乙醇在Ni-ZnO-ZrO_2-YSZ阳极SOFC上的发电性能

为考察乙醇用于固体氧化物燃料电池的可行性,用柠檬酸溶胶-凝胶制备阳极催化材料Ni-ZnO-ZrO2,利用机械混合法制备Ni-ZnO-ZrO2-YSZ(Y2O3稳定的ZrO2)阳极。用涂覆法,在YSZ电解质上,制备了Ni-ZnO-ZrO2-YSZ/YSZ/LSM(La0.85Sr0.15MnO3)与Ni-YSZ/YSZ/LSM的单体电池。在不同蒸发器操作温度、电池操作温度和乙醇蒸气流量下,以乙醇为燃料进行发电实验,对两种阳极的电池发电性能进行比较。实验结束后,用SEM检测了两种电池阳极的表面。结果表明,Ni-ZnO-ZrO2-YSZ阳极SOFC的电池输出性能明显高于Ni-YSZ阳极,且Ni-ZnO-ZrO2-YSZ阳极具有较好的抗积炭能力。     

Effect of methane co-feeding on the selectivity of ethylene produced from oxidative dehydrogenation of ethane with CO2 over a Ni-La/SiO2 catalyst

A Ni-La/SiO₂ catalyst was prepared through the incipient wetness impregnation method and tested in the oxidative dehydrogenation of ethane (ODHE) with CO₂. The fresh and used catalysts were characterized by XRD and SEM techniques. The Ni-La/SiO₂ catalyst exhibited catalytic activity for the oxidative dehydrogenation of ethane, but with low ethylene selectivity in the absence of methane. The selectivity to ethylene increased with increasing molar ratio of methane in the feed. The carbon deposited on the catalyst surface in the sole ODHE with CO₂ was mainly inert carbon, while much more filamentous carbon was formed in the presence of methane. The filamentous carbon was easy to be removed by CO₂, which might play a role in improving the conversion of ethane to ethylene. The introduction of methane might affect the equilibrium of the CO₂ reforming of ethane and the ODHE with CO₂. As a consequence, the synthesis gas produced from CO₂ reforming of methane partly inhibited the reaction of ethane and promoted the ODHE with CO₂, thus increasing the selectivity of ethylene.     

In situ CO2 reactivation of FeCrOx/C catalyst in the oxidative dehydrogenation of ethane to ethylene

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乙醇在Ni-ZnO-ZrO2-YSZ阳极SOFC上的发电性能

为考察乙醇用于固体氧化物燃料电池的可行性,用柠檬酸溶胶 凝胶制备阳极催化材料Ni-ZnO-ZrO₂,利用机械混合法制备Ni-ZnO-ZrO₂-YSZ(Y₂O₃稳定的ZrO₂)阳极。用涂覆法,在YSZ电解质上,制备了Ni-ZnO-ZrO₂-YSZ/YSZ/LSM（La_0.85Sr_0.15MnO₃）与Ni-YSZ/YSZ/LSM的单体电池。在不同蒸发器操作温度、电池操作温度和乙醇蒸气流量下,以乙醇为燃料进行发电实验,对两种阳极的电池发电性能进行比较。实验结束后,用SEM检测了两种电池阳极的表面。结果表明,Ni-ZnO-ZrO₂-YSZ阳极SOFC的电池输出性能明显高于Ni-YSZ阳极,且Ni-ZnO-ZrO₂-YSZ阳极具有较好的抗积炭能力。     

Methane-fueled SOFC with traditional nickel-based anode by applying Ni/Al2O3 as a dual-functional layer

Novel γ-Al₂O₃ supported nickel (Ni/Al₂O₃) catalyst was developed as a functional layer for Ni–ScSZ cermet anode operating on methane fuel. Catalytic tests demonstrated Ni/Al₂O₃ had high and comparable activity to Ru–CeO₂ and much higher activity than the Ni–ScSZ cermet anode for partial oxidation, steam and CO₂ reforming of methane to syngas between 750 and 850 °C. By adopting Ni/Al₂O₃ as a catalyst layer, the fuel cell demonstrated a peak power density of 382 mW cm^?2 at 850 °C, more than two times that without the catalyst layer. The Ni/Al₂O₃ also functioned as a diffusion barrier layer to reduce the methane concentration within the anode; consequently, the operation stability was also greatly improved without coke deposition.     

