Suppression Of Coke Formation Research Articles

코크 생성 억제를 위한 이산화탄소 건식 개질 반응기의 최적 설계

지구 온난화가 가속화됨에 따라 온실가스 감축이 보다 중요해졌다. 이산화탄소 건식 개질은 온실가스인 CO2와 CH4를 활용하여 부가가치가 높은 물질인 CO와 H2를 얻을 수 있는 유망한 온실가스 감축 기술이다. 그러나 이 반응이 일어나는 반응기의 운전 중에 심각한 코킹 문제가 발생할 수 있다. 이산화탄소 개질반응은 매우 강한 흡열반응이기 때문에 반응기 입구 근처에서 반응 온도가 많이 떨어지면서 코크 생성을 야기시킨다. 이러한 문제를 해결하기 위해서는 코크 생성이 잘 일어나지 않는 온도영역에서 반응이 일어나도록 하는 것이 중요하다. 본 연구에서는 새로운 촉매 배열 방법을 이용하여 반응기 전 구간이 코크 생성이 잘 일어나지 않는 온도 영역 내에서 유지되도록 하는 설계 방법을 제안하였다. 이 설계 방법은 연료 유량, 촉매 밀도, 구간 별 출구 온도를 최적화 변수로 하여 주어진 전환율에 대하여 반응기 길이를 최소화 할 수 있는 최적화 문제를 풀도록 하여 반응기를 최적화한다.

Manganese silicate based redox catalysts for greener ethylene production via chemical looping – oxidative dehydrogenation of ethane

The current study investigates manganese silicate based redox catalysts for ethane to ethylene conversion in a chemical looping oxidative dehydrogenation (CL-ODH) process. Facilitated by a two-step cyclic redox scheme, CL-ODH has the potential to overcome the drawbacks of traditional steam cracking including high energy consumption, coke formation, and significant CO2 and NOx emissions. In CL-ODH, lattice oxygen in manganese silicate based redox catalysts is used to combust the hydrogen formed from ethane dehydrogenation, enhancing ethylene formation and suppressing coke formation. The oxygen-deprived redox catalyst is subsequently regenerated with air, releasing heat to balance the overall heat requirement. The key to this process is an efficient redox catalyst with high selectivity and facile oxygen transport. In this study, redox catalysts with combined manganese and silica phases were tested. We report that redox catalysts with high manganese content are more effective for CL-ODH due to their higher oxygen capacity at reaction temperatures. Sodium tungstate was used as a promoter due to its effectiveness to suppress COx formation. Among the redox catalysts investigated, sodium tungstate promoted (1.7 wt.% Na) manganese silicate (Mn:Si molar ratio = 70:30) was the most effective, showing an ethylene selectivity of 82.6% and yield of 63.3%. Temperature programmed reaction (TPR) experiments indicate that the sodium tungstate promoter inhibits ethane activation on the surface of the redox catalyst and is selective towards hydrogen combustion. XPS analysis indicates that the manganese silicate redox catalysts have a smaller amount of near surface Mn4+ than previously studied manganese containing redox catalysts, leading to higher ethylene selectivity on the un-promoted redox catalysts. XPS also indicates that the reduction of the un-promoted redox catalysts leads to the consumption of silica and formation of inosilicate species. ASPEN Plus® simulations of the CL-ODH scheme using manganese silicate based redox catalysts indicate significant energy and emissions savings compared to traditional steam cracking: the overall energy consumption for ethylene production can potentially be reduced by 89% using the manganese silicate based redox catalyst in the CL-ODH process. Resulting from the significant energy savings, CO2/NOx emissions can be reduced by nearly one order of magnitude when compared to traditional steam cracking.

Kinetics of Steam Gasification of Glucose as a Biomass Surrogate over Ni/Ce–Mesoporous Al2O3 in a Fluidized Bed Reactor

This study reports the kinetics of steam gasification of glucose as a biomass surrogate over a new Ni(x)/Ce-doped Al2O3 (x = 5, 10, 15, and 20 wt %) catalyst in a fluidized bed reactor. The presence of ceria plus successive nickel impregnation helped in conserving the catalyst’s high surface area (i.e., 102 m2/g at 20 wt % nickel loading). Incorporation of ceria dopant suppressed coke formation during steam gasification of 15 wt % glucose in the fluidized bed reactor at 650 °C and 1 atm in the order Ni(20) < Ni(15) < Ni(10) < Ni(5)/Ce-doped Al2O3. The detailed kinetic model comprises reactant adsorption, surface reaction, and product desorption steps, involving the water gas shift reaction (WGS), steam reforming of methane (SRM), and reverse dry reforming of methane (RDRM). Ni(20)/Ce-doped Al2O3 with the best performance in terms of syngas production, and the least tendency for coking, was used for the kinetic studies (for T = 550–700 °C and t = 5–25 s). The results of the model simulation indicate that t...

