Probability of chain growth in coke formation on metals and on supports during catalytic reforming over Pt, Pt-Sn and Pt-Sn-K catalysts mixed physically with Al2O3

The main goal of this contribution was to study the probability of chain growth of coke on metal sites and on support sites for hexane dehydrogenation. The coke structure of the catalysts examined by IR was found to have the aromatic structure. Soxhlet extraction coupled with GC-14B (DB1 column) analysis was mainly employed for coke composition analysis and determination of the probability of chain growth (alpha value). It was found that the soluble coke was mainly composed of C₈–C₁₂ on both sites. Interestingly, the probabilities of chain growth on both sites were identical. However, the extracted coke on the metal site was more easily removable and had lower carbon numbers than that on the support site. Moreover, the addition of promoter, especially of K promoter, was sensitive to inhibit the probability of chain growth, resulting in the reduction of the amount of coke.     

Characterization and performance of Pd-La/spinel catalyst for preparation of 2,6-diisopropylaniline

The Pd-La/spinel catalyst for the preparation of 2,6-diisopropylaniline (2,6-DIPA) by gas-phase amination of 2,6-diisopropylphenol (2,6-DIPP) has been studied. The catalysts before and after reaction were characterized by BET, XRD, differential thermal analysis (DTA)-thermo gravimetric analysis (TGA), FTIR, and NH₃-TPD techniques. The DTA study results show two kinds of coke deposited on the metal and support of Pd-La/spinel catalyst, and they are combusted at about 242 and 324 °C, respectively. The XRD and FTIR spectra of the Pd-La/spinel catalyst show that the coke contains the aromatic and aliphatic rings, alkyl groups, polynuclear aromatic system, hydroxyl groups, and amine groups. The reason for catalyst deactivation can be expressed as follows: coke formed on palladium metals may move from metal to the interface or boundaries of metal-support and acid sites of the support where further dehydrogenation and polymerization are occurring. The H₂ plays a key role in retarding coke formation, but must be in suitable amount to get relatively high selectivity. The rare earth promoter La not only promotes the activity and selectivity by retaining Pd species in the metallic state, but also decreases the formation of carbon by neutralizing the strong acid sites on the catalyst.     

不同配比碱金属化合物对焦炭反应性的影响

通过将一定粒度焦炭浸入不同配比碱金属化合物（K2CO3＋Na2CO3）溶液的方法在实验室制得焦样,用热重天平对焦样进行了焦炭反应性实验及SEM扫描电镜和能谱分析。研究结果表明,不同配比碱金属K、Na复合催化剂催化效果不同,K2CO3对焦炭溶损反应的催化作用贡献较大,焦炭溶损反应主要催化作用时间为前10min,浸碱焦炭试样中K、Na含量随碱溶液中K、Na含量增加而增加。     

沸腾床渣油加氢处理催化剂失活研究

沸腾床催化剂失活主要是由于金属和焦炭沉积导致的,同时在沸腾状态下催化剂的物理和机械性质也发生了改变。使用后的催化剂向小的粒度分布方向偏移;催化剂沉积了大量的金属和焦炭,使催化剂的堆积密度增加,同时导致催化剂的孔结构、酸性质发生了变化。失活催化剂沉积的金属和焦炭在颗粒内外分布均匀,表明催化剂利用率较高。     

Pore structure alteration of porous carbon by catalytic coke deposition

The feasibility of preparing Carbon Molecular Sieve (CMS) by tailoring pore structure of activated carbon under catalytic cracking of benzene has been examined. In this method, benzene vapour was cracked over metal-impregnated activated carbon particles at 523–773 K. Among the metal catalysts tested, only cobalt exhibited significant cracking activity toward benzene. In this range of temperature coke was originated on the metal surface only, therefore an excessive coke deposition as indicated in non-catalytic process was not observed. The amount of coke and the site of deposition in the pore network were determined to some extent by the metal loading as well as the rate of benzene cracking. Raman spectra indicated that the coke produced was less amorphous than those produced in non-catalytic processes. Only a small loss in micropore volume and surface area was observed after the coke deposition process. The CMS produced was tested for its adsorption characteristics of carbon dioxide and methane. The improvement in the CO₂/CH₄ kinetic selectivity was observed.     

