Precious Metal Catalysts Supported on Ceramic and Metal Monolithic Structures for the Hydrogen Economy

In a typical temperature-programmed desorption (TPD) experiment on a supported metal catalyst, a small amount of catalyst (10–200 mg) is contained in a reactor that can be heated by a furnace. An inert gas, usually helium at atmospheric pressure, flows over the catalyst. Following pretreatment to obtain a reduced catalyst, a gas is adsorbed on the surface, usually by pulse injections of the adsorbate into the carrier gas upstream from the reactor. After the excess gas is flushed out, the catalyst is heated to create a linear rise in temperature with time. A small thermocouple inserted in the catalyst measures the temperature and a detector downstream measures the change in the inert gas stream. The ideal detector is a mass spectrometer which measures the composition of the effluent stream as a function of catalyst temperature. Because of the high carrier-gas flow rate, the detector response is proportional to the rate of desorption if diffusion and readsorption are not limiting.     

Temperature-Programmed Desorption and Reaction: Applications to Supported Catalysts

In a typical temperature-programmed desorption (TPD) experiment on a supported metal catalyst, a small amount of catalyst (10-200 mg) is contained in a reactor that can be heated by a furnace. An inert gas, usually helium at atmospheric pressure, flows over the catalyst. Following pretreatment to obtain a reduced catalyst, a gas is adsorbed on the surface, usually by pulse injections of the adsorbate into the carrier gas upstream from the reactor. After the excess gas is flushed out, the catalyst is heated to create a linear rise in temperature with time. A small thermocouple inserted in the catalyst measures the temperature and a detector downstream measures the change in the inert gas stream. The ideal detector is a mass spectrometer which measures the composition of the effluent stream as a function of catalyst temperature. Because of the high carrier-gas flow rate, the detector response is proportional to the rate of desorption if diffusion and readsorption are not limiting.     

活性炭变压吸附回收环氧乙烷装置排放气中的乙烯

以活性炭为吸附剂，对工业环氧乙烷装置排放气中乙烯的回收进行了研究。测定了环氧乙烷装置排放气中主要组分的吸附等温线及脱附性能，发现活性炭对乙烯的吸附量较高，与氧气、氮气和氩气等组分的分离度较大。在此基础上，研究了活性炭的变压吸附性能，在常规真空脱附工艺条件下，乙烯的回收率较低，但通过提高脱附真空度或进行甲烷反向吹扫，可以大大提高乙烯回收率和惰性气体的脱附率。     

Characterization of catalysts for methane-coupling by means of temperature programmed desorption

The technique of temperature programmed desorption has been employed to study the adsorptive behaviour of CaO and Na₂O/CaO towards the reactants and products of the methane-coupling reaction. Two forms of adsorbed O₂ can exist on CaO, and they desorb at intermediate temperatures: the first corresponds to the sites for adsorption and desorption without reaction of CH₄, while the second to sites for desorption with total oxidation of CH₄ itself. At the temperatures of the activity runs for methane coupling (750–800 °C), no adsorbed species is therefore stable on the surface of CaO. 7% Na₂O/CaO shows different features, because the desorption of O₂ produces only a large broad peak at very high temperatures, corresponding to sites for adsorption and desorption with total oxidation of CH₄. (On the other hand a desorption peak of CH₄ at intermediates temperatures is also present, which seems to be due to a species, adsorbed undissociatively and desorbed without reaction). At the temperatures of the activity experiments, adsorbed species are therefore stable on the surface of Na₂O/CaO. A conclusion is therefore drawn on the necessity for the intervention of the gas phase O₂ during the methane coupling reaction in order to produce C₂-hydrocarbons, and on the greater importance of the surface reactions in the presence of Na₂O, in comparison to the case of CaO.     