Relationship between Coking Behavior in Hydrocarbon Fuel Pyrolysis and Surface Roughness

The pyrolysis of hydrocarbon fuels can give rise to the formation of coke on metal substrate surfaces. Until now, there are few research reports about how the nature of these surfaces affects the formation of coke, especially the effect of surface roughness. A series of samples of different surface roughnesses was obtained by mechanical polishing, and the coking property with changed surface roughness was evaluated by cyclohexane cracking under 1 atm at 730–810 °C. The coke obtained was then analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and temperature-programmed oxidation (TPO). The results showed that reducing the surface roughness can effectively decrease the amount of coke in different ranges of cracking temperatures and cracking times, especially in high-temperature ranges (above 770 °C). The polishing process reduced the metal catalytic activity of coking to inhibit coke formation without changing the mechanism of cyclohexane cracking. Su...

Catalytic Steam Reforming of Heavy Oilstock: Review Paper

Deterioration of the quality of oilstock makes it an urgent problem to use non-traditional hydrocarbon materials (heavy oil, bitumen, residues etc.). Processing of heavy oilstock (HOS) needs new methods that would be effective for the yields of light fractions, suppression of coke formation, and saturation of the liquid products with hydrogen. At the same time, expenses of HOS extraction and transportation are several times as high as those of light and middle oils that makes it necessary to minimize the capital and operational costs for the process. The review paper integrates for the first time the results of the studies of catalytic steam reforming of HOS as a potential alternative of the traditional processes for HOS upgrading based on decreasing the carbon content (thermal cracking, visbreaking, catalytic cracking) or on the saturation of liquid products with hydrogen (hydrocracking). Under discussion are main distinctions of the process from HOS upgrading with water (hydropyrolysis in sub- or supercritical water) as well as specific features of the catalytic steam cracking as dependent on the process parameters and catalysttype and putative mechanisms of the participation of water in the process.

Co‐processing bio‐oil in the refinery for drop‐in biofuels via fluid catalytic cracking

Pyrolysis oil from lignocellulosic biomass (bio‐oil) is a promising renewable energy carrier that can be utilized for the production of second‐generation drop‐in biofuels. Co‐processing bio‐oil with petroleum feeds in existing refinery processes, such as fluid catalytic cracking (FCC), has been proposed as a cost‐effective way of transitioning to the production of such biofuels without the need for significant capital‐intensive investments. Several routes are available for the production of bio‐oil, such as fast pyrolysis of biomass (raw bio‐oil), catalytic fast pyrolysis of biomass (catalytic pyrolysis oil, CPO), and fast pyrolysis of biomass followed by hydrogenation of the produced bio‐oil (hydrodeoxygenated oil, HDO). Research has shown that co‐processing raw bio‐oil is challenging but it can be carried out after adoption of appropriate reactor modifications in the commercial scale. A significant body of work has also focused on the co‐processing of HDO and CPO, and has demonstrated that these types of bio‐oil can be co‐processed with less operational issues. Co‐processing bio‐oil results in a liquid hydrocarbon product that contains only a small amount of oxygenates from bio‐oil. A noticeable increase in coke formation is also observed when bio‐oil is introduced in the FCC feed. However, this increase is lower than what would be expected from the conversion of the pure bio‐oil fraction. This has been attributed to the presence of the petroleum feed, which has a beneficial synergistic effect on the cracking of bio‐oil due to hydrogen donation reactions that inhibit coke formation and promote the conversion of the oxygenates to liquid hydrocarbons.This article is categorized under: Energy and Climate &gt; Climate and Environment Bioenergy &gt; Systems and Infrastructure Bioenergy &gt; Economics and Policy

Dry Reforming of Methane Using a Nickel Membrane Reactor

Dry reforming is a very interesting process for synthesis gas generation from CH 4 and CO 2 but suffers from low hydrogen yields due to the reverse water–gas shift reaction (WGS). For this reason, membranes are often used for hydrogen separation, which in turn leads to coke formation at the process temperatures suitable for the membranes. To avoid these problems, this work shows the possibility of using nickel self-supported membranes for hydrogen separation at a temperature of 800 ∘ C. The higher temperature effectively suppresses coke formation. The paper features the analysis of the dry reforming reaction in a nickel membrane reactor without additional catalyst. The measurement campaign targeted coke formation and conversion of the methane feedstock. The nickel approximately 50% without hydrogen separation. The hydrogen removal led to an increase in methane conversion to 60–90%.

Multi-metal catalysts for slurry-phase hydrocracking of coal-tar vacuum residue: Impact of inherent inorganic minerals

Multi-metal catalysts for slurry-phase hydrocracking of coal-tar vacuum residue were investigated. The multi-metal catalysts system consisted of pyrrhotite (Fe1−xS) transformed from inherent inorganic minerals in coal-tar vacuum residue and mixed molybdenum (Mo)–nickel (Ni) sulfide catalysts. The inherent inorganic minerals included iron oxide (hematite-Fe2O3, goethite-FeO(OH)) and other minerals. The formed pyrrhotite (Fe1−xS) was acting as an active phase for hydrocracking. Mo naphthenate and Ni naphthenate were used as precursors to the dispersed Mo–Ni sulfide catalysts. The multi-metal sulfide catalysts were confirmed to form and well dispersed across the toluene insoluble sample by XRD, XPS and EDS analysis during hydrocracking. Comparative reaction tests revealed that the inherent inorganic minerals, as Mo–Ni catalyst carrier and coke carrier, enhanced the dispersion of Mo–Ni catalysts and induced less coke formation. Compared with only the Mo–Ni catalysts or inherent inorganic minerals, the multi-metal catalysts system promoted the thermal decomposition of CTVR feedstock at a low temperature, and suppressed coke formation, increased the liquid yield and improved hydrodeheteroatom at a high temperature, which resulted from the synergistic effects between the Mo–Ni sulfides and the inherent inorganic minerals.

