the refractory sulfur-containing compounds were affected to a different extent by the nitrogen-containing compounds, suggesting that different active sites were involved in these two reaction pathways.     

Study of the water gas shift reaction on Fe in a high temperature proton conducting cell

The water gas shift (WGS) reaction was studied in a double-chamber high temperature proton conducting cell (HTPC). The proton conductor was a strontia–ceria–ytterbia (SCY) disk of the form: SrCe_0.95Yb_0.05O₃₋ and the working electrode was a polycrystalline Fe film. The reaction temperature and the inlet partial pressure of CO varied between 823 and 973 K, and between 1.0 and 10.6 kPa, respectively. The inlet partial pressure of steam (P_H2O) was kept constant at 2.3 kPa. An increase in the production of H₂ was observed upon “pumping” protons away from the catalyst surface. The Faradaic efficiency (Λ) was lower than unity, indicating a sub-Faradaic effect. The highest value of rate enhancement ratio (ρ) was approximately 3.2, at T = 823 K. The proton transport number (PTN) varied between 0.45 and 1.0. An up to 99% of the produced H₂ was electrochemically separated from the reaction mixture.     

Hydrodenitrogenation of Quinoline Over a Dispersed Molybdenium Catalyst Using in situ Hydrogen

Hydrodenitrogenation (HDN) of quinoline using a Mo-based dispersed catalyst was studied in a batch reactor using H₂ generated in situ via the water gas shift reaction. In situ H₂ was found to be more active for HDN than externally supplied H₂. Both water and H₂S have an effect on HDN.     

Effect of Catalyst Supports on Water‐Gas Shift Reaction at Ultrahigh Temperatures Using Syngas

Monometallic and bimetallic catalysts (Pt, Ni, and Pt‐Ni) with single support (Al₂O₃, TiO₂) and composite support (CeO₂/Al₂O₃, CeO₂/TiO₂) were prepared and tested for water‐gas shift reaction in a tubular quartz reactor. Syngas and steam with different steam‐to‐carbon ratios served as feedstock. The operating pressure was fixed while the reaction temperature was varied. The measured results indicated that the monometallic Ni/Al₂O₃ catalyst exhibits the lowest CO conversion and H₂ yield as compared with other catalysts. About the same CO conversion can be obtained from Pt and Pt‐Ni catalysts with single or composite support. However, higher H₂ yield can be achieved from the TiO₂‐supported catalyst compared with those supported by Al₂O₃. The experimental data also indicated that good thermal stability can be reached for the Pt‐based catalysts studied.     

Effect of the order of potassium introduction on the texture and activity of Mo/Al2O3 catalysts in water gas shift reaction

The effect of deposition and order of potassium introduction on the texture and activity of Mo/γ-Al₂O₃ catalysts in water gas shift (WGS) reaction was investigated. The samples were synthesised by incipient wetness impregnation of the carrier with aqueous solutions of the corresponding salts followed by drying and calcination after each deposition step. The prepared catalyst precursors were sulphided at 400°C for 2 h with 6% H₂S in H₂ before testing in WGS reaction in a glass flow apparatus at 400°C under atmospheric pressure.

The results show that potassium deposition alone on the bare γ-Al₂O₃ (sample K/Al₂O₃) decreases the specific surface after calcination by blocking the constrictions between the pores in the primary porous texture. In the WGS reaction conditions part of the pores are deblocked and a redistribution in the pore volumes occurs.

The deposition of the Mo (sample Mo/Al₂O₃) also results in a decrease in both specific surface and total pore volume with respect to the bare support. However after catalytic activity test no substantial changes in its texture were observed.

The addition of K to the Mo (sample KMo/Al₂O₃) leads to nonuniformity in distribution of molybdenum–oxygen entities due to partial migration of the MoO_x species to the external surface. The specific surface is not changed during the reaction test.

The deposition of Mo on K/Al₂O₃ contributes to the uniform distribution of oxomolybdenum species in the porous texture of the support. This uniformity is preserved to a high extent in the catalytic reaction as well. The activity in the synthesised samples in the WGS reaction decreases in the order MoK/Al₂O₃ > Mo/Al₂O₃ > KMo/Al₂O₃.     

Effect of hydrogen on reaction intermediates in the selective catalytic reduction of NOx by C3H6

Selective catalytic reduction of NO_x by C₃H₆ in the presence of H₂ over Ag/Al₂O₃ was investigated using in situ DRIFTS and GC–MS measurements. The addition of H₂ promoted the partial oxidation of C₃H₆ to enolic species, the formation of –NCO and the reactions of enolic species and –NCO with NO_x on Ag/Al₂O₃ surface at low temperatures. Based on the results, we proposed reaction mechanism to explain the promotional effect of H₂ on the SCR of NO_x by C₃H₆ over Ag/Al₂O₃ catalyst.     

Effect of hydrogen peroxide on the destruction of organic contaminants-synergism and inhibition in a continuous-mode photocatalytic reactor

The effect of hydrogen peroxide on the photocatalytic degradation of organic contaminants in water was investigated using a TiO₂-rotating disk photocatalytic reactor (RDPR) operated in a continuous-mode and at steady state. The experiments were performed at pH 3.0, in the presence of near-UV radiation, and using 4-chlorobenzoic acid (4-CBA) as a model non-volatile organic contaminant at influent concentration of 300 μmol l⁻¹. Experiments were performed at concentrations of hydrogen peroxide in the range 0–10.74 mmol l⁻¹. Addition of hydrogen peroxide at small concentrations (<2 mmol l⁻¹) had a synergistic effect and increased considerably the rates of photocatalytic reactions. An optimum influent hydrogen peroxide concentration was observed at 1.6 mmol l⁻¹, which caused an increased in the rates of 4-CBA degradation and total organic carbon (TOC) mineralization by 1.72 and 2.13 times, respectively. This corresponded to an optimum oxidant to contaminant molar ratio of 5.33. At higher concentrations, hydrogen peroxide was found to cause an inhibiting effect on the photocatalytic reactions. The synergistic and inhibiting effects of hydrogen peroxide were rationalized based on the reaction rate constants between relevant radical species.