Characteristic simulation with various anode support thicknesses of membrane electrode assembly in SOFC

This study focuses on the research of solid oxide fuel cell (SOFC) and proposes reasonably practical designs, analyses, and numerical analyses with coupling software in physics, COMSOL Multiphysics, as the analysis tool to discuss the effects on the SOFC performance. This research applies the design of electrode support (anode support) to substitute the original electrolyte support, Yttria-stabilized zirconia, so that the electrolyte membrane could form a membrane to reduce ohmic resistance and increase power density. This study further discusses the effects of various flow fields (counterflow and co-flow) on internal mass transfer and SOFC performance. The findings show that the cell performance of SOFC with co-flow is better than counterpart with counterflow under anode support thickness 1,000 μm. Regarding the analyses of porosity effect with the porosity 0.7 and tortuosity 4.5, the power density reaches the maximum that could enhance the cell performance.     

Tunable, light-assisted co-generation of CO and H2 from CO2 and H2O by Re(bipy-tbu)(CO)3Cl and p-Si in non-aqueous medium

The light-assisted co-generation of carbon monoxide and hydrogen from carbon dioxide and water is reported. The combination of a homogeneous CO-evolving electrocatalyst and a heterogeneous H(2)-evolving photoelectrode surface provides for tunability of the H(2)/CO ratio. A total Faradaic efficiency of 102 ± 5% and a H(2)/CO ratio of 2:1 were achieved at a low homogeneous catalyst concentration (0.5 mM) in acetonitrile/water mixtures.     

High performance cathode-supported SOFC with perovskite anode operating in weakly humidified hydrogen and methane

A high performance cathode-supported solid oxide fuel cell (SOFC), suitable for operating in weakly humidified hydrogen and methane, has been developed. The SOFC is essentially made up by a YSZ/LSM composite supporting cathode, a thin YSZ film electrolyte, and a GDC-impregnated La_0.75Sr_0.25Cr_0.5Mn_0.5O₃ (LSCM) anode. A gas tight thin YSZ film (∼27 μm) was formed during the co-sintering of cathode/electrolyte bi-layer at 1200 °C. The cathode-supported SOFC developed in this study showed encouraging performance with maximum power density of 0.182, 0.419, 0.628 and 0.818 W cm⁻² in air/3% H₂O–97% H₂ (and 0.06, 0.158, 0.221 and 0.352 W cm⁻² in air/3% H₂O–97% CH₄) at 750, 800, 850 and 900 °C, respectively. Such performance is close to that of the cathode-supported cell (0.42 W cm⁻² vs. 0.455 W cm⁻² in humidified H₂ at 800 °C) developed by Yamahara et al. [Solid State Ionics 176 (2005) 451–456] with a Co-infiltrated supporting LSM-YSZ cathode, a (Sc₂O₃)_0.1(Y₂O₃)_0.01(ZrO₂)_0.89 (SYSZ) electrolyte of 15 μm in thickness and a SYSZ/Ni anode, indicating that the performance of the GDC-impregnated LSCM anode is comparable to that made of Ni cermet while stable in weakly humidified methane fuel.     

Hydrogenation of CO2 conjugated with dehydrogenation of cyclohexane over an intermetallic catalyst

Transformations of carbon dioxide catalyzed by the hydride form of [TiFe_0.95Zr_0.03Mo_0.02]H_x, by the industrial Pt/Al₂O₃ catalyst, and by a mixture of the above materials were studied. Study of the thermal desorption of H₂ showed the presence of two forms of absorbed hydrogen, namely, the weakly bound hydrogen, which is evolved from the intermetallic structure on heating to 430 °C under Ar, and the strongly bound hydrogen (SBH), which remains in the intermetallic compound at higher temperatures (up to 700 °C). In a carbon dioxide medium, the SBH enters into selective CO₂ reduction to give CO at 350—430 °C and 10—12 atm. The selectivity of the formation of CO reaches 80—99% for conversion of CO₂ between 50—70%, the SBH being consumed almost entirely for the reduction of CO₂. In the presence of the mixed catalyst, conjugate reactions proceed efficiently; dehydrogenation of cyclohexane yields hydrogen, which is consumed for CO₂ hydrogenation.     

