Catalytic System For Conversion Research Articles

Research Progress on Lignin Depolymerization Strategies: A Review.

As the only natural source of aromatic biopolymers, lignin can be converted into value-added chemicals and biofuels, showing great potential in realizing the development of green chemistry. At present, lignin is predominantly used for combustion to generate energy, and the real value of lignin is difficult to maximize. Accordingly, the depolymerization of lignin is of great significance for its high-value utilization. This review discusses the latest progress in the field of lignin depolymerization, including catalytic conversion systems using various thermochemical, chemocatalytic, photocatalytic, electrocatalytic, and biological depolymerization methods, as well as the involved reaction mechanisms and obtained products of various protocols, focusing on green and efficient lignin depolymerization strategies. In addition, the challenges faced by lignin depolymerization are also expounded, putting forward possible directions of developing lignin depolymerization strategies in the future.

Recent Advances in Zeolites-Catalyzed Biomass Conversion to Hydroxymethylfurfural: The Role of Porosity and Acidity.

Biomass is an attractive raw material for the production of fuel oil and chemical intermediates due to its abundant reserves, low price, easy biodegradability, and renewable use. Hydroxymethylfurfural (5-HMF) is a valuable platform chemically derived from biomass that has gained significant research interest owing to its economic and environmental benefits. In this review, recent advances in biomass catalytic conversion systems for 5-HMF production were examined with a focus on the catalysts selection and feedstocks' impact on the 5-HMF selectivity and yield. Specifically, the potential of zeolite-based catalysts for efficient biomass catalysis was evaluated given their unique pore structure and tunable (Lewis and Brønsted) acidity. The benefits of hierarchical modifications and the interactions between porosity and acidity in zeolites, which are critical factors for the development of green catalytic systems to convert biomass to 5-HMF efficiently, were summarized and assessed. This Review suggests that zeolite-based catalysts hold significant promise in facilitating the sustainable utilization of biomass resources.

Mixed-terminal MXenes react with SF6 in aqueous solution: reaction mechanism and pathway

The search for an ecofriendly treatment for the strong greenhouse gas SF6 has become a global hot issue. Herein, the mixed-terminal Ti3C2T x MXene catalyzing conversion of SF6 in aqueous solution was explored. The catalytic network on realistic Ti3C2T x was constructed. By theoretical calculations, target products and the microscopic reaction mechanism were studied. Firstly, SF6 exhibited different degrees of chemisorption on the constructed Ti3C2T x surfaces of three varying terminal proportions, with different terminals showing synergistic effects. Secondly, taking the effect of H2O and surface hydroxyl into account, the catalytic conversion system of SF6 on a Ti3C2(OH)0.66O1.33 surface was constructed, containing 25 sub-reactions with H2S as one of the final products. SF6 went through successive defluorination on the Ti3C2(OH)0.66O1.33 surface to form low-fluorine sulfide SF x (x = 5, 4, 3, 2, 1), with energy of 80.685 kcal mol−1 released during the whole process. The energy barriers of all the SF6 decomposition sub-reactions were significantly lower than that in free space. Besides, O terminals were regarded as potential hydroxyl terminals in aqueous solution, which continuously provided active hydroxyl groups for the Ti3C2(OH)0.66O1.33 surface. Thus, SF6 conversion in aqueous solution will not result in deactivation of Ti3C2T x catalyst. This work provides a theoretical basis for MXene to catalyze SF6 decomposition in an efficient way.

Highly Efficient Conversion of Xylose Residues to Levulinic Acid over FeCl3 Catalyst in Green Salt Solutions

The economically viable synthesis of levulinic acid (LA), a promising and valuable renewable biomass-derived platform for bioproducts, with high carbon efficiency is a challenge. A direct and highly effective catalytic system for conversion of xylose residues (XRs) into LA under mild conditions by using FeCl3 as catalyst and cheaply available NaCl as promoter has been developed. The NaCl solution exhibits high carbon efficiency in LA (68.0 mol %) when compared with the non-NaCl systems (48.5 mol %) due to the moderate increase of the acidity and the higher viscosity of the NaCl system than water. The experimental results demonstrated that the presence of NaCl caused no distinctive changes on reaction pathways but increased the dissolution rate and the hydrolysis rate of XRs cellulose. Moreover, further integration of our degradation process with a reactive extraction step makes energy-efficient separation of LA. The NaCl solutions easily and efficiently extracted LA into LA-derived solvent 2-methyltetrahy...