Petroleum coke conversion behavior in catalyst-assisted chemical looping combustion

Efficiently using petroleum coke as fuel and reducing carbon emission meanwhile have become attractive in oil processing industry. The paper is focused on the application of Chemical Looping Combustion (CLC) with petroleum coke, with the purpose of investigating its combustion performance and effects of potassium. Some experiments were performed in a laboratory scale fluidized bed facility with a natural manganese-based oxygen carrier. Experimental results indicated that the coke conversion is very sensitive to reaction temperature. The present natural manganese-based oxygen carrier decorated by K has little effect on the improvement of coke conversion. XRD, SEM–EDX, and H₂-TPR were adopted to characterize the reacted oxygen carrier samples. After being decorated by K, the oxygen carrier's capacity of transferring oxygen was decreased. A calcination temperature above the melting point of K₂CO₃ (891 °C) shows better oxygen transfer reactivity in comparison to the one calcined at a lower temperature. The natural oxygen carrier used in the work has a high content of Si, which can easily react with K to form K(FeSi₂O₆). Further, irrespective of reaction temperature, the coke conversion can be significantly enhanced by decorating the coke with K, with a demonstration of remarkably shorter reaction time, faster average coke gasification rate and higher average carbon conversion rate.     

Oxidative decomposition of dichlorodifluoromethane (CFC-12) in the presence of butane over Tungsten(VI) oxide catalysts supported on alumina–zirconia

The oxidative decomposition of dichlorodifluoromethane (CFC-12) in the presence of butane was investigated with tungsten(VI) oxide catalyst supported on alumina–zirconia. In this reaction, it is considered that CFC-12 might react with water formed by the combustion of butane at high temperatures above 773 K, and that most of CFC-12 might react directly with oxygen at low temperatures below 723 K. The CFC-12 conversion over the tungsten(VI) oxide catalyst decreased with the passage of time on stream at low temperatures below 673 K. This deactivation of the catalyst was attributed to the coke deposition on the acid sites of the catalyst as well as to the fluorination of the acid sites. The CFC-12 conversion at 4 h on stream became higher when the catalyst was loaded with platinum or palladium, but the butane conversion was not changed by loading. The amount of the coke deposited on platinum- or palladium-loaded tungsten(VI) oxide catalysts, which exhibited a high CFC-12 conversion at 4 h on stream, was very small. Accordingly, the depression of the catalyst deactivation might be caused by the combustion of the coke deposited on the acid sites due to the catalysis of platinum and palladium.     

Benzyl diethyl phosphite as a coke inhibitor during naphtha pyrolysis. tubular reactor studies

The effectiveness of benzyl diethyl phosphite as a coke inhibitor during naphtha pyrolysis was investigated in a tubular reactor at 1073 K and atmospheric pressure. Significant reduction in the coking rate was achieved by adding benzyl diethyl phosphite to the feed. The effect of toluene, methylcyclohexane, l-octene and carbon disulfide on the rate of coke formation was also investigated. Toluene enhanced the rate of coke formation significantly, whereas with methylcyclohexane and l-octene the increase was less appreciable. Carbon disulphide decreased the amount of coke deposited initially, but with increasing run time the asymptotic coking rates were found to be higher than for straight-run naphtha. The yields of propylene, 1,3-butadiene and butenes increased on addition of carbon disulphide.     

