Undesired CO Research Articles

A two-stage Ce/TiO2–Cu/CeO2 catalyst with separated catalytic functions for deep catalytic combustion of CH2Cl2

For the deep combustion of dichloromethane (DCM), a novel two-stage Ce/TiO2–Cu/CeO2 catalyst was designed and its catalytic performance was investigated in this study. It yielded a remarkable catalytic activity. The degradation efficiency reached up to 97.0% at 330°C with less undesired CO, Cl2 and byproducts (CxHyClz) in dry air. The DCM conversion and the yield of CO2 maintained during the long time test, even in the presence of water. Based on the comparison of catalytic performance and catalyst characterization of Ce/TiO2 and (Ce+Cu)/TiO2, a three-step degradation mechanism for DCM was proposed. The mechanism consisted of adsorption and rupture of the C–Cl bonds, deep oxidation of C–H from byproducts and total oxidation of CO to CO2, which afforded the theoretical basis for the design of the novel two-stage catalytic system. In the novel two-stage Ce/TiO2–Cu/CeO2 system, the rupture of C–Cl and the total oxidation of CO were physically isolated. This separated arrangement not only avoided the decrease of acid sites happened on (Ce+Cu)/TiO2 catalyst, but also avoided the chlorine poisoning of TiO2 due to the strong adsorption of Cl on the CuO. Moreover, CuO itself had high resistance to the toxicity of Cl.

Intermetallic GaPd2 Nanoparticles on SiO2 for Low-Pressure CO2 Hydrogenation to Methanol: Catalytic Performance and In Situ Characterization

A nanodispersed intermetallic GaPd2/SiO2 catalyst is prepared by simple impregnation of industrially relevant high-surface-area SiO2 with Pd and Ga nitrates, followed by drying, calcination, and reduction in hydrogen. The catalyst is tested for CO2 hydrogenation to methanol at ambient pressure, revealing that the intrinsic activity of the GaPd2/SiO2 is higher than that of the conventional Cu/ZnO/Al2O3, while the production of the undesired CO is lower. A combination of complementary in situ and ex situ techniques are used to investigate the GaPd2/SiO2 catalyst. In situ X-ray diffraction and in situ extended X-ray absorption fine structure spectroscopy show that the GaPd2 intermetallic phase is formed upon activation of the catalyst via reduction and remains stable during CO2 hydrogenation. Identical location–transmission electron microscopy images acquired ex situ (i.e., micrographs of exactly the same catalyst area recorded at the different steps of activation and reaction procedure) show that nanopartic...

Zinc-Rich Copper Catalysts Promoted by Gold for Methanol Synthesis

In this study, we gathered further understanding of the function of the components in the Cu-ZnO-Al2O3 catalyst for methanol synthesis from mixed syngas feeds (CO/CO2/H2) to rationally develop systems displaying superior performance. In order to unravel the role of ZnO in the hydrogenation of the preferred methanol source, CO2, and in the (reverse) water–gas shift ((R)WGS) reaction, we tested coprecipitated materials with variable surface zinc content under industrially relevant conditions (5.0 MPa, 503–543 K). We found that a surface enrichment in zinc leads to higher activity and selectivity due to (i) the enhancement of the unique synergistic Cu-ZnO interactions boosting CO2 hydrogenation, (ii) the inhibition of the RWGS reaction which produces the undesired CO, and (iii) the electronic stabilization of the Cu sites against reoxidation by CO2 or H2O. Thus, a catalyst with a surface Zn/(Cu + Zn) ratio of 0.8 displayed superior catalytic properties than a commercial benchmark sample, which featured only ...

Carbon nanotubes/aluminum composite as a hydrogen source for PEMFC

Al matrix composites reinforced with 0–5 vol. % carbon nanotubes (CNTs) were fabricated by spark plasma sintering (SPS) to examine their hydrogen generation properties from the hydrolysis of Al in 10 wt. % NaOH solution at room temperature. The 5 vol. % CNTs/Al composite exhibits a maximum hydrogen generation rate of 120 ml/min g, which is about 6 times higher than that of Al without CNTs due to the synergetic effects of the porous Al matrix, which has a large reaction area and galvanic corrosion between the Al matrix and the CNTs. The hydrogen gas generated from the hydrolysis of the CNTs/Al composite has high purity without any production of undesirable CO. PEMFC produced electricity at 10 A and 0.73 V for 13 min, with hydrogen generated from the hydrolysis of 3.5 g–5 vol. % CNTs/Al composite. The CNTs/Al composite was effectively used as a hydrogen source for PEMFC.