Development of a Complex Catalytic Conversion System for Internal Combustion Engines Fueled with Natural Gas

The paper related to developing of a new gas engines with high energy efficiency and meeting future emission standards. It is necessary to develop complex exhaust gas aftertreatment systems to treat the toxic components efficiently when the engine runs on stoichiometric and lean mixtures. It is proposed to use new combination of three-way catalyst for working on stoichiometric mixtures and a selective catalytic reduction system for NOx aftertreatment on lean mixtures. Experimental studies have shown that efficient (over 90%) conversion of gas engine exhaust components takes place in the range of air excess ratio from 0.99 to 1.01. Theoretical studies have shown that the highest efficiency of nitrogen oxides reduction is achieved in the temperature range of 400...500°C and reaches over 97%.

Model-based optimization of injection strategies for SI engine gas injectors

A mathematical model for the prediction of the mass injected by a gaseous fuel solenoid injector for spark ignition (SI) engines has been realized and validated through experimental data by the authors in a recent work [1]. The gas injector has been studied with particular reference to the complex needle motion during the opening and closing phases. Such motion may significantly affect the amount of injected fuel. When the injector nozzle is fully open, the mass flow depends only on the upstream fluid pressure and temperature. This phenomenon creates a linear relationship between the injected fuel mass and the injection time (i.e. the duration of the injection pulse), thus enabling efficient control of the injected fuel mass by simply acting on the injection time. However, a part of the injector flow chart characterized by strong nonlinearities has been experimentally observed by the authors [1]. Such nonlinearities may seriously compromise the air-fuel mixture quality control and thus increase both fuel consumption and pollutant emissions (SI engine catalytic conversion systems have very low efficiency for non-stoichiometric mixtures). These nonlinearities arise by the injector outflow area variation caused by needle impacts and bounces during the transient phenomena, which occur in the opening and closing phases of the injector. In this work, the mathematical model previously developed by the authors has been employed to study and optimize two appropriate injection strategies to linearize the injector flow chart to the greatest extent. The first strategy relies on injection pulse interruption and has been originally developed by the authors, whereas the second strategy is known in the automotive engine industry as the peak and hold injection. Both injection strategies have been optimized through minimum injection energy considerations and have been compared in terms of linearization effectiveness. Efficient linearization of the injector flow chart has been achieved with both injection strategies, and a similar increase in injector operating range has been observed. The main advantage of the pulse interruption strategy lies on its ease of implementation on existing injection systems because it only requires a simple engine electronic control unit software update. Meanwhile, the peak and hold strategy reveals a substantial lack of robustness and requires expressly designed injectors and electronic components to perform the necessary voltage commutation.

A mathematical model for the prediction of the injected mass diagram of a S.I. engine gas injector

