Adsorbed CO Molecules Research Articles

CFD Simulation of CO2 and Methane Adsorption at Various Temperature for MOF-5 using Dual-site and Single-site Langmuir Model

The annual increase in energy demand has led to an increase in greenhouse gas emissions, in particular CO2 emissions from the power generation industry. Carbon Capture and Utilization are technologies applied to capture CO2 gases and transform the gases into a different energy source. The adsorption technology to capture CO2 gases was chosen due to the minimum energy consumption and low costs required for an industrial application for sustainability. Metal-Organic Framework (MOF) has a reasonably high CO2 adsorption capability. It has been applied as an adsorbent for capturing and storing CO2. In this study, a comparison of CFD simulation with experimental CO2 and methane adsorption values in solid adsorbent beds containing MOF-5 at various temperatures was presented. The simulation was performed using 2D and 3D models from 0℃ at STP to 130℃ for CO2 and methane gas molecules. In addition, the isothermal and kinetic adsorption model was added to the simulations. This includes Single- and Dual-Site Langmuir adsorption isotherm and Linear Driving Force. The porous media model was then activated to imitate packed bed adsorbent and measured the pressure drop from the simulation. The results showed that the CO2 adsorption values of MOF-5 decrease as the adsorbent temperature increases. There was a decline of 0.002 mmol/g of adsorbed CO2 molecules per 10-kelvin difference. The CO2 adsorption value was 0.53 mmol/g at STP and 1.15 mmol/g for CH4 at STP. Both CO2 and CH4 adsorption were used to suggest optimal CO2 adsorption for the Pressure Swing Adsorption cycle.

The Effect of Different Promoters (La2O3, CeO2, and ZrO2) on the Catalytic Activity of the Modified Vermiculite-Based Bimetallic NiCu/EXVTM-SiO2 Catalyst in Methane Dry Reforming.

An X-NiCu/EXVTM-SiO2 (X = La, Ce, and Zr) catalyst was successfully prepared by using modified vermiculite as a support by the impregnation method. This experiment investigated the effects of La2O3, CeO2, and ZrO2 promoters on the activity of the NiCu/EXVTM-SiO2 catalyst. The study found that the addition of three different metal oxides did not improve the activity of the NiCu/EXVTM-SiO2 catalyst. On the contrary, some Ni active sites were covered by the promoter, which reduced the number of active sites, resulting in its catalytic activity lower than NiCu/EXVTM-SiO2. In addition, the promoted catalysts that were repeatedly calcined two times can significantly reduce the textural property as well as active sites of the catalyst, resulting in the lower activity. However, in X-NiCu/EXVTM-SiO2, Ce-NiCu/EXVTM-SiO2 showed relatively high initial catalytic activity, with the initial conversion rate of CH4 reaching 60.1% and the initial conversion rate of CO2 reaching 89.1%. This is mainly because the catalyst has a stronger basic site on the surface to facilitate the adsorption of CO2 molecules, and the smaller metal particle size is also conducive to the cleavage of C–H bonds.

Surface-amino-induced boosting solar conversion of CO2 to CO over natural metal-free catalyst

Design and construction of visible-light-responsive and low-cost catalyst to improve photocatalytic CO2 reduction efficiency are highly urgent due to rapid increment of CO2 emission. Herein, a facile but effective strategy is proposed to synthesize heteroatoms-doped porous treated rape pollen (TRP) and NH2-functionalized TRP for CO2 reduction. Heteroatoms doping can accelerate photoinduced charge transfer between neighboring carbon atom. The introduction of NH2- group offers effective sites to boost CO2 adsorption, which is beneficial to facilitate CO2-to-CO conversion. The experimental results indicate that TRP-NH2 exhibits visible-light-driven CO formation rate of 1165.3 μmol h−1 g−1 in the gas-solid reaction system without co-catalysts or sacrificial agents, which is 2.4 and 70.1 times than those of TRP (488.4 μmol h-1 g-1) and g-C3N4 (16.6 μmol h-1 g-1), and exceeds reported state-of-the-art carbon-based photocatalysts. The theoretical investigation shows that the incorporation of NH2- group can improve its charge density and converge more electrons to adsorb CO2 molecules. In situ Fourier transform infrared (FT-IR) spectroscopy spectra disclose that the COOH* radical is the main intermediate. The findings reveal the correlation between surface NH2- group and photocatalytic CO2 reduction performance and can be extended to other sustainable metal-free based catalysts for solar-driven CO2 reduction.