Review of hydrogen-enriched gas production from steam gasification of biomass: The prospect of CaO-based chemical looping gasification

Abstract Global warming, climate change and energy security issues are the forces driving the fossil fuel based energy system towards renewable and sustainable energy. Hydrogen as a clean energy carrier is believed to be the most promising source to replace fossil fuel. Biomass gasification with the presence of steam offers a feasible, sustainable, and environment-friendly option as well as a favorable alternative for higher hydrogen yields and for large-scale hydrogen production which can satisfy the need of hydrogen in the future. However, the process suffers from the problem of undesirable CO 2 and tar formation. Calcium oxide (CaO) has been acknowledged as a catalyst to produce hydrogen-rich gas and has currently gained broad attention due to its cheapness and abundance. Nevertheless, the deactivation of CaO after carbonation reaction is challenging for continuous hydrogen production and economical perspective. To conquer such challenge, the concept of CaO-based chemical looping gasification (CaO-based CLG) has emerged recently. Additionally, due to its energy-efficient and environment-friendly aspects, the CaO-based CLG using biomass as feedstock is gaining more attention in recent years. This study first presents a review on conventional steam gasification of biomass without catalysts for producing hydrogen-rich product gas. The effects of key variables, such as biomass characteristics, gasifier temperature, steam-to-biomass ratio (S/B) and equivalence ratio (ER), on hydrogen-enriched gas production are discussed based on recent researches and developments. Then the use of CaO in biomass steam gasification for hydrogen production with in situ CO 2 capture and tar reduction is described. The prospect of CaO-based CLG using biomass fuel is also discussed as a promising process for renewable, sustainable and environment-friendly hydrogen production.

Thermodynamic Analysis for Quantifying Fuel Cell Grade H2 Production by Methanol Steam Reforming

AbstractSteam reforming of methanol in fixed‐bed and hybrid reactors, namely, traditional fixed‐bed reactor (FBR1), fixed‐bed reactor with H2‐selective membrane (FBR2), and fixed‐bed reactor with CO2 adsorption (FBR3) is thermodynamically analyzed. The performance of these reactors is compared in terms of quality and quantity of H2 production for fuel cell application. In FBR2 and FBR3, the contents of undesired products CO, CH4, and carbon are highly reduced.

From Oxide‐Supported Palladium to Intermetallic Palladium Phases: Consequences for Methanol Steam Reforming

AbstractThis Minireview summarizes the fundamental results of a comparative inverse‐model versus real‐model catalyst approach toward methanol steam reforming (MSR) on the highly CO2‐selective H2‐reduced states of supported Pd/ZnO, Pd/Ga2O3, and Pd/In2O3 catalysts. Our model approach was extended to the related Pd/GeO2 and Pd/SnO2 systems, which showed previously unknown MSR performance. This approach allowed us to determine salient CO2‐selectivity‐guiding structural and electronic effects on the molecular level, to establish a knowledge‐based approach for the optimization of CO2 selectivity. Regarding the inverse‐model catalysts, in situ X‐ray photoelectron spectroscopy (in situ XPS) studies on near‐surface intermetallic PdZn, PdGa, and PdIn phases (NSIP), as well as bulk Pd2Ga, under realistic MSR conditions were performed alongside catalytic testing. To highlight the importance of a specifically prepared bulk intermetallicoxide interface, unsupported bulk intermetallic compounds of PdxGay were chosen as additional MSR model compounds, which allowed us to clearly deduce, for example, the water‐activating role of the special Pd2Ga‐β‐Ga2O3 intermetallicoxide interaction. The inverse‐model studies were complemented by their related “real‐model” experiments. Structure–activity and structure–selectivity correlations were performed on epitaxially ordered PdZn, Pd5Ga2, PdIn, Pd3Sn2, and Pd2Ge nanoparticles that were embedded in thin crystalline films of their respective oxides. The reductively activated “thin‐film model catalysts” that were prepared by sequential Pd and oxide deposition onto NaCl(001) exhibited the required large bimetaloxide interface and the highly epitaxial ordering that was required for (HR)TEM studies and for identification of the structural and catalytic (bi)metalsupport interactions. To fully understand the bimetalsupport interactions in the supported systems, our studies were extended to the MeOH‐ and formaldehyde‐reforming properties of the clean supporting oxides. From a direct comparison of the “isolated” MSR performance of the purely bimetallic surfaces to that of the “isolated” oxide surfaces and of the “bimetaloxide contact” systems, a pronounced “bimetaloxide synergy” toward optimum CO2 activity/selectivity was most evident. Moreover, the system‐specific mechanisms that led to undesired CO formation and to spoiling of the CO2 selectivity could be extracted.

