Deactivation and regeneration of Ni catalyst during steam reforming of model biogas: An experimental investigation

This paper presents detailed study of biogas reforming. Model biogas with different levels of H₂S is subjected to reforming reaction over supported Ni catalyst in a fixed bed reactor at 700 °C and 800 °C. In order to understand the poisoning effects of H₂S the reactions have been initially carried out without H₂S in the feed stream. Three different H₂S concentrations (20, 50 and 100 ppm) have been considered in the study. The H₂O to CH₄ ratio is maintained in such as way that CO₂ also participates in the reforming reaction. After performing the poisoning studies, regeneration of the catalyst has been studied using three different techniques i) removal of H₂S from the feed stream ii) temperature enhancement and iii) steam treatment. Poisoning at low temperature is not recoverable just by removal of H₂S from the feed stream. However, poisoning at high temperature is easily reversed just by removal of H₂S from the feed stream. Unlike some previous reports by Li et al. (2010) and Rostrup-nielsen (1971) [1,2], catalyst regeneration is achieved in shorter time frames for all the regeneration techniques attempted.     

Highly efficient catalytic pyrolysis of biomass vapors upgraded into jet fuel range hydrocarbon-rich bio-oil over a bimetallic Pt–Ni/γ-Al2O3 catalyst

Catalytic pyrolysis is an effective method for converting biomass to value-added chemicals. However, the development of cost-effective catalysts remains a major challenge. In this study, a highly efficient bimetallic Pt–Ni catalyst (Pt to Ni ratio = 0:1, 2:1, 1:1, 1:2, 1:0) was fabricated and used for catalytic biomass pyrolysis upgrading into hydrocarbon-rich bio-oil with pyrolysis-gaschromatography × gaschromatography/mass spectrometry (Py-GC1 GC/MS). The product yield and selectivity of upgraded bio-oil, thermal properties, kinetic and deactivation mechanisms were also determined to investigate the reaction mechanism. It was determined that Pt addition strengthened the NiO and alumina interaction and improved nickel dispersion, promoting CO hydrogenation. Bimetallic catalysts had a higher stability and activity owing to synergistic action of platinum and nickel on γ-Al₂O₃, and the surface oxygen vacancies were derived from the electron transfer of Pt to Ni and the higher number of super acid-base sites, which inhibited coke deposition. In addition, the higher valence Pt (Pt²⁺) in the catalyst was favorable for decarboxylation and hydrodecarbonylation reactions. Various metal ratios were employed, and the Pt–Ni/Al = 1:2 catalyst exhibited an excellent catalytic performance, achieving highest peak areas of desired hydrocarbons and aromatic hydrocarbons at 52.67% and 40.25%, respectively, and the lowest peak area of deposited coke at 7.26%, along with a 13.98% weightloss rate.     

Copper manganite as a catalyst for the PROX reaction. Deactivation studies

CuMn₂O₄ nanocatalysts synthesised by silica aquagel confined co-precipitation were analysed for the preferential oxidation of CO at different temperatures and concentration conditions. The catalysts show a higher activity than copper–ceria catalysts synthesised by the same method but, like these, they suffer from slow deactivation during the reaction. Surface analysis (FTIR and XPS) was used to unravel the deactivation mechanisms. Gradual reduction of the catalysts by the carbon monoxide present in the PROX stream was concluded to be the main cause of deactivation.     

THE FLAT LAMINAR OPPOSED JET DIFFUSION FLAME:A NOVEL TOOL FOR KINETIC STUDIES OF TRACE SPECIES FORMATION

The flat laminar opposed jet diffusion flame was used to determine net rates of formation and destruction of nitric oxide under a wide range of temperatures and local fuel concentrations. In order to accomplish this the theoretical model of this flame was first validated with respect to experimental data on major species and temperature. Then the measured NO and temperature profiles were utilized in conjunction with the species conservation equation to obtain the desired result.     

Isomerization of n-butane: Conversion as a function of sulfate loading on sulfated zirconia catalysts

Sulfur loading on a sulfated zirconia catalyst was studied as a function of H 2 SO 4 concentration. The resulting catalytic activity was tested using the isomerization of n -butane as a reaction probe at 200°C. Optimum catalytic activity was observed for a catalyst prepared using 0.5 N H 2 SO 4 . The amount of carbon required to completely deactivate the catalyst was determined using a TGA/FTIR technique. For all of the catalysts synthesized in this study it was found that two active sulfate sites were poisoned by a single deposited carbon atom. Using this information, an active site composed of two coupled sulfate sites, perhaps a surface pyrosulfate site, is suggested. Using a TGA/FTIR technique it was found that the number of catalytically active sulfate sites never exceeded 14% of the total sulfate loading. These results were also supported by calorimetric studies.     

