Decreasing supplies of high quality crude oil and increasing demand for high quality distillates have motivated the interest in converting natural gas to liquid fuels, especially with the present boom in natural gas proven reserves. Nevertheless, one major issue is the curtailment of costs incurred in producing synthesis gas from natural gas, which account for approximately 60% of the costs used in producing liquid fuels. While there are three main routes to convert natural gas to syngas: steam reforming (SMR), partial Oxidation (POX) and auto-thermal reforming (ATR). Significant new developments and improvements in these technologies, established innovative processes to minimize greenhouse gases emission, minimize energy consumption, enhance syngas processes, adjust the desired H 2/CO ratio and change the baseline economics. This article reviews the state of the art for the reforming of natural gas to synthesis gas taking into consideration all the new innovations in both processes and catalysis.
In the last few years, natural gas, a non-renewable energy source of primary energy, has been utilized as a feed stock for several industrial high value-added productions and also as environmentally clean and easily transportable fuel due to its abundance and enormous surplus in remote areas and underground resources. The use of natural gas causes a rise in global concentration of green house gases [
Searching for alternative energy sources to replace petroleum based fuels, natural gas has attracted the interest of many researchers and the large amount of methane contained in natural gas has been considered as an input in the production of other high-value products such as syngas and high purity hydrogen.
Syngas, a mixture of H2 and CO, forms the feed stock in the chemical and petrochemical industries for the production of methanol, acetic acid, olefins, gasoline, MTBE, Oxo-alcohols, phosgene and synthetic liquid fuels, etc.
In some cases either H2 or CO is utilized, for which H2 and CO are acquired from synthesis gas. The hydrogen is used in fuel cells, in the production of urea and heavy water, etc. However, the biggest consumer of H2 from syngas is ammonia synthesis. Recently it is being planned to utilize the hydrogen as a fuel for non-polluting vehicle. The carbon monoxide is used in the production of paints, plastics, pesticides, insecticides, acetic acid and ethylene glycol, etc.
For the production of clean fuel like hydrogen to be utilized in fuel cells from natural gas, it is first necessary to bring natural gas to a catalytic process called natural gas reforming. This catalytic process is also known as reforming of methane. Syngas can be produced from a variety of primary feedstock such as coal, petroleum coke, biomass, and natural gas. The lowest cost routes for syngas production, however, are based on natural gas [
Natural gas reforming also known as reforming of methane can be accomplished by means of an exothermic or endothermic reaction depending on the chemical process selected to perform the catalytic reforming of methane.
There are seven reforming processes available for the production of syngas from natural gas, whose major component is methane. These are:
1) Steam Reforming (SMR),
2) Partial Oxidation (POX),
3) Auto Thermal reforming, (ATR),
4) Dry Reforming of methane (DMR),
5) Combined Reforming of methane (CMR),
6) Reforming with Membrane,
7) Tri-reforming of Methane (TMR).
While the top three methods are well established and are widely employed by industry the last four methods are innovations to minimize greenhouse gases emissions, minimize energy consumption and improve the reforming process yields. These methods differ in the composition of syngas produced i.e. their H2/CO ratio as shown in
Steam reforming or steam methane reforming (SMR) is the reaction where steam and hydrocarbons, such as natural gas or refinery feed stock, react in a reformer at temperature of 800˚C - 900˚C and moderate pressure (around 30 bar) in the presence of metal based catalyst for the production of syngas [
Most SMR units include two sections, namely a radiant and a convective section. Reforming reactions take place inside the radiant section. In the convective section, heat is recovered from the hot product gases for preheating the reactants feeds and for generating superheated steam.
Because the process of steam reforming of methane is the reforming process that leads to obtaining syngas with the highest H2/CO ratio, this type of reforming process is considered ideal to obtain a hydrogen gas flow of
high purity from syngas. It is the most widely applied method of producing syngas from natural gas and represents 50% of the global processes of conversion of natural gas for hydrogen production. This percentage reaches 90% in the U.S. Steam reforming of methane is an endothermic process and, therefore, requires very high temperatures, which makes this process very expensive.