Effects of carbon on the sulfidation and hydrodesulfurization of CoMo hydrating catalysts

The effects of carbon addition on CoMo catalyst performance for sulfidation and hydrodesulfurization (HDS) were investigated. The carbon-containing catalyst was prepared by impregnation of γ-Al₂O₃ support with NH₃ aqueous solution containing Co(NO₃)₂·6H₂O, (NH₄)₆Mo₇O₂₄·4H₂O and ethylenediamine. The results indicated that the incorporation of proper carbon on CoMo catalyst can improve its HDS performance. The carbon species on the catalyst were characterized by temperature-programmed oxidation and reduction, temperature-programmed desorption of ammonia and ultraviolet-visible diffuse reflectance spectra. Two forms of carbon species were differentiated: one is spread over the catalyst surface, similar to coke formed from reaction; the other interacts with active phase as an intermediate support. The carbon species acting as intermediate support may decrease the interaction of active metals with support, which enhances the sulfidation and HDS activities of CoMo catalyst. This work was presented at the 7th China-Korea Workshop on Clean Energy Technology held at Taiyuan, Shanxi, China, June 26–28, 2008.     

担载钌催化剂的CO吸附和加氢反应性能

通过ＣＯ脉冲化学吸附以及对吸附态ＣＯ和ｃｏ＋Ｈ＿２反应进行程序升温表面反应（ＴＰＳＲ），发现１％Ｒｕ／ｓｉＯ＿２和１％Ｒｕ／ＡＬ＿２Ｏ＿３催化剂的ＣＯ吸附量随焙烧温度的升高而降低。且根据５１３Ｋ和室温吸附ｃｏ的ＴＰＳＲ不同，认为存在两类不同活性中心。Ⅰ类中心：金属钌与载体的相互作用弱，易吸附ＣＯ；Ⅱ类中心：金属与载体的相互作用强，较难吸附ＣＯ。随焙烧温度升高，金属与载体作用增强，Ⅱ类中心增多。在微型流动反应器上ＣＯ中压加氢发现经６７３Ｋ焙烧的样品的活性及长链烃的生成量和烯／烷比均大于１２０℃烘干的样品，因此认为，Ⅰ类中心为加氢中心，Ⅱ类中心为链增长中心。     

Transfer-hydrocracking of vacuum residue

Hydrocracking of Arabian Heavy vacuum residue conducted in the presence of metal supported active carbon catalyst gave large amount of distillates (70%) with small hydrogen consumption. Especially, the Yalloum coal derived active carbon catalyst showed high cracking activity. The yield of asphaltene in the product oil was very low, whereas the coke yield was relatively high. In the metal-free active carbon system, the coke yield and the content of olefins, sulfur compounds and asphaltene in the product oil were higher than those of the metal-supported active carbon system. These results suggest that asphaltene in feed oil was adsorbed on the metal supported active carbon catalyst and was decomposed or dehydrogenated on it to form coke and hydrogen atoms. The hydrogen atoms formed migrated on the carbon surface to reach the metal site and transferred to free radicals, olefins or organo sulfur compounds.     

Roles of Pt and alumina during the combustion of coke deposits on propane dehydrogenation catalysts

Temperature programmed oxidation of coke deposited on Pt based propane dehydrogenation catalysts reveals that the deposited coke can be categorised into three groups according to their burning temperatures. When coke was separated from the catalyst, however, only one TPO peak could be observed. Experimental results suggest that γ-Al₂O₃ enhances the coke burning process by increasing coke surface area contacts to oxygen. Pt may also act as a catalyst for the coke combustion reaction. Experiments also show that changing dehydrogenation reaction temperature, variation of H₂/HC ratios, addition of only Sn or Sn and an alkali metal (Li, Na and K) can significantly affect the amount of each coke formed. Sample weight used in the temperature programmed oxidation (TPO) experiment also affects the resolution of TPO spectrum.     

Catalytic oxidization of SO2 from incineration flue gas over bimetallic Cu–Ce catalysts supported on pre-oxidized activated carbon

To improve the deep sulfation of alumina support, the inertness material activated carbon was used as an alternative support for copper/cerium catalysts to remove SO₂ from incineration flue gas which contained other air pollutants such as NO_X, CO, CO₂, HCl, carbon particulates, and heavy metal vapor. During the 473–820 K, the AC support showed no retention of SO₂. However, the metal Pb composed in the flue gas exhibited the toxic characterization to M/AC catalysts, which was due to the outer orbitals of d subshell all paired.     