Full solar spectrum driven plasmonic-assisted efficient photocatalytic CO2 reduction to ethanol

Photocatalytic carbon dioxide (CO2) reduction to valuable chemicals (ethanol) is an ideal way to realize artificial photosynthesis. It is still extremely difficult to achieve the challenge for photocatalytic CO2 reduction to multi-electronic products (C2H5OH). Here, we design the SrTiO3 (La Cr)/Cu @ Ni/TiN (STO/Cu @ Ni/TiN) to realize the high efficiency of photocatalytic CO2 reduction conversion into ethanol in the absence of sacrificial reagents. Furthermore, we use non-noble metallic materials such as Cu, Ni, and TiN to enhance the plasmonic effect for efficiently capturing solar full-spectrum energy instead of noble metals. Meanwhile, the TPD results show that Cu@Ni nanoparticles can enhance the chemical adsorption of CO2 molecules. STO/Cu @ Ni/TiN exhibit an optimal ethanol evolution rate of 21.3 μmol/(h·gcat.) and the ethanol selectivity of 79%, which is the highest value for photocatalytic CO2 reduction to ethanol, among the best values of our knowledge. Furthermore, the pathway of ethanol is confirmed by density functional theory (DFT) calculations and the 13C isotope experiment.

A recyclable CoGa intermetallic compound catalyst for the hydroformylation reaction

Metal leaching is an important obstacle for the development of CO-containing heterogeneous catalysis systems. The modulation of the metal surface could substantially influence the structural stability under a CO atmosphere. In this work, the inductively coupled plasma (ICP) results indicate that the leaching amount of cobalt in the CoGa intermetallic compound (CoGa IMC/SiO2) catalyst is notably less than that of the Co/SiO2 catalyst in hydroformylation reaction. The in situ Fourier Transform Infrared Spectroscopy (FTIR) results prove that aldehydes can be generated on CoGa IMC/SiO2 by heterogeneous hydroformylation reaction without the formation of Co carbonyl species. Moreover, the analysis of metal bond interaction proves that although the Co-Ga bond has a weaker metal interaction strength in the bulk phase, it has higher structural stability than the Co-Co bond with the adsorption of CO molecules. Above all, this work provides a strategy to suppress metal leaching for heterogeneous catalysis.

Theoretically predicted CO adsorption and dissociation on Ru-doped Co(1 0 0) surfaces

CO adsorption and dissociation on Ru-doped Co(100) surfaces at different CO coverage compared to clean surface were investigated based on spin-polarized density functional theory (DFT), in order to explore the effect of the initial step of Ru promoter on CO activation in cobalt-based Fischer-Tropsch synthesis (FTS). The results show that CO adsorption is highly site-dependent, the adsorption strength of CO at different types of adsorption sites is determined by the interaction between the adsorbed CO molecule and Ru-doped Co(100) surfaces. CO dissociation is promoted at hollow sites but inhibited at top and bridge sites above the Ru atoms. In addition, the amount of saturated adsorbed CO is increased while the amount of dissociated CO is decreased on the Ru-doped Co(100) surfaces at high coverage. Combining the experimental results, it is concluded that the adsorption model is preferred than substitution model for CO activation, because the increased CO molecular states in adsorption model is facile for the subsequent H-assisted dissociation on Co surface. The present work suggests that the addition of Ru promoter can improve the CO activation on Co(100) surface and pave the way for experimental research.

Enhancement of hydrogen production using Ni catalysts supported by Gd-doped ceria

A redox cycle between Ce4+ and Ce3+ is an elementary step in water gas shift (WGS) mechanism. By facilitating the redox cycle between +4 and +3 of cerium, a formation of oxygen vacancy can be enhanced. It is considered to be a dominating factor in developing the WGS performance and the stability of ceria in this work. We have facilitated the redox cycle in CeO2 to enrich the WGS activity. The WGS reaction was carried out on Ni catalyst supported by Gd-doped ceria (GDC) from Daiichi. Ni and Re were added onto GDC by impregnation method to examine the role of Re addition on surface, structural and reducibility, which affected upon their catalytic activities. Rhenium has an influence on increasing the water gas shift performance of Ni/GDC catalysts because it facilitates the redox process at the surface of ceria, disperses Ni particles and enhances oxygen vacancy formation. The results indicate that the water gas shift activity of 1%Re4%Ni/GDC is higher than that of 5%Ni/GDC. The dispersion of active site on the surface of catalyst results in an increase of CO molecule adsorption and acceleration of the redox cycle between Ce4+ and Ce3+ of ceria support via oxygen vacancy generation. Therefore, using a combination of these two effects can enhance the WGS performance.