A mathematical model of gaseous fuel solenoid injector for spark ignition engine has been realized and validated through experimental data. The gas injector was studied with particular reference to the complex needle motion during the opening and closing phases, which strongly affects the amount of fuel injected. As is known, in fact, when the injector nozzle is widely open, the mass flow depends only on the fluid pressure and temperature upstream the injector: this allows one to control the injected fuel mass acting on the “injection time” (the period during which the injector solenoid is energized). This makes the correlation between the injected fuel mass and the injection time linear, except for the lower injection times, where we experimentally observed strong nonlinearities. These nonlinearities arise by the injector outflow area variation caused by the needle bounces due to impacts during the opening and closing transients [1] and may seriously compromise the mixture quality control, thus increasing both fuel consumption and pollutant emissions, above all because the S.I. catalytic conversion system has a very low efficiency for non-stoichiometric mixtures. Moreover, in recent works [2, 3] we tested the simultaneous combustion of a gaseous fuel (compressed natural gas, CNG, or liquefied petroleum gas, LPG) and gasoline in a spark ignition engine obtaining great improvement both in engine efficiency and pollutant emissions with respect to pure gasoline operation mode; this third operating mode of bi-fuel engines, called “double fuel” combustion, requires small amounts of gaseous fuel, hence forcing the injectors to work in the non-monotonic zone of the injected mass diagram, where the control on air-fuel ratio is poor. Starting from these considerations we investigated the fuel injector dynamics with the aim to improve its performance in the low injection times range. The first part of this paper deals with the realization of a mathematical model for the prediction of both the needle motion and the injected mass for choked flow condition, while the second part presents the model calibration and validation, performed by means of experimental data obtained on the engine test bed of the internal combustion engine laboratory of the University of Palermo.

Solvent Effects on the Hydrogenolysis of Diphenyl Ether with Raney Nickel and their Implications for the Conversion of Lignin

The conversion of lignin, the most recalcitrant of the biopolymers, is necessary for a carbon-efficient utilization of lignocellulosic materials. In this context, hydrogenolysis of lignin is a process receiving increasing attention. In this report, the solvent effects on the hydrogenolysis of diphenyl ether and lignin with Raney Ni are addressed. The Lewis basicity of the solvent very much affects the catalytic activity, so Raney Ni in nonbasic solvents is an extremely active catalyst for hydrogenolysis and hydrogenation. In basic solvents, however, Raney Ni is a less active, but much more selective catalyst for hydrogenolysis while preserving the aromatic products. With regard to the reactions with lignin, assessing the complexity of the product mixtures by two-dimensional GC×GC-MS revealed solvent effects on the product distribution. Reaction in methylcyclohexane resulted in cyclic alcohols and cyclic alkanes, whereas reaction in 2-propanol led to cyclic alcohols, cyclic ketones, and unsaturated products. The hydrogenolysis of lignin in methanol, however, produced mostly phenols. Overall, these results demonstrate that the solvent plays a key role in directing the selectivity and, thus, it must be taken into consideration in the design of catalytic systems for conversion of lignin by hydrogenolysis of C-O ether bonds.

추적자 확산 실험에 의한 서울 도심 확산 현상 연구 - 도시규모 대기확산 실험을 위한 PFCs 추적자 방출 및 분석 시스템의 개발 및 적용 연구

The release, sampling and analytical methods have been developed and tested for perfluorocarbons (PFCs) atmospheric tracers in order to gain insight into the atmospheric transport and dispersion over the urban conditions of Seoul, Korea. Although PFCs tracer experiments provide unique opportunities to test local and urban scale of transport and dispersion, no previous experiment with PFCs has been conducted in Korea. PMCH and PDCH were chosen as targeted tracers in our study due to their extreme low ambient concentrations and great sensitivities among various PFCs. For PFCs release system, a set of micro-metering pump, electronic balance, vaporizing furnace and high speed blower was constructed for precise and accurate release of tracers. The precision of released rate by this system was estimated to be 1%. Samplings of PFCs were carried out by fabricated portable air samplers with micro pumps and rotameters into glass tubes packed with 150 mg of Carboxen-569. The uncertainty of these sampling system was maintained below 14%. PMCH and PDCH were quantified in GC/ECD with preconditioned injection system to eliminate the interference compounds using traps and subsequent catalytic conversion system prior to column separation. Three intensive field test were undertaken during the springtime of 2002 to 2004 in eastern part of Seoul. Daily background samples were collected to characterize the background levels of PMCH and PDCH prior to their release. The observed background concentrations of PMCH ranged from 3.5 to 10.1 fL/L and varied randomly in location and time in this study. Its mean and standard variation of background concentration (<TEX>$6.8{\pm}1.9\;fL/L$</TEX>) are higher than those (<TEX>$3.2{\sim}5.8\;fL/L$</TEX>) of other historic tracer studies. Identified uncertainty for background PMCH was <TEX>$1.7{\sim}2.0\;fL/L$</TEX> using this analytical system. Combined relative uncertainty in determining the tracer's concentrations was estimated as 17%. However, its background concentrations and uncertainty in concentration determination were found to be low and stable enough for tracer study.