Effects of matrix moisture on gas diffusion and flow in coal

Gas production from coal is a complex process whereby gas, initially adsorbed in the coal matrix, desorbs and diffuses through the matrix into the cleat and eventually flows through the cleat system into a production well or a drainage borehole. Hence, the gas production rate is mainly controlled by the gas diffusivity in the matrix and gas permeability in the cleat system. Moisture in the coal matrix has significant impact on gas adsorption capacity and would also play a key role in desorption and migration of gas. However, how moisture affects gas desorption and diffusion in the coal matrix is still poorly understood. In this work, experimental study is performed to investigate effects of moisture on gas sorption rate for an Australian coal. Coal seam gases, CH₄ and CO₂, are used in the study. The experimental results show that moisture content in the matrix has significant impact on the gas sorption rate and the impact of moisture content on the diffusion rate is stronger for CH₄ than CO₂. Moreover, the impact of moisture on gas diffusivity in pores with different size is different, suggested from the modelling results using the bidisperse approach. Furthermore, moisture in coal matrix would cause coal swelling/shrinkage and mechanical properties change that could impact on coal permeability under reservoir conditions. Experimental measurements of coal matrix swelling and Young’s modulus on the same coal sample show that matrix moisture content has significant impact on those properties and may have significant implications on coalbed methane recovery and CO₂ storage in coal.     

瞬变应答法研究苯催化氧化的反应机理

采用瞬变应答法研究了苯在钒催化剂上催化氧化的反应机理。通过对应答曲线的分析,证明氧首先被催化剂表面吸附,然后以较慢的速率转化为晶格氧,这一步是苯催化氧反应速率的控制步骤。吸附氧是生成 CO 和 CO_2的氧源;晶格氧是生成顺酐的氧源。气相苯不直接参与反应,但以较快的速率可逆吸附于催化剂上,吸附的苯与晶格氧反应生成中间物 IN,IN 进一步氧化生成顺酐。顺酐可逆吸附于催化剂上,其介吸速率较慢。中间物和吸附的顺酐对反应起阻滞作用。     

Adsorption and Activity of Proteins onto Mesoporous Silica

The adsorption and activity of cytochrome c onto two different MCM-41 materials, MCM-41/28 and MCM-41/45 with average pore diameters of 28 and 45 Å respectively, is presented. Nitrogen gas adsorption/desorption isotherms before and after protein adsorption, and peroxidative activity profiles of the adsorbed protein demonstrate that the protein is adsorbed into the mesoporosity and remains active. The adsorption of a range of different proteins onto both MCM-41/28 and 45 shows how protein properties affect adsorption.     

Benzyl coupling on bismuth-modified Pt(111)

It has been found that adsorbed benzyl (Ø-CH₂(a)), produced from methylcyclohexane, can undergo dimerisation to adsorbed bibenzyl (Ø-CH₂-CH₂-Ø) on a bismuth-modified Pt(111) surface. In this case, the bismuth was postdosed to the benzyl adlayer, as in bismuth postdosing thermal desorption mass spectroscopy (BPTDS). The bibenzyl product desorbs to give bibenzyl gas in good yield with respect to the starting benzyl or the reacted methylcyclohexane. This reaction competes poorly with simple hydrogenation of the benzyl species to toluene when adsorbed hydrogen is also present on the bismuth-dosed surface. In the absence of hydrogen, dimerization dominates the chemistry of this intermediate, although some direct desorption of benzyl radical also occurs. The dependence of the activation energy for benzyl coupling on the thickness of the bismuth film suggests that the bismuth resides between the Pt surface and the benzyl adlayer. Benzyl coupling and desorption occurs on Bi/Pt, whereas only its decomposition occurs on clean Pt. This is attributed to two effects: the weakness of C-Bi bond leads to a low barrier for benzyl coupling or desorption; and, (2) bismuth blocks Pt sites needed to stabilize the fragments of decomposition. Both D₂-BPTDS and this bismuth-induced coupling reaction in simple BPTDS were used to monitor the coverage of benzyl during its thermal decomposition on bismuth-free Pt(111), and the temperature dependence of the rate of its decomposition. Estimates of the bismuth-carbon bond strengths are also presented.     