Methanation of CO2 on bulk Co–Fe catalysts

The efficiency of CO2 methanation was estimated through gas chromatography in the presence of Co–Fe catalysts. Scanning electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy were applied for ex-situ analysis of the catalysts after their test in the methanation reaction. Thermal programmed desorption mass spectroscopy experiments were performed to identify gaseous species adsorbed at the catalyst surface. Based on the experimental results, surface reaction model of CO2 methanation on Co–Fe catalysts was proposed to specify active ensemble of metallic atoms at the catalyst surface, orientation of adsorbed CO2 molecule on the ensemble and detailed reaction mechanism of CO2→CH4 conversion. The reaction step when OH group in the FeOOH complex recombined with the H atom adsorbed at the active ensemble to form H2O molecule was considered as the rate-limiting step.

Adsorption and activation of CO2 molecule on subnanometer-sized anionic vanadium carbide clusters VnC4− (n = 1–6): A theoretical study

Adsorption and activation of CO2 onto small-sized transition metal clusters is of practical importance for the conversion of this molecule to value-added products. We study the efficacy of small anionic vanadium carbide clusters, VnC4− with n = 1–6 towards the aforementioned key step by employing density functional theory based method. One of such clusters has been shown to perform very well in activating N2 molecule as revealed in a recent experiment. The results of our calculations suggest that the binding of CO2 molecule with the anionic vanadium carbide clusters becomes stronger with increase in number of vanadium atoms in the cluster. This adsorption energy trend can be properly rationalized by using the d-band center model. The strong adsorption of CO2 molecule is also accompanied with its high degree of activation. The high activation of CO2 is characterized by a significant amount of charge transfer from the anionic clusters to the molecule. We further find that the activation barrier heights for the dissociation of CO2 to CO and O fragments are considerably small for V4C4− and V5C4− clusters. In particular, V5C4− cluster with an activation barrier of 0.83 eV may serve as a good candidate for activation and dissociation of a CO2 molecule.

Rare earth metal doped nickel catalysts supported on exfoliated graphitic carbon nitride for highly selective CO and CO2 methanation

Rare earth metals like Ce and La oxides have emerged as potential promoter candidates for CO and CO2 methanation due to their unique properties. Herein, we report the synthesis by a facile impregnation method of nickel catalysts supported on exfoliated graphitic carbon nitride with cerium (Ni-Ce/eg-C3N4) and lanthanum (Ni-La/eg-C3N4) as promoters. Compared to Ni/eg-C3N4, the promoted catalysts showed an increased number of mesopores, a higher degree of dispersion of Ni nanoparticles, moderate metal-support interaction, and more surface basic sites. In terms of catalytic performance, Ni-Ce/eg-C3N4 catalyst exhibited the best CO methanation (XCO = 72%, SCH4 = 89%) and CO2 methanation (XCO2 = 83%, SCH4 > 99%) activities at ca. 279 °C and 297 °C, respectively. Considering the very high thermodynamic stability of the CO2 molecule, the temperature to achieve maximum conversion of CO2 was only 18 °C higher than CO, demonstrating the significant effect of the Ce promoter in the adsorption and activation of CO2 molecules. This can be attributed to the generation of sufficient active sites of surface defects or oxygen vacancies originating from the reduction of the CeO2 and Ni-Ce-O solid solution. Additionally, the creation of abundant mesopores in eg-C3N4 support increased the capacity of surface basic sites to promote the adsorption of CO2 molecules. The enhancement of CO2 adsorption and activation sites by the Ce promoter and eg-C3N4 support could be the key factor for the high catalytic activity of CO2 methanation at low temperatures.