Experimental studies of immobilized-yeast,packed-bed reactors with reduced CO2 entrapment

A horizontal packed-bed reactor with baffles (HPBR) and a continuously stirred tank reactor with intermittent paddle agitation have been shown to considerably reduce the CO₂ entrapment when glucose is fermented with immobilized baker’s yeast in calcium alginate beads. Using high cell contents in the gel resulted in internal mass transfer hindrance. The highest productivity was obtained with the HPBR giving 29 g EtOH/Lh at an ethanol yield of 90%. The substrate used was 100 g/L glucose. Fermentation of lactose and deproteinized whey by coimmobilized baker’s yeast and |3-galactosidase resulted in much lower productivity-about 5 g EtOH/L.h because of the slow fermentation of galactose.     

High internal phase CO2-in-water emulsions stabilized with a branched nonionic hydrocarbon surfactant

A nonionic-methylated branched hydrocarbon surfactant, octa(ethylene glycol) 2,6,8-trimethyl-4-nonyl ether (5b-C12E8) emulsifies up to 90% CO2 in water with polyhedral cells smaller than 10 microm, as characterized by optical microscopy. The stability of these concentrated CO2/water (C/W) emulsions increases with pressure and in some cases exceeds 24 h. An increase in pressure weakens the attractive van der Waals interactions between the CO2 cells across water and raises the disjoining pressure. It also enhances the solution of the surfactant tail and drives the surfactant from water towards the water-CO2 interface, as characterized by the change in emulsion phase behavior and the decrease in interfacial tension (gamma) to 2.1 mN/m. As the surfactant adsorption increases, the greater tendency for ion adsorption is likely to increase the electrostatic repulsion in the thin lamellae and raise the disjoining pressure. As pressure increases, the increase in disjoining pressure and decrease in the capillary pressure (due to the decrease in gamma) each favor greater stability of the lamellae against rupture. The electrical conductivity is predicted successfully as a function of Bruggeman's model for concentrated emulsions. Significant differences in the stability are observed for concentrated C/W emulsions at elevated pressure versus air/W or C/W foams at atmospheric pressure.     

Determination of H2S and HCl concentration limits in the fuel for anode supported SOFC operation

Solid oxide fuel cell (SOFC) is an electric generator, operating based on electrochemical reaction converting gaseous fuel to electricity and heat. It is characterized by the high electrical efficiency of up to 70% with cogeneration and negligible emission of pollutants. Syngas from the biomass gasification is considered to be a possible fuel for solid oxide fuel cell systems. However, high level of contaminants such as H₂S, HCl, alkali metals, tars and particulates, in addition to possibility of carbon deposition and high temperature gradients due to internal reforming of hydrocarbons requires cleaning and conditioning of the syngas stream. The current status of the effect of contaminants on the SOFC performance has been reviewed and effects of single contaminants (H₂S, HCl) has been tested. It has been found that anode supported solid oxide fuel cell (AS-SOFC) with Ni/YSZ cermet anode can tolerate up to 1 ppm H₂S and up to 10 ppm HCl without significant performance degradation.      

Vibrational mode and collision energy effects on reaction of H2CO+ with CO2

The effects of collision energy (Ecol) and five different modes of H2CO+ vibration on the title reaction have been studied over the center-of-mass Ecol range from 0.1 to 3.2 eV, including measurements of product ion recoil velocity distributions. Electronic structure and Rice-Ramsperger-Kassel-Marcus calculations were used to examine properties of various complexes and transition states that might be important along the reaction coordinate. Two product channels are observed, corresponding to Hydrogen Transfer (HT) and Proton Transfer (PT). Both channels are endothermic with similar onset energies of approximately 0.9 eV; however, HT dominates over the entire Ecol range and accounts for 70-85% of the total reaction cross section. Both HT and PT occur by direct mechanisms over the entire Ecol range, and have similar dependence on reactant vibrational and collision energy. Despite these similarities, and the fact that the two channels are nearly isoenergetic and differ only in which product moiety carries the charge, their dynamics appear quite different. PT occurs primarily in large impact parameter stripping collisions, where most of the available energy is partitioned to product recoil. HT, in contrast, results in internally hot products with little recoil energy and a more forward-backward symmetric product velocity distribution. Vibration is found to affect the reaction differently in different collision energy regimes. The appearance thresholds are found to depend only on total energy, i.e., all modes of vibration are equivalent to Ecol. With increasing Ecol, vibrational energy becomes increasingly effective, relative to Ecol, at driving reaction. For HT, this transition occurs just above threshold, while for PT it begins at roughly twice the threshold energy.     