含气页岩中水分赋存与分布的研究进展

页岩气（主要组分为甲烷,CH₄）作为一种新兴的非常规天然气,对于优化我国现行能源消费结构、缓解能源消耗过程中的环境污染问题具有重要意义。研究表明,含气页岩储层中页岩气主要以吸附态形式存在。影响含气页岩吸附性能的因素包括页岩自身理化性质和外部储层条件。其中,页岩中的水分是影响页岩气吸附/解吸的重要因素。因此,本文结合国内外相关研究工作,分析了含气页岩中水分的赋存与分布特征,归纳了页岩储层中水分的分析方法,指出了水分赋存与分布的后续研究方向。分析表明：①页岩中水分主要赋存于孔隙结构中,且无机孔隙中的水分赋存量比有机孔隙多;②水分子主要通过氢键吸附于有机孔隙的亲水性位点,以及经由氢键和表面作用力结合于黏土颗粒或孔隙表面;③水分含量与页岩黏土矿物含量及总有机碳（TOC）含量有关;④探明页岩中水分赋存与分布的实验表征手段包括水蒸气等温吸附、低温差示扫描量热、低场核磁共振、红外热成像和等离子体低温灰化等。虽然页岩中水分的研究已经引起国内外学者的关注,但是相比煤中水分的研究仍显不足。因此,本文指出后续需开展以下工作：探明水分在页岩中的无机矿物质空间和有机质空间的含量分布和空间分布特征;明确水分对页岩吸附/解吸CH₄流体的作用规律;联用实验科学和理论模拟方法,探明水分对页岩吸附/解吸CH₄流体的作用机理。     

An infrared spectroscopic study of the mechanism of chloromethane conversion to higher hydrocarbons on HZSM5 catalyst

Investigation of the reaction mechanism of chloromethane on ZSM5 is a new topic. In this work an in situ FTIR technique was employed to study the conversion processes of chloromethane, the active sites on HZSM5, and the desorption state of surface species. The catalytic conversion of chloromethane to higher hydrocarbons was also studied. It is demonstrated that chloromethane can be reversibly adsorbed on acidic sites of HZSM5 at room temperature. At 100°C chloromethane is irreversibly and dissociatively adsorbed on the strong acidic sites of HZSM5, on which surface methoxyl is formed as proved by infrared characteristic C-H stretchings of-CH₃ at 2960 and 2870 cm^–1. Alkoxyls are produced and adsorbed on the catalyst surface as characterized by the infrared absorption bands of -CH₂-groups at 1460 and 2930 cm^–1. At 100°C the adsorbed methoxyl and alkoxyls are the main surface species, and a small amount of aromatics might exist as detected by a characteristic absorption band at 1510 cm^–1. Between 100 and 200°C the adsorbed surface methoxyl and alkoxyls are converted to aromatics, and the occupied OH groups partially appear. At temperature higher than 300°C the adsorbed aromatics are thermally desorbed into the gas phase. Aromatics and alkanes are the main products in catalytic conversion. These results reveal that the formation of aromatics from methoxyl and alkoxyls is easier than the desorption of aromatics from HZSM5 catalyst. An alkoxyl mechanism is proposed for the conversion of chloromethane on HZSM5 based upon the experimental results and the three assumptions: (a) The primary C-C bond is formed from surface methoxyl groups via the methoxyl group polarization and C-H bond weakening, (b) The adsorbed alkoxyls are converted to aromatics via hydrogen transfer and bond rearrangement similar to the conventional carbenium ion mechanism for the aromatization of olefins and alkanes on HZSM5. The hydrogen atoms from the aromatization stimulate the desorption of alkoxyls to alkanes. (c) At temperature higher than 300°C surface reactions and desorption of adsorbed species take place simultaneously, determining the product distribution in the catalytic conversion.     