Br-Doped CuO Multilamellar Mesoporous Nanosheets with Oxygen Vacancies and Cetyltrimethyl Ammonium Cations Adsorption for Optimizing Intermediate Species and Their Adsorption Behaviors toward CO2 Electroreduction to Ethanol with a High Faradaic Efficiency.

It is a prospective tactic to actualize the carbon cycle via CO2 electroreduction reaction (CO2ER) into ethanol, where the crucial point is to design highly active and selective electrocatalysts. In this work, Br-doped CuO multilamellar mesoporous nanosheets with oxygen vacancies and cetyltrimethyl ammonium (CTA+) cations adsorption were synthesized on Cu foam by one-step liquid-phase method at room temperature. The nanosheets with numerous mesopores and rough edges provided abundant active sites for the adsorption of CO2 molecules and brought about a long retention time for intermediates. The dopant of Br- ions induced copious oxygen vacancies on CuO lattices, thereby reducing the activation energy of CO2 molecules and optimizing intermediate species and their adsorption behaviors, while adsorbed CTA+ cations modulated the O affinity of the Cu sites, favoring *OCH2CH3 intermediate converting to ethanol. The optimized Br1.95%-CuO can effectively catalyze CO2ER to C2H5OH in 0.1 M KHCO3. The faradaic efficiency of C2H5OH reached 53.3% with the partial current density of 7.1 mA cm-2 at a low potential of -0.6 V. In addition, after 14 h CO2ER test at -0.6 V, the current density and faradaic efficiency of C2H5OH on Br1.95%-CuO retained 99.6 and 93.9% of their original values, respectively, indicating its prominent catalytic stability. This work provided a novel strategy for designing a CuO catalyst by nonmetal doping and long-chain organic molecules adsorption with multiple active sites for optimizing intermediate species and their adsorption behaviors toward CO2ER to ethanol.

Enhanced CH4 yields by interfacial heating-induced hot water steam during photocatalytic CO2 reduction

The adsorption and activation of H2O vapor on photocatalyst is highly important for CO2 reduction yet having been overlooked among the large amounts of reports. Herein, we demonstrate a preferential H2O adsorption mechanism to replace the previously assumed competitive adsorption, that is, H2O molecules were pre-adsorbed on the catalytic sites and dissociated to provide protons for the activation of the adsorbed CO2 molecules. Thanks to a photothermal membrane (PM)-induced interfacial heating, the generation of hot steam dramatically increases the partial pressure of water vapor from 17 to 43 kPa at ambient pressure, which favors H2O adsorption on TiO2 surface. The well-designed TiO2+PM system achieves selective reduction of CO2 to CH4 with a high evolution rate of 18.3 μmol g−1 h−1, about 3.3 times of that in the absence of PM. The light-to-heat conversion makes the utilization of light energy more efficient, not merely for the photogeneration of charge carriers.

Enhanced adsorption of CO2 on cellulose and chitosan surface by H2O Co-adsorption

Adsorption of CO2 on biopolymers such as cellulose (CELL) and chitosan (CS) attracts researchers’ interest, in particular, the aerogel formation with high surface area and unique physical properties. In this work, we studiedthe molecular adsorption of CO2 molecule on the CELL and CS surfaces by performing density functional theory (DFT) calculations, using dimeric and trimeric structures as model compounds. The structure of the individual CELL and CS along with the molecular adsorbed CO2 systems CELLCO2 and CSCO2 were investigated using B3LYP/6-311++G(d,p) level of theory. The interaction energy of CELLCO2 indicated a weak physical adsorption process, where CSCO2 showed higher binding energies. The co-adsorption of CO2 and H2O on CELL and CS surfaces was also investigated. The results showed that H2O stabilized the adsorption of the CO2 on CELL and CS surface through hydrogen bond (HB), where the adsorption energies increased in the presence of the H2O molecule. The stability of CELLCO2 and CSCO2 was supported by an increase in the charge transfer process. This result highlighted the role of the humidity for the stabilization of CO2 on biopolymers surface.