Innovated Steam ReformerHeat Exchange Reformers
Basically, a heat exchange reformer is a steam reformer where the heat required for the reaction is supplied predominantly by convective heat exchange. The heat can be supplied from flue gas or process gas or in principle by any other available hot gas. When the heat and mass balance on the process (catalyst) side only is considered, there is no difference between heat exchange reforming and fired tubular reforming, where the heat transfer is predominantly by radiation. This means that all process schemes using heat exchange reforming will have alternatives where the function of the heat exchange reformer is performed in a fired reformer. The process schemes differ “only”, in the amount of heat in flue gas and/or process gas and in the way this heat is utilized.
Types of heat exchange reformers
Three different concepts for heat exchange reformer design have been commercialized by various companies. The three concepts are illustrated in
Types A and B in
It occurs when a sub-stoichiometric fuel-air mixture is partially combusted in a high temperature reformer [
The reactor design of POX and CPOX is presented as a scheme in
POX reactor simply comprises two zones, first the flame part where the hydrocarbons, oxygen, and possibly low amounts of steam react together and second a heat exchanger that recovers the excess heat after the reaction.
In non-catalytic partial oxidation, the production of syngas depends on the air-fuel ratio at operating temperature of 1200˚C - 1500˚C without a catalyst [
The use of catalyst in the production of syngas lowers the required reaction temperature to around 800˚C - 900˚C [
Catalytic partial oxidation can be used only if the sulfur content of natural gas is below 50 ppm. Higher sulfur content would poison the catalyst, so non-catalytic partial oxidation should be used for such fuels.
Two reaction mechanisms have been proposed: one is the “direct mechanism” in which CH4 and O2 react on the adsorbed state on the catalyst surface to yield CO and H2 (Equation 3); the second one is the so-called “combustion-reforming mechanism”. In this latter mechanism, CH4 and O2 first form H2O and CO2 (Equation 4), and then dry (Equation 5) and steam reforming (Equation 1) reactions producing CO and H2.
In addition to these reactions, other side reactions eventually occur. These include
and the formation of solid carbon by the Boudouard reaction
Chemical-Looping Reforming and Combustion
Chemical-looping reforming is a novel process for partial oxidation of hydrocarbon fuel where oxygen is
brought to the fuel by a solid oxygen carrier [
MeO is the oxygen carrier in its oxidized form while Me is the reduced form.
Suitable oxygen carriers include metal oxides such as Fe2O3, NiO, CuO and Mn3O4.
If the fuel is CH4, the oxygen carrier is NiO and the reactor temperature is 1200 K, reaction (8) occurs in the air reactor.
Regeneration:
In the fuel reactor, reactions (equations 9, 10, 1 and 5) may occur, depending on the air ratio. Steam or CO2 could be added to the fuel to enhance the relative importance of reaction (1) or reaction (5) respectively. This could be used to adjust the H2/CO ratio in produced synthesis gas or to suppress formation of solid carbon in the fuel reactor. For chemical-looping combustion as much fuel as possible should be completely oxidized according to reaction (9).
Oxidation:
Partial oxidation:
Chemical-looping reforming is similar to chemical-looping combustion, but complete oxidation of the fuel is prevented by using low air to fuel ratio. Hence chemical-looping reforming can be described as a method for partial oxidation of hydrocarbon fuels that is utilizing chemical-looping as a source of oxygen. This is a considerable advantage compared to conventional technology since the need for expensive and power consuming air separation is eliminated.
The Short Contact Time-Catalytic Partial Oxidation (SCT-CPO) Technology
Precise knowledge of the mechanism of CPOX reaction is of vital importance because of the different thermal effects, which indeed affect both the design and heat management of industrial units [
Initial observation on the occurrence of short contact time hydrocarbon oxidation processes were reported in the years 1992-1993 [
The fast and selective chemistry that is originated is confined inside a thin (<1 mm) solid−gas inter-phase zone surrounding the catalyst particles. Here, the molecules spend 10 - 6 s at temperatures variable between 600˚C - 1200˚C. A key issue for the technological exploitation is in the possibility of avoiding the propagation of reactions into the gas phase that has to remain at a “relatively low” temperature. This condition favors the formation of primary reaction products (namely CO and H2) inhibiting chain reactions. Indeed some experimental studies whose results have been partially described in literature [
By proper choice of the operating conditions, surface temperatures are locally much higher than those predicted by thermodynamic equilibrium calculations assuming adiabatic reactors. The occurrence of the reactions in these local environments determines in some cases conversion and selectivity values higher than those predicted by the thermodynamic equilibrium at the reactor exit temperatures [
i) Small dimensions technical and operational simplicity.
ii) Possibility of modular construction of pre-fabricated and skid mounted units.
iii) Flexibility towards feedstock composition & production capacity.
iv) Reduction of investment costs and energy consumption.
v) Reduction of CO2 production and possibility of an almost complete CO2 capture in case of H2 production plants.