Adsorption and reaction of NO on activated carbon in the presence of oxygen and water vapour

A study of the adsorption and reaction of NO in the presence of oxygen and water vapour on an activated carbon obtained from oil palm shells is presented. The study is based on the measurement of breakthrough curves, at temperatures between 100 and 150 °C, and on the subsequent thermal desorption in a fix bed reactor. The concentration of the gas components, NO, O₂ and H₂O, corresponds to a simulation of a flue gas in a coal fired power plant. The experimental results show that the reactions on this system include the simultaneously adsorption, reduction and catalytic oxidation of NO together with the adsorption of created NO₂. During desorption NO₂ reacts to NO through a reductive desorption process. An acceleration of the NO oxidation occurs when the saturation level of the adsorbed NO is reached, resulting in a maximum on the breakthrough curve. Different adsorbed NO species are formed during the process: one thermal unstable NO, and three thermal stable NO species, NO₂, NO and (NO)₂ dimers, respectively.     

ANALYSIS OF TEMPERATURE-PROGRAMMED DESORPTION FROM POROUS CATALYSTS IN A FLOW SYSTEM

A comparison is reported between experimental and simulation results obtained from temperature-programmed desorption (TPD) spectra for H₂ and CO from Ni/SiO₂ catalysts. The gas/solid system is selected as representative of these adsorbates interacting with a Group-VIII metal. Intraparticle concentration gadients can be minimized by using a bed of small porous catalyst particles perfused by a flow of carrier gas while under these conditions axial concentration gradients in the bed cannot be avoided.

Previous models providing design criteria for analysis of TPD curves predict these conclusions, yet are overly restrictive. When allowance is made for repulsive interactions between adsorbates, it is found that significant redistribution of the adsorbate within the bed occurs. This results in nearly uniform adsorbed concentration profiles which are obtained when experimental conditions are selected properly. Consequently, specific guidelines can be offered to guide the experimentalist and methods are thus proposed to obtain TPD curves which are indicative of the desorption kinetics of the adsorbate.     

Sulphur poisoning of nickel-based hot gas cleaning catalysts in synthetic gasification gas II. Chemisorption of hydrogen sulphide

The effect of different components of gasification gas on sulphur poisoning of nickel catalysts were studied. In addition, the sulphur distribution and content of nickel catalyst beds were analysed to account the poisoning effect of sulphur on the activity of catalysts to decompose tar, ammonia and methane. The desorption behaviour of chemisorbed sulphur from the bed materials was monitored by temperature programmed hydrogenation (TPH). It was established that bulk nickel sulphide was active in decomposing ammonia in high-temperature gasification gas-cleaning conditions. The decomposing activity of methane was not affected by bulk nickel sulphide formation, but that of toluene was decreased. The activity of the catalyst regained rapidly when H₂S was removed from the gas. However, the conversion of ammonia was not regained at as high a level as before sulphur addition, most probably due to irreversible sulphur adsorption on the catalyst. The temperature increase could also be used to regenerate the catalyst performance especially in respect to methane and toluene. Sulphur adsorbed on nickel catalysts in different chemical states depends on the process conditions applied. At >900°C the sulphur adsorbed on the catalyst formed an irreversible monolayer on the catalyst surfaces, while at <900°C the adsorbed sulphur, probably composed of polysulphides (multilayer sulphur), was desorbed from the catalyst in sulphur-free hydrogen containing atmosphere. However, a monolayer of sulphur still remained on the catalyst after desorption. The enhanced effect of high total pressure on sulphur-poisoning of nickel catalysts could be accounted for the increased amount of sulphur, probably as a mode of polysulphides, adsorbed on the catalyst.     

不同煤阶的原生煤、构造煤等量解吸焓的比较

煤阶不同，对瓦斯的控制作用亦不同。本文根据温度-压力-吸附方程将沁水盆地大宁煤矿的高阶原生煤、构造煤与平顶山五矿的中阶构造煤、原生煤这4种煤的系列等温吸附数据进行有效地转换，并由所得的温度-压力-吸附方程计算这些煤的吸附等量线。高中阶原生煤与构造煤的吸附等量线都证实：吸附是系统向环境放热，放热越多，则系统越稳定；解吸是系统从环境吸热，吸热越少，则系统越稳定。在吸附量都为15.0cm³/g时，高阶原生煤单位等量吸附所放的热为1.95kJ/(mol·cm³·g)，均高于其他3种煤，其必然最先吸附。在吸附量都为15.0cm³/g时，中阶构造煤单位等量解吸所吸的热为0.52kJ/(mol·cm³·g)，均低于其他3种煤，其必然最先解吸。建议将不同构造煤（碎裂煤、片状煤、碎斑煤、糜棱煤等）按照单位等量解吸所吸热量的大小进行解吸排序，可为煤及瓦斯突出研究提供热力学参考。     