Hydrodesulphurization activity and coking propensity of carbon and alumina supported catalysts

Co—Mo, Fe and Mo catalysts were prepared on alumina and carbon supports. The reactivity of sulphided catalysts for thiophene hydrodesulphurization and the propensity for coke deposition of nonsulphided catalysts during propylene cracking and anthracene carbonization were measured. The hydrodesulphurization activity of Co—Mo and Fe catalysts increased in the order γ-Al₂O₃ < C-black composite < active carbon. For a given metal, considerable differences in activity were found both between the carbons and alumina and between the carbons themselves. Possible reasons for the different activities include the influence of the supports on metal dispersion and the presence of impurities in the carbons. For alumina supported catalysts there is a correspondence between hydrodesulphurization activity and coking propensity. On carbon supported catalysts, the rates of carbon deposition appear insensitive to the nature of the metal component(s) whereas hydrodesulphurization activity is not. Thus it is possible to enhance the latter without attendant increases in the susceptibility to coke-forming reactions. Increasing Mo loading from 0–12 wt% was found to substantially increase the rate of carbon deposition on alumina, whereas the effect on a carbon support was comparatively small. This behaviour appears to relate to the inherent support acidity and its modification on metal addition.     

Further insights into the Ru nanoparticles-carbon interactions and their role in the catalytic properties

Temperature-programmed reduction (TPR) and CO adsorption microcalorimetry along with the catalytic behaviour in the n-butane/H₂ test reaction were performed in order to determine the specific interactions of Ru nanoparticles supported on different carbon materials. Aspects such as the porous structure and surface chemistry (presence and elimination of surface oxygen functional groups) of the carbon material, or the effect of the metal precursor (e.g. presence of residual chlorine) on the final metal dispersion and on the surface structure of the Ru nanoparticles have been studied.The results obtained confirm that surface oxidation of the support along with the nature of the Ru precursor affects the distribution of the metal precursor over the support (and, consequently, the final ruthenium dispersion) and also the surface site distribution. Besides, elimination of the surface oxygen functional groups of the carbon material, during the reduction treatments of the fresh catalyst samples, leads to surface reconstructions on the Ru nanoparticles that seem to expose different crystallographic planes. The presence of residual chlorine leads to electron deficient Ru sites, and this modifies the CO chemisorption heats and affects the catalytic properties in the n-butane/hydrogen test.     

Syngas production via CO2 reforming of methane using Co-Sr-Al catalyst

The effect of addition of strontium in Co based catalysts during CO₂ reforming of methane was investigated in the temperature range 500–700 °C. The Co/γ-Al₂O₃ supported catalysts with strontium as a promoter (0–2.25 wt%) were prepared by incipient wet impregnation method. Numerous techniques such as N₂ adsorption–desorption isotherm, H₂ temperature-programmed reduction (TPR), temperature-programmed desorption (TPD), X-ray diffraction (XRD), thermogravimetric analysis (TGA), Transmission Electron Microscopy (TEM), pulse chemisorption and temperature-programmed oxidation (TPO) were applied for characterization of fresh and spent catalysts. The results of characterizations and catalyst activity test revealed that introduction of Sr in Co/γ-Al₂O₃ catalyst had significant effect on stability and coke suppression. The Sr addition improves the metal–support interaction as well as enhances the Lewis basicity of the catalyst. The improvement in basicity helps the chemisorption and dissociation of CO₂ over the catalyst which in turn reduces carbon deposition.     