Like other reforming processes of methane, the purpose of the auto-thermal reforming is the production of syngas. Although auto-thermal reforming is an old idea, to date there are only a few commercial sites. The H2/CO
ratio of the syngas obtained in the auto-thermal reforming is a function of the gaseous reactant fractions introduced in the process input. Thus, the H2/CO ratio can be 1 or 2 [
Reactions carried out in the Combustion zone ≈2200 ˚K are given by Equations (4) and (6), and those carried out in the reforming zone 1200 - 1400 ˚K are given by Equations (1) and (5).
By proper adjustment of oxygen to carbon and steam to carbon ratios, the partial combustion in the thermal zone supplies the heat for completing the subsequent endothermic steam and CO2 reforming reactions [
New Auto-Thermal Reactor (KBR)
KBRATR reactor contains a combustion zone at the top and a catalyst filled bed at the bottom. The feedstock is mixed with a sub-stoichiometric amount of oxidant and burned in the combustion zone. There is an intermediate conical recirculation section (see
The resultant gases are passed over the catalyst in the bottom section to achieve as close to an equilibrium mixture as possible.
ATRs are attractive when used in combination with a reforming exchanger. They are also suited for making large volumes of synthesis gas, especially with hydrogen/carbon monoxide ratios such as 1.5/1 - 3/1. These ratios are desirable for synthesis of higher molecular weight hydrocarbons. ATRs have limited commercial experience. One belongs to SASOL in South Africa, which uses ATRs licensed by Lurgi out of Germany. KBR-de- signed ATRs have been installed in ammonia plants in Kitimat, Canada and Liaohe, China [
Since CO2 is available in large quantities and at low costs, CO2 can be used in place of steam for reforming.
Therefore, the dry reforming which is reforming of methane with CO2 seems to be a promising technology for the production of syngas. Dry reforming of methane (DMR) is a process that uses waste carbon dioxide to produce syngas from natural gas. The synthesis gas produced by steam reforming has high H2/CO ratio which is not suitable for Fischer-Tropsch synthesis in the production of long chain higher hydrocarbons due to the excess hydrogen which suppresses chain growth and decreases the selectivity of higher hydrocarbons [
Dry reforming reaction (Equation (5)) is slightly more endothermic than steam reforming. It is favored by low pressure and high temperature [
The dry reforming of methane with CO2 has received special attention in recent years due to two main reasons:
i) It produces syngas with a H2: CO molar ratio that is suitable for products including F-T fuels and DME.
ii) The reaction consumes two types of greenhouse gases, CO2 and CH4 [
The main disadvantage of dry reforming of methane is the significant deposition of carbon on the surface of the catalyst, which contributes to the reduction of its useful life. The main challenge for the industrial application of the reforming of methane with CO2 is related to the development of active catalytic materials, but with a very low coke formation rate, either on the catalysts or in the cold zones of the reactor. The carbon formation in this process can be controlled by using a support that favors the dissociation reaction of CO2 into CO and O, the last species being the responsible for the cleaning of the metallic surface [
A few studies have been reported on simultaneous steam and dry reforming of methane Equation (12) [
The current technology for syngas production requires an oxygen plant for partial oxidation (equation 3); whereas the proposed technology utilizes CO2 using small installation (process intensification) and thus reducing operating and capital cost [
Process Overview
Combination of CO2 reforming and partial oxidation of methane (Equations (3) and (5)) to produce syngas with different precursors
Catalytic dry reforming process is highly endothermic and hence, high energy consumption. Catalytic partial oxidation is an exothermic reaction, so it tends to form hot spots in catalyst beds. It is difficult to control, particularly in a large scale operation. The process of combination of CO2 reforming and partial oxidation of methane (CDPOX) to produce syngas couples the advantages of DMR and POX and offsets the disadvantages of them,
simultaneously [
1) Energy coupling, 2) Controllable product ratio of H2/CO according to the need of the post-process, and 3) A safer operating environment.
Múnera and co workers [
Membrane reactors are non-porous multi component oxides suited to work at temperatures above 1000 K and have high oxygen flux and selectivity. These membranes are known as ion transport membranes (ITM).