The simultaneous adsorption of carbon dioxide and water vapour by fixed beds of molecular sieves

In an isothermal fixed bed absorption system for constant inlet flowrate of inert gas and concentrations of two adsorbates the more strongly adsorbed component will displace the weaker one and effect its breakthrough characteristics. A small scale technique was used to study this phenomenon for the adsorption of water vapour and carbon dioxide on 4A type synthetic zeolites with helium as the carrier gas. Single adsorbate equilibria and rate data determined with the binary mixtures were then used to calculate the results for the ternary one. Partial differential equations were derived to describe the mass transfer of each adsorbate based on pore diffusion in the adsorbent as a major rate controlling mechanism. With a simplified binary Langmuir equilibrium to describe the effect of water on the adsorption of carbon dioxide, and assuming that the effective pore diffusion coefficient of one adsorbate was not affected by the presence of the other, accurate predictions of the concentration transient were obtained. Four zones are formed in the bed with the ternary mixture resulting from the desorption of carbon dioxide by water, the concentrations of the former rising above the inlet value. An enhanced rate of adsorbed phase transport of water was found, additional to that expected from macropore diffusion, suggesting that surface or capillary flow of the adsorbate occurred.     

Role of promoters on Rh/SiO2 in CO hydrogenation: A comparison using DRIFTS

La, V, Zn, Cu, Fe, Li and Ag promoted Rh/SiO₂ catalysts were investigated for the synthesis of ethanol during CO hydrogenation at 230 °C and 1.8 atm. As is well known, the activity and selectivity depend heavily on the choice of promoter. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to probe the effects of La, V, Zn and Cu on CO adsorption and hydrogenation. From the IR study, it was found that the behavior of CO adsorbed on the differently promoted catalysts was very different. While La enhanced total CO adsorption, the addition of V, Zn and Cu suppressed CO adsorption to different extents. The doubly promoted Rh-La/V/SiO₂ showed only moderate CO adsorption. Results from DRIFTS suggest that the higher catalytic activity (compared to the non-promoted catalyst) observed for the La singly promoted Rh/SiO₂ catalyst may primarily be caused by an increase in the concentration of the adsorbed CO species in the presence of H₂, possibly due to the formation of new active sites at the LaO_x-Rh interface. The higher catalytic activity of the V singly promoted Rh/SiO₂ catalyst could be ascribed to an increased desorption rate/reactivity of the adsorbed CO species. The La and V doubly promoted catalyst showed both new adsorbed CO species and increased desorption rate/reactivity of the adsorbed species during CO hydrogenation due to a synergistic promoting effect of La and V. The addition of Zn or Cu promoters significantly reduced the desorption rate/reactivity of the adsorbed CO species on Rh/SiO₂, leading apparently to the much reduced activities for CO hydrogenation observed.     

Temperature and pressure dependence of molecular adsorption on single wall carbon nanotubes and the existence of an “adsorption/desorption pressure gap”

The interaction of acetone with single wall carbon nanotubes (SWCNTs) was studied by temperature programmed desorption with mass spectrometry (TPD-MS), after reflux, sonication, or exposure to 7.6 Torr of acetone vapors at room temperature. Acetone molecules adsorb strongly on SWCNTs desorbing at ∼400-900 K, corresponding to desorption energies of ∼100-225 kJ/mol, as intact molecules. Exchange of intact adsorbed molecules with gas phase species was observed in successive dosing of hydrogenated and deuterated acetone molecules. The desorption energies reported here are in stark contrast to the desorption energies (∼75 kJ/mol) reported earlier for SWCNTs interacting with acetone under high vacuum at cryogenic temperatures. This result suggests activated adsorption/desorption, and is also observed for adsorption of ethanol, methane, n-butane and 1,3-butadiene on SWCNTs and on carbon black. Quantum chemical calculations suggest that adsorption in interstitial channels of bundles formed of large-diameter SWCNTs is possible and can account for high desorption barriers, a result of strong dispersion interactions between neighboring SWCNTs.     