Challenges, catalyst technology and catalytic solutions in resid FCC

The concurrent evolution of resid fluid catalytic cracking (RFCC) processes and catalyst technology over the years is discussed. Resid FCC catalysts today are designed making use of the following features: (a) High activity, selectivity and metals resistant zeolites; (b) Highly accessible catalyst architecture for optimal site utilization, bottoms cracking, Conradson carbon residue (CCR) conversion and easy stripping; and (c) Specially designed metal-support interaction systems to reduce the detrimental effects of metal contaminants. The future will require even more robust RFCC catalyst systems. These catalyst systems should be very accessible and effective in cracking large hydrocarbon molecules and should have the capability to handle contaminants such as metal-, sulfur-, and nitrogen-compounds. Conversion of CCR to non-coke components will be crucial in order to reduce the delta coke and hence improve the processability of heavier resids. Processability here is meant not only in terms of coke and heat balance considerations, but also involves avoiding fouling of the unit hardware by unconverted heavy hydrocarbons and coke precursors. Last, but not the least, present and future catalyst technology must be formulated and adapted to the specific commercial process unit needs and constraints, thus leading to the most cost effective solution for the refiner.     

Effect of heat treatment of activated carbon supports on the loading and activity of Pt catalyst

The study has been done on the effect of heat treatment of activated carbon at 1573-1773 K on its structural and electronic properties as a catalyst support. The X-ray diffraction result indicated that a partly graphitized structure was formed when the activated carbon was heated to a high temperature (1673 K). From the X-ray photoelectron spectroscopy result, it was found that Pt⁰ concentration was increased, but PtO and PtO₂ concentrations were decreased with an increase in the heat treatment temperature. From the van Dam’s model applied to this result, it might be concluded that more “π-sites” are created as the heat treatment temperature becomes higher. From the CO-chemisorption result, the highest loading was observed in case of Pt/AC1673 sample. This improved loading ability could be explained by the special interaction of the graphitic planes (π-sites) with the metal particles. Based on the catalytic activity, CO-chemisorption and XPS results, it is concluded that the well-loaded Pt⁰ species mainly contribute to the catalytic activity. Moreover, it was found that different degrees of graphitization of heat treated activated carbon could cause different surface Pt⁰ and improve the resistance of carbon support against gasification under air oxidation.     

铂系低碳烷烃脱氢催化剂研究进展

综述了近年来国内外铂系低碳烷烃脱氢催化剂的技术现状与研究进展。首先从热力学角度论述了低碳烷烃脱氢反应与相关副反应的反应机理,随后分别从活性位点性能与催化脱氢的关系,氧化铝、分子筛等载体的作用,以及锡、碱金属、碱土金属、过渡金属等助剂改性对催化剂的影响等3个方面分析了铂系低碳烷烃脱氢催化剂的优势与存在的问题,进而探究了铂系脱氢催化剂的失活原因。最后对铂系脱氢催化剂的研究前景做了展望,提出该系列催化剂的主要发展方向包括降低贵金属铂的负载量、提高催化剂的稳定性、减少积炭副反应等。     

Thermochemical conversion of polymer wastes into hydrocarbon fuels over various fluidizing cracking catalysts

A mixture of hospital post-commercial polymer waste (LDPE/HDPE/PP/PS) was pyrolyzed over various catalysts using a fluidized-bed reactor operating isothermally at ambient pressure. The yield of volatile hydrocarbons with zeolitic catalysts (ZSM-5 > MOR > USY) were higher than with non-zeolitic catalysts (MCM-41 > ASA). MCM-41 with large mesopores and ASA with weaker acid sites resulted in a highly olefinic product mixture with a wide carbon number distribution, whereas USY yielded a saturate-rich product mixture with a wide carbon number distribution and substantial coke levels. The systematic experiments discussed in this paper show that the use of various catalysts improves the yield of hydrocarbon products and provide better selectivity in the product distributions. A novel developed model based on kinetic and mechanistic considerations which take into account chemical reactions and catalyst deactivation for the catalytic degradation of commingled polymer waste has been investigated. This model represents the benefits of product selectivity for the chemical composition such as alkanes, alkenes, aromatics and coke in relation to the performance and the particle size selection of the catalyst used as well as the effect of the fluidizing gas and reaction temperature.