Theoretical investigation of the "CO in"-"CO out" isomerization in a [2Fe-2S] ferredoxin: free energy profiles and redox states

This paper reports on extensive molecular dynamics simulations (about 40 ns in total) in both the reduced and the oxidized states of Ferredoxin from Cyanobacterium Anabaena PCC7119. These calculations have provided us with the free energy profile of the phi(47) backbone angle which controls the "CO in" to "CO out" transition of Cys46 in the reduced and oxidized Fd7119. Our main motivation has been to identify the time scales involved in the reduction of Fd and single out the amino acid residues crucially affecting the conformational change and, thus, electron transfer. The free energy profiles obtained in this study are relevant to electron transfers in the PSI/Fd7119 and Fd7119/FNR complexes. Our findings based on hydrated ferredoxin simulations are that activated processes are to occur in the protein during electron transfer to and from ferredoxin. The relative stability and the activation barrier of the "CO in" to "CO out" transition can be modulated by the distance between the Ser47 and the Glu94 residues. In our calculations, for short distances, the "CO in" state is favored in the reduced form, whereas for large distances, the "CO out" state becomes increasingly favored. Accordingly, conformational changes in Fd7119 when bound to PSI or FNR can have crucial effects on the kinetics of the electron transfer. Our simulations also show that the hydrogen bond between between Ser47(OG) and Cys46(O) is essential to lock in the "CO out" state. This finding explains why only the Ser47Thr Fd7119 mutant sustains electron transfer activity, as only residues serine and threonine can form a specific hydrogen bond with Cys46(O). Finally, our simulations predict that Phe65 has a large probability of being in close contact with the Cys46(O) at the top of the conformational free energy barrier. This carbonyl/phenyl ring interaction can then facilitate the de-localization of the Fd's electron toward the Pi orbitals of Phe65 aromatic ring which is thought to be crucial to the Fd7119/FNR electron transfer     

Oxidative dehydrogenation of ethylbenzene to styrene with CO2 over Al-MCM-41-supported vanadia catalysts

Catalytic performance of Al-MCM-41-supported vanadia catalysts (V/Al-MCM-41) with different V loading was investigated for oxidative dehydrogenation of ethylbenzene to styrene (ST) with CO₂ (CO₂-ODEB). For comparison, pure silica MCM-41 was also used as support for vanadia catalyst. The catalysts were characterized by N₂ adsorption, X-ray diffraction (XRD) pyridine-Fourier-transform infrared spectroscopy, H₂-temperature-programmed reduction, thermogravimetric analysis (TGA), UV-Raman, and diffuse reflectance (DR) UV–vis spectroscopy. The results indicate that the catalytic behavior and the nature of V species depend strongly on the V loading and the support properties. Compared with the MCM-41-supported catalyst, the Al-MCM-41-supported vanadia catalyst exhibits much higher catalytic activity and stability along with a high ST selectivity (>98%). The superior catalytic performance of the present V/Al-MCM-41 catalyst can be attributed to the Al-MCM-41 support being more favorable for the high dispersion of V species and the stabilization of active V⁵⁺ species. Together with the characterization results of XRD, TGA, and DR UV–Vis spectroscopy, the deep reduction of V⁵⁺ into V³⁺ during CO₂-ODEB is the main reason for the deactivation of the supported vanadia catalyst, while the coke deposition has a less important impact on the catalyst stability.     