In membrane reactors, the oxygen required to perform the CPO reaction is separated from air fed to one side of the membrane at temperatures around 300 K and moderate pressure (0.03 - 0.20 bar) and reacts on the other side with methane and steam at higher pressure (3 - 20 bar) to form a mixture of CO and H2. Then this mixture
can be processed downstream to produce H2 or liquid fuels. The concept of the membrane reactor is depicted in
Dense membranes are permeable to atomic or ionic forms of hydrogen. Pd-Pd alloy membranes offer high permeability only for hydrogen whereas zirconia and perovskites are highly selective only for oxygen. A schematic diagram of a tubular membrane reactor is presented in
According to the low of mass action, and for reversible reactions, removal of one of the reaction products shifts the reaction to the RHS of the reaction equation. Therefore, removal of hydrogen from the reaction products DMR or SMR prevents the reversible reaction in Equations 5 and 1 as well as the RWGSR Equation 11, thus, increases conversion beyond the equilibrium conversion.
Membrane reactors for methane reforming reactions can be categorized according to the type of hydrogen separation membranes and the configuration of reactors and membranes. Dense metal membranes such as palladium and silver-palladium, which show complete perm selectivity toward hydrogen, have been used in hydrogen separation membranes for SMR reactions [
A novel Multi-Channel Membrane Reactor (MCMR) was designed and built for the small-scale production of hydrogen via Steam Methane Reforming (SMR) [
Linde Engineering [
It is a new process designed for the direct production of synthesis gas with desirable H2/CO ratios by reforming methane or natural gas using flue gas from fossil fuel based electric power plants without pre-separation of CO2. These flue gases are regarded as major source of CO2 emission in the U.S. Generally the compositions of flue gases depend on the types of fossil fuels used in power plants. Flue gases from natural gas-fired power plants typically contain:
8% - 10% CO2, 18% - 20% H2O, 2% - 3% O2, and 67% - 72% N2;
Flue gases from coal-fired boilers primarily contain:
12% - 14% CO2, 8% - 10% H2O, 3% - 5% O2, 72% - 77% N2, and trace amount of NOx, SOx, and particulates [
It is hypothesized that tri-reforming be a synergetic combination of CO2 reforming (Equation 5), steam reforming (Equation 1) and methane oxidation reactions (Equation 3 and Equation 4). Therefore, tri-reforming is expected to encompass a number of unique features. One major feature is its ability to convert CO2 in flue gas without CO2 separation while avoiding the use of pure CO2 and the severe problem of carbon deposition encountered in CO2 reforming system [
Other features of tri-reforming include that there is no need to handle pure oxygen and it directly produces synthesis gas with a desirable H2/CO ratio (e.g. H2/CO = 1.5 - 2). Furthermore, oxygen in flue gas may help to ease the reaction energy requirement as encountered in CO2 reforming alone or steam reforming alone. In general, the new tri-reforming process concept is consistent with the goals of DOE Vision 21 for power plants with respect to decreasing green house gas emission, improving power generation efficiency and co-producing fuels and chemicals [
It should be pointed out that the H2/CO ratio in synthesis gas is important since synthesis gas with different H2/CO ratios has different applications in industry. The current major application of synthesis gas (not hydrogen) includes methanol synthesis and Fischer-Tropsch (F-T) synthesis that require synthesis gas with a H2/CO ratio close to 2. However, synthesis gas directly produced from CO2 reforming of methane has H2/CO ratio close to 1. Hence, this kind of synthesis gas (H2/CO ratio ≤1) requires further treatment in order to be applied in methanol and F-T synthesis.
Similarly synthesis gas produced from steam reforming cannot be directly applied in methanol or F-T synthesis either since the H2/CO ratio of synthesis gas produced from steam reforming is usually larger than 3. Although methane partial oxidation produces synthesis gas with a H2/CO ratio of 2, methane partial oxidation is difficult to control due to its exothermic feature and is dangerous and expensive due to the handling of pure oxygen. Tri-reforming, however, is expected to readily produce synthesis gas with the desired H2/CO ratios of 1.5 ~ 2 by manipulating tri-reforming reactant compositions under relatively mild reaction conditions.