Water tolerance of DeNOx SCR catalysts using hydrocarbons: Findings, improvements and challenges

The recent developments on the effect of H₂O on deNO_x performance of a variety of SCR catalysts selectively removing NO_x by hydrocarbons in excess oxygen have been reviewed. In particular, the water tolerance of the catalyst is summarized to illustrate a common deactivation behavior of SCR catalyst for the reduction of NO by hydrocarbons under wet feed gas mixture. Earlier proposals elucidating the possible cause of the catalyst deactivation under wet conditions are discussed, focusing mainly on the catalyst characteristics. A promising way, which can improve the water tolerance and the hydrothermal stability of zeolite-based SCR catalyst, is also described.     

Isobutane alkylation with C4 olefins on a sulfonic solid acid catalyst system based on laminar clays

Natural clays were modified by means of the controlled attack of strong Brönsted acids in aqueous solution. The variations of the surface acidity of the solids, followed by IR of adsorbed pyridine and hammett indicators, indicated a population of Brönsted type sites above 800 μ mol/g, while the surface area increased from 23 up to 105 m²/g. A series of solids (ATZ-L, ATZ-A and ATZ-G) was activated using trifluoromethanesulfonic acid (CF₃SO₃H), then evaluated at the bench scale in a fixed bed reactor, both in liquid and gas phase, using an iC₄/C₄⁼ molar ratio, which led to 5.5% trimethylpentanes (TMP) against 35.9% of C₈⁼ and 53.4% of heavier C₉⁺ products for the catalysts (ATZ-L) having higher acid strength, i.e. Ho≈−9.3. For the solids having a moderate surface acid strength (Ho≈−4.4) the activation rate after 12 h runs was about 70%, but the solids having a higher acid strength, i.e. Ho=−5.6 and −9.3, showed a deactivation rate almost null after 24 h runs.     

Structural and morphological study of metal deposition on an aged hydrotreating catalyst

The results of NiMo/γ-Al₂O₃ hydrodemetalation catalyst deactivation in a long-term test are presented. A residue from Maya crude has been processed in a continuous hydroprocessing unit provided with a trickle-bed reactor (TBR) at 648 K, 10 MPa H₂ pressure, 1 l/h g_cat LHSV and 0.2 kg/kg ratio H₂/oil. Samples of catalyst from 100, 1100, 2100 and 3100 h on-stream have been characterised by Ni, V and Mo determination and the evolution of the structural and morphological characteristics of these samples has been followed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) using electron backscattering detector and microanalysis by dispersion of energies (EDS). XRD and XPS results have confirmed the presence of sulphide phases with a stoichiometry close to (V, Ni, Fe)₃S₄. Metal deposition profiles of vanadium have shown high concentrations in the edges while nickel deposition profiles have been more uniform. The shape of these profiles has indicated that for vanadium removal reactions, the metal deposition process becomes more diffusion rate limited, resulting in a less deep penetration into the catalyst pellet.     

FC-18催化剂的再生利用

采用物理吸附仪、X光衍射仪(XRD)、红外光谱(IR)、等离子发射光谱(ICP)、无机分析、元素分析仪对再生前后FC-18催化剂的物化性质和性能变化进行了测试和表征,探讨了催化剂失活的原因。结果表明,与新鲜催化剂相比,再生后FC-18催化剂的孔容和平均孔径有所增大,比表面积及酸度均有所降低;再生后FC-18催化剂表面无明显活性金属聚结现象,碳、硫烧除效果良好;催化剂活性评价结果表明,再生后FC-18催化剂的活性略低于新鲜催化剂,但仍可满足企业生产需求。     

Catalytic wet air oxidation with a deactivating catalyst analysis of fixed and sparged three-phase reactors

A comparative analysis is made for a trickle-bed reactor, a packed-bubble column, a three-phase fluidized bed and a slurry-bubble column with an active and moderately deactivating catalyst for the wet oxidation at high pressure and temperature of organic-containing aqueous wastes. Compared to other mature industrial sectors where multiphase reactors are prevalent, the design of three-phase catalytic reactors for wet air oxidation processes is still at an emerging stage. This paper discusses, from a multiphase reactor engineering perspective, the design of such contactors by setting an exhaustive modeling framework of catalytic wet oxidation in which the molecular, particle and reactor scales are integrated. The simulation results indicate that when wet oxidation is liquid-reactant limited, packed-bubble columns outperform trickle beds, whereas slurry-bubble columns are the most vulnerable to “coke” deactivation.