On-board fuel conversion for hydrogen fuel cells: comparison of different fuels by computer simulations

The conversions of methane, propane, octane and methanol to hydrogen under conditions pertinent to fuel cell operation have been described quantitatively and examined by a series of computer simulations. Catalytic conversion may be achieved by direct partial oxidation or by a combination of total oxidation and steam reforming. Both systems have been simulated, using conversion data and kinetic equations reported in the literature for various catalyst configurations and hydrocarbons. The results show that, in terms of hydrogen produced per weight of fuel and water carried, direct partial oxidation of propane or oxidation/steam reforming of octane are the best alternatives. The latter possess the ease of operation but coke formation may be more of a problem. Methanol, often suggested as a fuel, is much less efficient. Operation of a vehicle using the catalytic conversion system would require fueling by both hydrocarbon and water.

Mathematical modelling of precious metals catalytic converters for diesel NOx reduction

Precious metal catalysts for NO x reduction in lean diesel engine exhaust conditions are characterized by a narrow temperature range of efficient operation and require high availability of reducing species in significant concentration. Consequently, there exists a large optimization potential in the design and control of lean-NO x catalytic conversion systems. A mathematical model of the transport and chemical phenomena in platinum-based lean-NO x catalysts was formulated, based on the experience with analogous models for gasoline three-way catalysts. A simplified four-reaction scheme is employed, considering the oxidation of CO, H2 and hydrocarbons (HCs), as well as the reaction between NO x and HCs. Results are compared with previously published laboratory and engine data in order to assess the capacity of this approach in representing real-world behaviour of Pt-based lean-NO x catalysts. Initial results illustrate the power and flexibility of the model, which is able to predict the NO x conversion characteristics in model gas tests as well as in full-scale engine tests with reasonable accuracy.

4507397 Semi-continous regeneration of sulfur-contaminated catalytic conversion systems: Waldeen C Buss assigned to Chevron Research Company

4507397 Semi-continous regeneration of sulfur-contaminated catalytic conversion systems: Waldeen C Buss assigned to Chevron Research Company

Basic research needs and opportunities at the solid-gas interface

S—G reactions that may occur at surfaces of devices exposed to the normal solar environment (i.e. ambient air, high UV flux, thermal cycling etc.) are major concern in solar technology. Surfaces of importance include glass and polymer transmitters and polymer coatings generally, all of which may develop microcracks or otherwise fail in solar systems at rates far in excess of those for uniform degradation. An equally important, although less obvious, class of S—G interfaces are those developed sequentially in the manufacture of multilayer devices, e.g. mirrors and photovoltaic converters. Thus, it becomes necessary to know how the properties of a particular component layer are affected by the manufacturing environment (air, vacuum etc.) and especially to know how the overall operation of the device is influenced by the cumulative effect of these various surface reactions. This problem is of special importance in solar applications because of the frequent use of multilayer technology and the long lifetime requirements for components. There are a number of important chemical reactions which involve photoconversion and/or photocatalysis. In these processes, S—G interfaces occur on the catalysts and their support materials. Major research needs include a detailed understanding of semiconductor surfaces with and without chemisorbed species, understanding of the photoconversion and photocatalysis mechanisms, effects of sensitizers, understanding of spill-over phenomena, theoretical calculations and new experimental methods for analysis of the S—G interface under ambient pressure. In both thermal conversion and catalytic conversion systems the transfer of energy occuring at S—G interfaces is very important. The problem is not simple, especially under high UV fluxes and on non-metallic systems. It is conceivable that useful resonant energy transfers may be predictable.