The concept of tri-reforming using power plant flue gas was first proposed by [
Tri reforming can also be used for converting and utilizing CO2-rich natural gas [
Steam reforming is the main reforming process of methane that is predominantly utilized because it has the greatest value for H2/CO ratio, i.e., the product of the reforming process is a gas flow considered ideal for the development of the catalytic process of obtaining a gas hydrogen flow of high purity. However, as the process of steam reforming is considered too expensive, the other types of catalytic chemical processes are considered as alternative processes for carrying out the reforming of methane and they were developed with the aim of making savings in thermal energy consumption required for the catalytic process to occur. The choice of process type to reforming of methane must take into consideration the economic viability of the process related to the destination to be given to the syngas produced.
Partial oxidation and auto-thermal reforming are good choices to produce syngas when the value of H2/CO ratio is adequate and especially when it comes to reduce the consumption of thermal energy, a most important factor. In short, it can be said that the selection of the type of catalytic chemical process of reforming of methane depends on the type of application of the syngas produced. A comparison of syngas generation technologies using natural gas as feed is shown in
Generally, the catalysts used for the reforming reactions are categorized into two groups:
・ Supported noble metals, and
・ Non-noble transition metals.
Several investigations have been conducted to find the most suitable catalyst for the production of syngas using different processes. There has been extensive research work on steam reforming, catalytic partial oxidation and dry reforming catalysts including rhodium [
The effect of the support has also been investigated in other active metals, and the tendencies are not the same in all cases. Bitter et al. [
Zirconia [
Iron has also been used as a promoter. Park et al. [
Perovskite oxides have also been extensively used as precursors of supported metal catalysts. Perovskites are mixed oxides with a general stoichiometry of ABO3, where A and B can be partially substituted by other metals.
Technology | Advantages | Disadvantages | Developers/Licensors |
---|---|---|---|
POX | Feed stock desulfurization not required | Very high process operating temperature Usually requires oxygen plant | Texaco Inc. and Royal Dutch/Shell |
SMR | Most extensive industrial experience Oxygen not required, lowest process operating temperature Best H2/CO ratio for production of liquid fuels. | Highest air emissions More costly than POX and auto-thermal reformers Recycling of CO and removal of the excess hydrogen by means of membranes | Haldor Topsoe AS, Foster Wheeler Corp, Lurgi AG, International BV, Kinetics Technology and Uhde GmbH |
ATR | Lowest process temperature requirement than POX. Syngas methane content can be tailored by adjusting reformer outlet temperature | Limited commercial experience Usually requires oxygen plant | Lurgi, Haldor Topsoe |
DMR | Green house gas CO2 can be consumed instead of releasing into atmosphere Almost 100% of CO2 conversion | Formation of coke on catalyst. Additional heat is required as the reaction takes place at 873 K | Carbon Sciences |
CSDR | Best H2/CO ratio for production of liquid fuels Coke deposition drastically reduced. | Separation of un-reacted methane from SMR syngas. Project installation cost. | Midrex Process |
TMR | Directly using flue gases, rather than pre separated and purified CO2 from flue gases. Over 95% of methane and 80% CO2 conversion can be achieved | Usually requires oxygen plant. Low H2/CO ratio ratios limit its large-scale application for F-T & MeOH synthesis | Haldor Topsoe AS |
Most of the perovskites studied have a lanthanide and/or alkaline earth metal in the A site, and the active metal in the B site. After reduction, a highly dispersed metal supported in the lanthanide or alkaline earth oxide is obtained [
Perovskite structures of the type CaTiO3, SrTiO3, BaTiO3 and LaAlO3 have been used as supports by [
On conventional reforming catalysts, discrete metal nano crystals (typically 1.15 nm) are dispersed on support particles that are one to several orders of magnitude larger than the supported metal nano particles. However, when the particle sizes of an oxide support are reduced to such an extent that they become comparable to that of the active metal particles, the oxide may deviate dramatically from its function as a conventional catalyst support. Such metal/oxide catalyst with size-comparable metal and oxide nano crystals may be better called a metal/oxide nano composite rather than an “oxide-supported” metal catalyst [
When the sizes of zirconia particles become smaller than 25 nm, the oxide forms nano composite catalysts with size-comparable Ni-metal nano crystals (10 - 15 nm). The nano composite catalysts show extremely stable catalysis, which is in strong contrast with the deactivating Ni catalyst supported on bigger zirconia particles (>25 nm). Energy dispersive analysis of X-rays focused on individual particles showed little contamination between Ni-metal and zirconia nano crystals. This raises the possibility of tailoring the catalytic behavior of oxide-supp- orted metal catalysts by reducing the particle size of oxide to make high performance nano composite catalysts [
The reason for high stability of nanoco mposite Ni/ZrO2 remains unclear. It could be due to the enhancement of oxygen transfer ability of zirconia particles smaller than 25 nm or by formation of nano composite with high percentage of metal/oxide boundary or perimeter CO2, which in turn increase oxidative removal of carbon atoms to produce CO [
Application of the MgO nanocrystals for support of nickel catalyst was also successful and gave promising results for highly active as well as very stable Ni/MgO catalysts for the dry reforming of methane [
Mesoporous materials when used as the support could control the size of nano particles by the diameter of their pores [
Most recently, an innovative steam- and/or CO2-reforming designated as Thermo-Neutral Reforming (TNR) has been introduced by [
By applying the extremely compact size of the TNR system to the successive syngas converters packed newly developed catalysts, highly effective ultra clean fuels such as MeOH, DME, and sulfur-free & non-aromatic high octane number gasoline can be produced effectively with non-expensive costs.