RuO2/TiO2 photocatalysts prepared via a hydrothermal route: Influence of the presence of TiO2 on the reactivity of RuO2 in the artificial photosynthesis reaction

The incorporation of TiO2 (at two different loadings) with plasmonic RuO2 nanoparticles (with an average size of (3 ± 0.7) nm) to form nanocomposites is studied. XRD results show that RuO2 is formed in the rutile phase, while high levels of TiO2 forms the rutile phase and lower levels form the anatase phase. XRD also confirms doping of TiO2 with Ru atoms and vice versa (doping of RuO2 with Ti atoms) in the nanocomposites.The effect of TiO2 incorporation on the reactivity of RuO2 in the artificial photosynthesis reaction under visible light (which TiO2 cannot absorb) is dramatic. The activities of the catalysts (once TiO2 is included in the composite) significantly increase, and the selectivity of the reactions change with the formation of CH4 and adsorbed hydrocarbonaceous species found alongside the CO + O2 formed over pure RuO2 catalysts.This is ascribed to the generation of a heterojunction interface in the composite material. Following the absorption of visible light, hot electrons (derived from the RuO2 plasmon) become sufficiently energetic to be transferred to the TiO2 CB. From this level the electrons can generate nascent hydrogen which subsequently reacts with (and reduces) adsorbed CO2 molecules.

Adsorption of CO molecules on anatase TiO2(001) loaded with noble metals M (M = Ir/Pd/Pt): A study from DFT calculations

The structure and electronic behaviour of anatase TiO2(001) surface loaded with noble metal atoms M (Ir, Pd and Pt) are systematically investigated by first-principles calculations. Meanwhile, the adsorption behaviour of CO on M-loaded anatase TiO2 is also studied. The results show that Ir and Pt atoms are more likely to be adsorbed on the O2 C (T1) site, while Pd atom is more easily adsorbed at the Ti5 C (T3) site. Among all of the considered systems, the formation energy of Pd/TiO2 (−2.500 eV) is the lowest one followed with Pt/TiO2 (−4.552 eV) and Ir/TiO2 (−6.298 eV). The adsorption mechanism of CO on the anatase TiO2(001) surface is studied by choosing the most stable configurations. The order of adsorption energy is CO/TiO2 (−1.065 eV) >CO/Pd/TiO2 (−2.535 eV) >CO/Pt/TiO2 (−3.326 eV) >CO/Ir/TiO2 (−3.593 eV). This theoretical study shows the adsorption mechanism of CO on the anatase TiO2(001) and provides guidelines for further exploring the adsorption material with excellent adsorption capacity.

Preparation and characterization of nanocrystalline NiO by the thermal decomposition of oxalate salts for the dehydrogenation of 2-butanol to methyl ethyl ketone

In the present study, highly active nanocrystalline nickel oxide samples were prepared by using a simple, solvent-free, and cost-effective preparation method. Commercial nickel oxalate dihydrate powder was mixed with deionized water to form a soft paste which was sonicated till dryness and then, calcined in static air. The prepared nickel oxide samples were characterized by means of Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and N2 adsorption-desorption techniques. The surface basicity of the prepared oxide samples was measured by adsorption of CO2 molecules followed by desorption measurements using the thermogravimetry (TG) technique. The catalytic activity of the prepared nickel oxide samples towards the dehydrogenation of 2-butanol to methyl ethyl ketone (MEK) was studied at a temperature range of 225-325°C. The effects of calcination temperature, reaction temperature, and weight hourly space velocity WHSV on the catalytic activity were studied to determine the best calcination temperature and the optimum operating conditions. The sample calcined at 400°C showed the highest activity and the optimum operating conditions were found to be at the reaction temperature of 300°C and WHSV of 15 L h-1 g-1. The selectivity to MEK was higher than 85% for all the conducted experiments.

MOF derived bimetallic CuBi catalysts with ultra-wide potential window for high-efficient electrochemical reduction of CO2 to formate

Bimetallic electrocatalysts have been proved to be an effective approach to improve the activity and selectivity of electrochemical reduction reaction of CO2 (CO2RR) to formate. However, the activity of catalyst and selectivity of formate are still unsatisfactory. Herein, the rod-like CuBi bimetallic catalysts were synthesized by carbonization and oxidation of CuBi-MOF precursors. Owing to the formation of Bi2CuO4 in the interface of catalyst, the activity and selectivity of the bimetallic CuBi catalysts were greatly enhanced, showing an allured high FEformate of 100 % at −0.77 V (vs. RHE), ultra wide potential window of 900 mV, and excellent durability in H-cell. The in-situ FT-IR and DFT calculation demonstrated that the HCOO* pathway was dominant. Bi2CuO4 can boost the CO2 molecules adsorption capacity and enhance the charge transfer capacity, which benefit its activity and formate selectivity for CO2RR. This work offers insights in improving the catalytic performance of bimetallic catalysts for CO2RR.