亚微米ZSM-5负载Cr催化剂上乙烷CO2气氛下脱氢制乙烯

石油资源的日趋短缺使天然气和页岩气的开发利用受到重视,因而低碳烷烃脱氢制取低碳烯烃也随之引起了人们越来越多的关注.由于乙烷纯脱氢反应的平衡收率低,能耗高,而氧气氧化脱氢又易将乙烷深度氧化为CO2或CO,因此开发具有反应条件温和、装置投资和操作费用低等优势的CO2气氛下乙烷脱氢的技术路线日益得到重视. CrOx是该反应理想的催化剂之一, CO2的加入可使CrOx对乙烷脱氢的催化活性提升3倍,然而受困于CrOx过小的比表面积,通常将CrOx制备成负载型催化剂使用. CrOx的常见载体有Al2O3, ZrO2和SiO2等氧化物及MCM-41, SBA-15, SBA-1和MSU-x等介孔硅材料, ZSM-5作为载体负载CrOx用于低碳烷烃脱氢的研究则较少,所得结果也不甚理想.我们采用亚微米尺寸的ZSM-5作为载体制备了负载型CrOx催化剂,研究了其在CO2气氛下催化乙烷脱氢反应,发现该催化剂具有非常优异的脱氢活性,高硅铝比和Na型的ZSM-5作载体对反应更加有利,而且在反应进行50 h后,催化剂依然保持很好的活性和很高的乙烯收率,这是在一般负载型CrOx催化剂上所不能实现的.
　　X射线光电子能谱(XPS)表征发现, Na型ZSM-5载体制得的催化剂具有更高的Cr6+/Cr3+比.一般认为, Cr6+是Cr系催化剂进行低碳烷烃脱氢反应时的活性位(或活性位前驱体),因此可以初步判定, Na型载体具有很好催化效果的原因可能是由它制得的催化剂具有更多的反应活性位.程序升温还原(H2-TPR)表征结果证实了这一点, Na型载体明显具有更高的H2消耗量;也就是说, Na型载体制得的催化剂具有更多的可还原Cr物种,即脱氢活性位.进一步表征发现,反应活性还与Cr物种存在形式有关.文献报道,低聚态的Cr物种和孤立态的Cr物种比Cr2O3有更好的催化活性.通过漫反射紫外-可见光谱(UV-Vis)对Cr物种的存在形态进行表征后发现, Na型载体上Cr主要以四配位形式存在,而在H型载体上出现了对应于六配位的Cr物种;激光Raman表征结果表明, Na型载体上出现的都是低聚态Cr物种和孤立态Cr物种,而H型载体上出现了明显的对应于α-Cr2O3的峰,说明相较于H型载体, Na型载体更有利于Cr组分分散,这也是Na型ZSM-5载体催化剂具有更高活性的原因之一.
　　CO2引入后对乙烷脱氢反应具有明显的促进作用,特别是在CO2/C2H6=5时,催化剂上C2H6转化率是非CO2气氛下的3.2倍;同时, CO2的引入也提高了脱氢反应的稳定性.在非CO2气氛下,反应进行6 h后, C2H6转化率降低到初活性的60%左右,而在CO2/C2H6=5时,相同时间内催化剂活性下降仅有5%左右.实验分析了CO2对脱氢反应具有促进作用的原因.在脱氢反应温度650 oC下, CO2/H2=1时进行了逆水煤气反应测试,发现CO2的转化率达到22.5%,说明引入CO2后可以通过逆水煤气反应有效地消耗掉乙烷脱氢反应生成的H2,从而促进反应向脱氢方向进行; CO2的引入也可以促进Cr物种的CrOx/CrOx-1循环,从而提高催化剂效率,减缓催化剂失活; CO2还可与反应中生成的积碳类物质发生Boudouard反应,将反应活性位暴露出来,从而提高催化剂的稳定性. CO2气氛下反应6 h后催化剂的积碳量为3.0%,低于非CO2气氛下的3.4%,同时在脱氢反应中生成的CO量与消耗掉的CO2量的比值约为1.4,也有力地说明Boudouard反应的存在.     

Study of oxidative dehydrogenation of ethylbenzene with CO2 on supported CeO2-Fe2O3 binary oxides

Nano-sheets Al₂O₃ supported CeO₂-Fe₂O₃ binary oxides were prepared by the vacuum impregnation method. The structural and textural properties were characterized by pertinent techniques, and the materials were evaluated as catalysts for the oxidative dehydrogenation of ethylbenzene with carbon dioxide (CO₂-ODEB). The characterization results show that all samples maintain the hierarchical structure, and CeO₂-like and Fe₂O₃-like solid solutions were formed when changing the Ce-to-Fe molar ratio. The catalytic performances indicate that CeO₂-Fe₂O₃ binary oxides were effective for CO₂-ODEB, and the activity is determined by mobile oxygen, which can facilitate the dehydrogenation process. The DFT studies further identified the reaction pathway and rate-determining step. The inter-transmission of oxygen species and the presence of CO₂ refill the oxygen vacancies and restore the redox cycle of CeO₂-Fe₂O₃ binary oxides.     