Recent advances in the steam reforming catalyst have been done through the CO2 reforming associated with the CO2 mitigation against the global warming crisis [
・ No coke formation,
・ High sulfur tolerance,
・ Ultra-rapid reaction rate,
・ High-temperature resistance,
・ Low temperature start-up in a very short time,
・ Non toxic, and
・ Low production cost.
This novel catalyst has both catalytic functions of combustion and steam reforming for hydrocarbons, the thermo-neutral reactions (TNR) on the same catalyst surface could be realized [
From the above review we can conclude that each reforming method has its particularities and the preference of one method over another depends on the final application of the syngas produced. If we need maximum hydrogen production e.g. for the case of ammonia synthesis then steam reforming is the traditional choice. On the other hand, if the syngas produced is to be utilized in the production of liquid hydrocarbon fuels then ATR and POX or more recently SCT-CPO reforming would be the proper choice where H2/CO ratio can be adjusted to the required ratio. New comers like dry reforming and tri-reforming will certainly occupy their proper place with the increased climatic awareness where CO2 is utilized as a raw material. Nickel catalysts supported on alumina or silica are the most used catalysts in the reforming of methane because of their low cost compared to noble metals. It must be emphasized that the method of preparation affects the final structure of the catalyst and therefore its activity. Nano catalysts are gaining grounds in the reforming process. Future challenges include the development of better catalysts that have longer life time and enhance conversion at moderate operating
conditions to reduce the operating cost as well as the development of more compact reactors (Process Intensification) e.g. membrane reactors to lower the capital cost.
Salwa A. Ghoneim,Radwa A. El-Salamony,Seham A. El-Temtamy, (2016) Review on Innovative Catalytic Reforming of Natural Gas to Syngas. World Journal of Engineering and Technology,04,116-139. doi: 10.4236/wjet.2016.41011
ATR Auto-thermal Reforming
BFW Boiler Feed Water
CDPOX Combined Dry Reforming and Partial Oxidation
CPOX Catalytic Partial Oxidation
CSDR Combined Steam and Dry Reforming
CMR Combined Methane Reforming
CTL Chemicals to Liquid Fuels
DME Di Methyl Ether
DMR Dry Methane Reforming
F-T Fischer-Tropsch
GHSV Gas Hourly Space Velocity, h−1
GTL Gas-to-Liquid
HR-TEM High Resolution Transmission Electron Microscopy
HT Heat Transfer or Heat Exchange
IGCC Integrated Gasification Combined Cycle
ITM Ion Transport Membrane
KBR Kellogg Brown & Root Company
MCC Methane Catalytic Combustion
MCMR Multi-Channel Membrane Reactor
MTBE Methyl Tertiary-Butyl Ether
POX Partial Oxidation Method
PSA Pressure swing adsorption
RWGS Reverse Water Gas Shift
SCT- CPO Short contact time-catalytic partial oxidation
SMR Steam Methane Reforming
TGA Thermal Gravimetric Analysis
TNR Thermal Neutral Reaction
TMR Tri Reforming
WGS Water Gas Shift
WHSV Weight Hourly Space Velocity cc g−1・h−1
YSZ Yttria-Stabilized Zirconia