Enhanced selectivity and formation of ethylbenzene for acetophenone hydrogenation by adsorbed oxygen on Pd/SiO2

The effect of adsorbed oxygen for selectivity of acetophenone (AP) hydrogenation on Pd/SiO₂ catalyst at 298 K has been studied by means of gas phase acetophenone hydrogenation, infrared (IR) spectra, and temperature-programmed desorption. Acetophenone hydrogenation on reduced Pd/SiO₂ catalyst reveals a typical series reaction in which phenylethanol (PE) is the intermediate for ethylbenzene (EB) formation. The selectivity of the reaction is towards phenylethanol at low temperature. The oxidized Pd/SiO₂ catalyst exhibits very different catalytic selectivity with reduced catalyst. The selectivity of ethylbenzene can be significantly boosted to over 90%, even if the reaction approaches zero conversion, suggesting that phenylethanol needs not be an intermediate for production of ethylbenzene from acetophenone. The formation of ethylbenzene and phenylethanol on oxidized Pd may be controlled by a parallel reaction pathway. The numbers of adsorbed oxygen on Pd surface strongly dominate the rate of EB formation. The bulk Pd oxide cannot be reduced by hydrogen at 298 K, so the oxygen atoms in Pd bulk act a poison for AP hydrogenation, leading to deactivation of oxidized Pd catalyst. The adsorbed oxygen on Pd surface plays the important role that can activate the C---H bond of CH₃ group in acetophenone, leading to the formation of a new intermediate (perhaps acetophenone enolate). This intermediate is the key species that will be further hydrogenated to ethylbenzene.     

大孔树脂吸附分离酶解法苦楝素提取液的研究

研究了大孔树脂吸附分离酶解法苦楝素提取液的工艺条件及参数,LS-100型大孔吸附树脂明显优于AB-8型和NAK-Ⅱ型,其吸附分离苦楝素的吸附优化条件为:溶液pH值7.0,吸附温度45℃,平衡吸附时间4 h;解吸优化条件为:解吸剂为80%乙醇-水溶液,pH值5.0,解吸操作温度35℃,时间2.5 h。在此优化条件下,苦楝素的饱和吸附量可达201.6 mg/g,解吸率达88.9%。     

Pollutant adsorption during activated carbon and steam regeneration in technical columns (experiments, modelling): Part 2. Influence of process parameters during steam regeneration of activated carbon beds on pollutant exit concentration

Experiments in activated carbon columns of technical scale with upstream adsorption and downstream steam regeneration showed that pollutant exit concentration of waste gas can be markedly decreased if the upper zone of the fixed bed is preheated to 120 °C before desorption and, additionally, if the bed is desorbed with superheated steam with a temperature 150 °C. With this improved steam regeneration technique a decrease in pollutant exit concentration is achieved: for example, from 20 to 3 mg m⁻³ toluene. An increase in adsorption time before pollutant breakthrough from 12 to 19 h is also noted.

During regeneration of a cold bed of activated carbon with saturated steam the particles will become wetted with condensate outside and adsorbed steam inside. These water condensation/adsorption effects are markedly reduced by preheating the particles to temperatures so far above that of steam condensation that steam adsorption is prevented too. Additionally the regeneration steam is superheated so that the temperature drop caused by heat of pollutant desorption is not so great that steam adsorption occurs.

The whole desorption-adsorption cycle in a technical scale bed, including the effects of Steam condensation/ adsorption, flux and suction of condensate, hetero-azeotropic pollutant distillation and evaporation of condensate was modelled.

Radial maldistribution effects (discussed in part 1 of this paper, Chem. Eng. Proc., 32 (1993) 359) have not been taken into account here.

The calculated flux rates of pollutant in the gas mixture leaving the bed during desorption and the pollutant breakthrough curves at the following adsorption step correlate quite well with experimental results.