Comparative thermodynamic analysis of adsorption, membrane and adsorption-membrane hybrid reactor systems for methanol steam reforming

The thermodynamic analysis of steam reforming of methanol without and with fractional removal of H2 and CO2 in adsorption, membrane and adsorption-membrane hybrid reactor systems to produce fuel cell grade H2 with minimal carbon formation is investigated. The results indicate that the removal of undesired CO2 by CO2 adsorbent is most effective process for the production of high purity H2 than H2 removal by membrane. However, the membrane is effective only above 30% H2 removal. It is possible to obtain H2 yield of 2.6 with negligibly small amount of CO and carbon formation at T = 405 K, P = 1 atm, 80% removal of CO2 and 100% methanol conversion. Identical results are achieved even at lower temperature of 345 K in adsorption-membrane hybrid reactor system at 80% removal of H2 and CO2. Thus high grade H2 can be produced by single step process and further processing to reduce CO by PROX reactor is not necessary.

In situ study of the formation and stability of supported Pd2Ga methanol steam reforming catalysts

Pd/Ga2O3 methanol steam reforming (MSR) catalysts were characterized in detail by utilizing a range of in situ techniques of varying surface sensitivity. Correlating the nature of the intermetallic Pd–Ga compound (IMC; formed upon reduction) with the corresponding activity/selectivity revealed pronounced differences. Generally, a dynamic response of the catalyst surface to the surrounding gas environment was observed. Special attention was paid to the bulk and surface stability of the Pd–Ga IMCs. Whereas the bulk was stable in O2, decomposition of the surface occurred resulting in a partial coverage by GaxOy islands. In addition, the main formation mechanism of undesired CO and therefore the reason limiting the selectivity to MSR were identified. CO was shown to have a detrimental effect on the selective Pd–Ga intermetallic compound, causing partial decomposition of the IMC to metallic Pd at the surface. Consequently, patches of Pd metal are present under reaction conditions, catalyzing the unwanted parallel methanol decomposition reaction.

Appraisal of a De-NOx System Based on H2 for Light-Duty Diesel Engine Vehicles

The present paper describes a novel, fully integrated after-treatment system based on the use of hydrogen for de-NO x purposes, designed for light-duty diesel engine applications. Hydrogen is generated by an autothermal reformer, placed as a bypass unit of the close-coupled DOC and DPF, and it promotes an NO, reduction in a specific catalytic converter in the under-floor position. The results of the tests on commercial reforming catalysts and on H 2 -selected catalytic reductions (SCR) perovskite catalysts that were synthesized by our group are presented. The best catalyst, on the basis of TPRe activity tests, was La 0.8 Sr 0.2 Fe 0.9 Pd 0.1 O 3 . At a lab-scale, the fuel penalty of the system is around 4% for an NO x to N 2 conversion of 60%, under the best operating conditions. T 50 is very low (150 °C) compared to other de-NO, strategies. The system was then integrated on board a vehicle, and several testing protocols were performed (NEDC2000 cycle, stationary driving conditions on the roller test bench, and real driving conditions on the road). It has been demonstrated that the system is able to work independently in many driving conditions and that the reforming reaction can be effectively controlled and maintained. The NO x emissions were kept below Euro 6 levels, even though undesired CO and HC secondary emissions were produced. This performance was reached with a fuel penalty of 10%. Although this value is presently too high to envisage direct application on the market, it has been demonstrated that this technology is already fully functional on board a real vehicle, which encourages further refining research activity.

Production of NiTi shape memory alloys via electro-deoxidation utilizing an inert anode

NiTi shape memory alloys (SMA) with equiatomic composition of Ni and Ti were prepared by electro-deoxidation, in molten calcium chloride, at 950 °C. Constant voltage electro-deoxidation was conducted using a NiTiO 3 cathode, and either a carbon anode or a novel CaRuO 3/CaTiO 3 composite inert anode. Both anode materials successfully allowed NiTi shape memory alloy to be obtained. The primary difference is that molecular oxygen was produced on the inert anode, instead of environmentally undesired CO 2 greenhouse gases on the carbon anode. Indeed, it was found that carbon could successfully be substituted with conductive calcium titanate–calcium ruthenate composites for electro-deoxidation. Furthermore, DSC was used to analyze the phase transformation of NiTi shape memory alloys, with results revealing the existence of reversible martensite–austenite phase transformations during the cooling and heating process.