Fabrication of porous octahedron-flowerlike microsphere NH2-UiO-66/CdIn2S4 heterojunction photocatalyst for enhanced photocatalytic CO2 reduction

Solar-driven carbon dioxide (CO2) photoreduction has been considered as an environmentally friendly and promising strategy to utilize solar energy and mitigate the impact of greenhouse effect. Designing novel cost-effective photocatalytic system with high CO2 molecules adsorption activity is an efficient avenue to enhance CO2 photoreduction performance. Herein, a series of NH2-UiO-66/CdIn2S4 (NU66/CIS) photocatalysts with different NU66 contents were constructed via facile in-situ hydrothermal route and displayed graceful morphology. According to a series of characterization results, porous octahedron NU66 were deeply anchored on flowerlike 3D-microspheres CIS, and a part of the small-sized CIS were evenly dispersed on the surface of NU66. Without any sacrificial agent, the optimized 8% NU66/CIS heterojunctions still exhibited the satisfactory photocatalytic efficiency for CO2 conversion, whose CO and CH4 yields reached up to 11.24 μ mol g−1 h−1 and 2.92 μ mol g−1 h−1, respectively, which were 2.87 and 3.31 folds higher than that of pristine CIS. The remarkably boosted activity of NU66/CIS was originated from the high specific surface area and the formation of heterostructure between the well-dispersed NU66 and CIS, which could promote the electron transfer during CO2 photocatalytic reduction.

Enhancement of Hydrogen Production Using Ni Catalysts Supported by Gd-Doped Ceria

A redox cycle between Ce4+ and Ce3+ is the elementary step in water gas shift (WGS) mechanism. Facilitating a redox cycle between +4 and +3 of cerium enhanced the formation of oxygen vacancy which is considered as a dominate factor for developing the WGS performance and stability of ceria material. Therefore, in this work, we have tried to facilitate the redox cycle in CeO 2 to enrich the WGS activity. The WGS reaction was carried out on Ni catalyst supported by Gd-doped ceria (GDC). Gd-doped ceria material from Daiichi was employed as support for water gas shift reaction. Ni and Re were added onto GDC by impregnation method to examine the role of Re addition on surface, structural and reducibility which was altered to their catalytic activities. An influence of rhenium on increasing the water gas shift performance of Ni/GDC catalysts since Re facilitating the redox process at the ceria surface, dispersing Ni particles and oxygen vacancy formation. The results of water gas shift activity tests presented that the activity of 1%Re4%Ni/GDC was higher than that of 5%Ni/GDC. The role of Re on improving the WGS activity was promoting the dispersion of active metal site on catalyst surface which result in increases CO molecules adsorption and accelerating a redox cycle between Ce4+ and Ce3+ of ceria support by oxygen vacancies generation. Therefore, the WGS performance can be enhanced by the combination of these two effects.

Probing Monomer and Dimer Adsorption Trends in the MFI Framework.

Porous aluminosilicates such as zeolites are ubiquitous catalysts for the production of high-value and industrially relevant commodity chemicals, including the conversion of hydrocarbons, amines, alcohols, and others. Bimolecular reactions are an important subclass of reactions that can occur on Brønsted acid sites of a zeolite catalyst. Kinetic modeling of these systems at the process scale requires the interaction energetics of reactants and the active sites to be described accurately. It is generally known that adsorption is a coverage-dependent phenomenon, with lower heats of adsorption observed for molecules at higher coverage. However, few studies have systematically investigated the coadsorption of molecules on a single active site, specifically focusing on the strength of interaction of the second adsorbate after the initial adsorption step. In this work, we quantify the unimolecular and bimolecular adsorption energies of varying adsorbates, including paraffins, olefins, alcohols, amines, and noncondensible gases in the acidic and siliceous ZSM-5 frameworks. As a special case, olefin adsorption was examined for physisorption and chemisorption regimes, characterized by π-complex, framework alkoxide and carbenium ion adsorption, respectively. The effects of functional groups and molecular size were quantified, and correlations that relate the adsorption of the second adsorbate identity to that of the first adsorbate are provided.