Tandem electrocatalytic CO2 reduction with Fe-porphyrins and Cu nanocubes enhances ethylene production

Copper-based tandem schemes have emerged as promising strategies to promote the formation of multi-carbon products in the electrocatalytic CO₂ reduction reaction. In such approaches, the CO-generating component of the tandem catalyst increases the local concentration of CO and thereby enhances the intrinsic carbon–carbon (C–C) coupling on copper. However, the optimal characteristics of the CO-generating catalyst for maximizing the C₂ production are currently unknown. In this work, we developed tunable tandem catalysts comprising iron porphyrin (Fe-Por), as the CO-generating component, and Cu nanocubes (Cucub) to understand how the turnover frequency for CO (TOF_CO) of the molecular catalysts impacts the C–C coupling on the Cu surface. First, we tuned the TOF_CO of the Fe-Por by varying the number of orbitals involved in the π-system. Then, we coupled these molecular catalysts with the Cu_cub and assessed the current densities and faradaic efficiencies. We discovered that all of the designed Fe-Por boost ethylene production. The most efficient Cu_cub/Fe-Por tandem catalyst was the one including the Fe-Por with the highest TOF_CO and exhibited a nearly 22-fold increase in the ethylene selectivity and 100 mV positive shift of the onset potential with respect to the pristine Cu_cub. These results reveal that coupling the TOF_CO tunability of molecular catalysts with copper nanocatalysts opens up new possibilities towards the development of Cu-based catalysts with enhanced selectivity for multi-carbon product generation at low overpotential.

Coupling the tunability of molecular catalysts and copper nanocatalysts opens up new possibilities towards the development of Cu-based catalysts with enhanced selectivity for multi-carbon product generation at low overpotential.     

Intermolecular interaction between CO or CO2 and ethylene oxide or ethylene sulfide in a complex, investigated by Fourier transform microwave spectroscopy and ab initio calculations

The rotational spectra of the CO-ethylene oxide (EO), CO-ethylene sulfide (ES), CO(2)-EO, and CO(2)-ES complexes were measured by Fourier transform microwave spectroscopy in the frequency region from 4 up to 31 GHz. The isotopologues with a single (13)C atom in the EO or ES, (18)O in the EO, (34)S in the ES, and (13)C in the CO(2) moiety, respectively, were observed in natural abundance, and enriched samples, (13)CO or C(18)O in the CO-EO or CO-ES complex and C(18)OO and C(18)O(2) in the CO(2)-EO or CO(2)-ES complex, were employed to record respective rotational transitions. The rotational spectra observed for the CO-EO, CO-ES, CO(2)-EO, and CO(2)-ES complexes were analyzed by using an asymmetric-rotor S-reduced Hamiltonian to determine rotational and centrifugal distortion constants. The r(s) coordinates of the atoms in the four complexes, which were calculated from the observed rotational constants, led to a structure in which the CO or CO(2) moiety is located in a plane perpendicular to the EO or ES skeletal plane and bisecting the COC or CSC angle. We have also carried out ab initio molecular orbital calculations at the level of MP2 with basis sets 6-311++G(d,p) and aug-cc-pVDZ using the Gaussian 09 package. The MP2/6-311++G(d,p) calculations yield rotational constants in better agreement with the experimental values than with the other basis set; in other words, the molecular structures calculated using this basis set are close to those experimentally found for the ground state. The estimated dissociation energies of the complexes, including the zero-point vibrational energy corrections ΔZPV and the basis set superposition errors (BSSE) calculated with the counterpoise correction (CP), are in good agreement with the experimentally obtained binding energies E(B). We have applied an NBO analysis to the complexes to calculate the stabilization energy CT (=ΔE(σσ*)), which we found are closely correlated with the binding energies E(B). We have thus achieved a consistent overview on the intermolecular interaction in the complexes under consideration. It is to be noted that the spectral intensities of the inner OC(18)O-EO and OC(18)O-ES complexes were larger by a factor of 2 than those of the outer (18)OCO-EO/ES complexes. This observation was explained by the zero-point energy of the inner conformer being a little smaller than that of the outer one.