The effect of PdZn particle size on reverse-water–gas-shift reaction

The effect of PdZn particle size on the catalytic activity of Pd/ZnO catalysts for the reverse-water–gas-shift (RWGS) reaction was studied. The PdZn particle size was varied by adjusting Pd loading and reducing the catalysts at different temperatures. XRD and IR spectroscopy characterization confirmed the absence of metallic Pd on the catalyst surface. Consequently, the effect of PdZn alloy particle size on the RWGS reaction can be unambiguously studied without the complication of reactions catalyzed by metallic Pd. The results indicated that the turnover frequency increases as the PdZn crystallite size decreases. Interestingly, this structure relationship between PdZn particle size and RWGS activity is consistent with that previously observed for the steam reforming of methanol, i.e., higher CO selectivity on smaller PdZn particles. Thus, RWGS has been identified as a likely potential reaction pathway to undesired CO formation in methanol steam reforming on Pd/ZnO catalysts for hydrogen production.

Selective Oxidation of Methanol to Hydrogen over Gold Catalysts Promoted by Alkaline‐Earth‐Metal and Lanthanum Oxides

A series of alumina-supported gold catalysts was investigated for the CO-free production of hydrogen by partial oxidation of methanol. The addition of alkaline-earth metal oxide promoters resulted in a significant improvement of the catalytic performance. The methanol conversion was ca. 85 % with all studied catalyst materials, however, the selectivity for hydrogen increased from 15 % to 51 % when going from the unpromoted to a BaO-promoted catalyst. The formation of the undesired byproducts CO, methane, and dimethyl ether was considerably reduced as well. The observed trend in catalyst performance follows the trend in increasing basicity of the studied promoter elements, indicating a chemical effect of the promoter material. Superior catalytic performance, in terms of H(2) and CO selectivity, was obtained with a Au/La(2)O(3) catalyst. At 300 degrees C the hydrogen selectivity reached 80 % with only 2 % CO formation, and the catalyst displayed a stable performance over at least 24 h on-stream. Furthermore, the formation of CO was found to be independent of the oxygen concentration in the feed. The commercial lanthanum oxide used in this study had a low specific surface area, which led to the formation of relative large gold particles. Therefore, the catalytic activity could be enhanced by decreasing the gold particle size through deposition on lanthanum oxide supported on high-surface-area alumina.

High temperature water–gas shift reaction over hollow Ni–Fe–Al oxide nano-composite catalysts prepared by the solution-spray plasma technique

Abstract The effect of Fe content in Ni–Fe–Al oxide nano-composites prepared by the solution-spray plasma technique on their catalytic activity for the high temperature water–gas shift reaction was investigated. The composites showed a hollow sphere structure, with highly dispersed Fe–Ni particles supported on the outer surface of the spheres. When the water–gas shift reaction was performed over an Ni–Al oxide composite catalyst without Fe, undesired CO methanation took place predominantly compared to the water–gas shift reaction, and significant amounts of hydrogen were consumed. When appropriate amounts of Fe were added to the Ni–Al oxide composite catalyst during the plasma process, methanation was suppressed remarkably, without serious loss of activity for the water–gas shift reaction. The catalyst was characterized by STEM, XRD and H2 chemisorption measurements.

MEMS fuel cell system integrated with a methanol reformer for a portable power source

MEMS fuel cell system was designed and fabricated for a portable power source in the present study. The system consists of a methanol–steam reformer, catalytic combustor, preferential oxidation (PROX) reactor, and polymer electrolyte membrane fuel cell (PEMFC). Methanol reformer is an essential part for hydrogen supply, in which a pre-heater, vaporizing/reforming channels and catalytic combustor were integrated. All components were fabricated using MEMS fabrication technologies combined with catalyst loading processes. Performance of the MEMS fuel cell system was measured with the optimal conditions of the reformer and PROX. Power density was 195 mW/cm 2 when the potential was 0.64 V. The performance was low compared to the result for pure hydrogen because the feed at the fuel cell included undesired CO, CO 2, and N 2. MEMS fuel cell system with a weight specific energy density of 225 W h/kg was accomplished as an alternative micro power source.

In situ DRIFTS investigation of the steam reforming of methanol over Pt/ceria

In situ DRIFTS was used to probe the reaction mechanism of steam reforming of methanol over 1% Pt/ceria. Links were drawn between those results and the results of catalytic testing in a fixed bed reactor, including switching studies between deuterated and non-deuterated feeds. The steam reforming mechanism is suggested to proceed via adsorbed methoxy, formate, and carbonate species, and is selective at low conversion. At higher conversions, CO 2 reacts via reverse water–gas shift via surface formate intermediates to produce significant levels of undesired CO product.

Oxidative reforming of bio-ethanol over CuNiZnAl mixed oxide catalysts for hydrogen production

Hydrogen (H2) is expected to become an important fuel for the future to be used as an energy carrier in automobiles and electric power plants. A promising route for H2 production involves catalytic reforming of a suitable primary fuel such as methanol or ethanol. Since ethanol is a renewable raw material and can be cheaply produced by the fermentation of biomass, the ethanol reforming for H2 production is beneficial to the environment. In the present study, the steam reforming of ethanol in the presence of added O2, which in the present study is referred to as oxidative steam reforming of ethanol (OSRE), was performed for the first time over a series of CuNiZnAl mixed oxide catalysts derived from layered double hydroxide (LDH) precursors. The effects of Cu/Ni ratio, temperature, O2/ethanol ratio, contact time, CO co-feed and substitution of Cu/Ni by Co were investigated systematically in order to understand the influence of these parameters on the catalytic performance. An ethanol conversion close to 100% was noticed at 300 °C over all the catalysts. The Cu-rich catalysts favor the dehydrogenation of ethanol to acetaldehyde. The addition of Ni was found to favor the C–C bond rupture, producing CO, CO2 and CH4. Depending upon the reaction condition, a H2 yield between 2.5 and 3.5 moles per mole of ethanol converted was obtained. A CoNi-based catalyst exhibited better catalytic performance with lower selectivity of undesirable byproducts, namely CH3CHO, CH4 and CO.

The Reduction of NO by Propene over Ba-Promoted Pt/γ-Al2O3 Catalysts

The performance of Ba-promoted Pt/γ-Al2O3 catalysts in the reduction of NO by propene has been investigated in a wide range of temperatures (ca. 200–500°C), reactant partial pressures, and promoter loading. The reaction follows Langmuir–Hinshelwood-type kinetics, reflecting weaker adsorption of NO on the metal surface relative to C3H6. Both catalytic activity and selectivity are strongly promoted by Ba, which does not however induce a change in the reaction mechanism. Rate increases by 2 orders of magnitude are achievable for N2 and CO2 production, while the selectivity toward N2 is also significantly improved with a gain of about 50– 60 percentage units exhibited by optimally Ba-promoted Pt. Barium also suppressed the formation of the undesirable by-product CO. These effects are understandable in terms of the influence of the Ba promoter on the relative adsorption strengths of reactant species. Ba promotes the adsorption (increasing coverage) of electronegative adsorbates (NO) relative to the adsorption of electropositive adsorbates (propene) on a catalyst surface predominately covered by the hydrocarbon. This is accompanied by weakening of the N–O bond, thus facilitating NO dissociation. These effects operate together to produce large increases in both activity and selectivity.

High selectivities to ethylene by partial oxidation of ethane

At least 85 percent selectivity to ethylene at greater than 70 percent conversion can be obtained by partial oxidation of ethane by adding large amounts of H(2) to the reaction mixture and using a platinum-tin catalyst operating at 950 degrees C with a contact time of approximately 10(-3) seconds. This system almost totally shuts off the reactions that form undesired CO and CO(2), which fall from 20 percent without H(2) to 5 percent when H(2) is added. Although a 2/1 H(2)/O(2) mixture should be explosive at high temperatures, no flames or explosions occur in the presence of ethane. The successive reactions on the catalyst generate more H(2) than used in the feed, so with recycle no additional H(2) would be needed. These results are unexpected because ethylene is a nonequilibrium product and entropy considerations argue that all reaction channels open at high temperatures so the products should approach equilibrium, which predicts only a few percent ethylene. This process is promising for the replacement of steam cracking in the production of ethylene.

Simultaneous catalytic reduction of NO and N2O using Fe-MFI prepared by solid-state ion exchange

Solid-state ion exchange in the presence of air has been used to prepare Fe-MFI catalysts that exhibit activities comparable to preparations obtained under anaerobic conditions. Preliminary results obtained during the simultaneous catalytic reduction of NO and N2O with propane in the temperature range from 473 to 773 K show that Fe-MFI might be of interest for the treatment of exhaust gases containing NOx and nitrous oxide. Undesirable CO formed in a side-reaction can be oxidized to CO2 by promotion of Fe-MFI with small amounts of Pt.