Numerical study of catalytic steam reforming of aviation kerosene at supercritical pressures

A new two-dimensional numerical model is proposed for supercritical catalytic steam reforming of Chinese aviation kerosene No. 3 (RP-3) in order to suppress the coke formation during regenerative cooling of scramjet engines. A well-established wall catalytic steam reforming mechanism is used together with the newly proposed coke formation models to account for the coke formation during wall catalytic steam reforming reaction of RP-3. This wall catalytic steam reforming and coking model is coupled with computational fluid dynamics (CFD) codes to provide information of the flow field variables in the mini-channel reactor. The model is validated against experimental results. The effects of water content, pressure and inlet flow velocity on the wall catalytic reforming of RP-3, particularly on the coke formation, are then studied and analyzed. The simulation results show that higher water content and higher pressure can effectively suppress coke formation and increase the conversion of RP-3. The increase of inlet flow velocity, however, can reduce coke deposits but results in low conversion of RP-3.

Rapid evaluation of coke resistance in catalysts for methane reforming using low steam-to-carbon ratio

The formation and subsequent accumulation of coke is one of the major reasons for the catalyst deactivation in methane reforming reaction. Although the investigation of coke-resistant catalysts is closely related to their long-term stability of given catalysts, it takes a long time to quantitatively measure the amount of carbon deposition on catalysts under normal reaction operational conditions. To overcome this problem, we used the steam deficient reaction condition, i.e. a low steam-to-carbon ratio (S/C) of 0.5 to accelerate the carbon deposition on catalysts. In this condition, the base catalyst of 10wt.% Ni/alumina rapidly lost its catalytic activity, indicating fast coke deposition. However, adding proper additives, such as Ru among various precious metals (Ru, Rh, Pt, and Pd) and alkaline earth metals (Mg, Ca, Sr, and Ba) with the appropriate loading (5wt.%) effectively suppressed coke formation. The optimized catalyst composition is 0.5wt.% Ru/5wt.% Mg/10wt.% Ni/alumina, which displayed coke resistance in the long-term stability test of steam methane reforming and 40h test of dry reforming of methane. These experimental results indicate that the method developed in this study is useful for the rapid evaluation of given catalysts for their coke resistance.

Operando Spectroscopy of the Gas-Phase Aldol Condensation of Propanal over Solid Base Catalysts

The gas-phase aldol condensation of propanal, taken as model for the aldehyde components in bio-oils, has been studied with a combined operando set-up allowing to perform FT-IR & UV–Vis diffuse reflectance spectroscopy (DRS) with on-line mass spectrometry (MS). The selected solid base catalysts, a cesium-exchanged X zeolite (Cs-X), a calcium hydroxyapatite (Ca-HA) and two alkaline metal-grafted ultrastable Y (Na- and Rb-USY) zeolites, were characterized ex-situ by FT-IR after CO (CO-IR) and pyridine (Py-IR) adsorption and subsequent desorption. The combined operando spectroscopy study shows that alkaline metal-grafted USY zeolites are the most selective catalysts towards aldol dimer product formation, while the hydroxyapatite was more selective for successive aldol condensation reactions. For Na-USY and Rb-USY, the C–C coupling seems to be the rate-determining step during the surface reaction, which is the limiting stage of the overall catalytic process. In contrast, for the two more basic catalysts, i.e., Cs-X and Ca-HA desorption is limiting the overall catalytic process. Furthermore, the combined operando FT-IR & UV–Vis DRS methodology allowed monitoring the formation of carbonaceous deposits as a function of reaction time. In particular, for Cs-X and Ca-HA the rapid formation of carbonaceous deposits was observed consisting of (poly-)aromatics and highly conjugated structures, respectively. The physicochemical properties of Ca-HA with strong basic sites and moderate acidity limit its deactivation despite the observed coke formation. On the other hand, both USY catalysts were more efficient in suppressing coke formation likely due to the moderate strength of their active sites.

Methanol conversion over ZSM-12, ZSM-22 and EU-1 zeolites: from DME to hydrocarbons production

Conversion of methanol to dimethyl ether (DME) and hydrocarbons was investigatedover zeolites with several 1-dimensional channel systems: ZSM-12, ZSM-22 and EU-1. The effect of reaction temperature, contact time and Time-On-Stream towards methanol conversion and products selectivity was investigated. It was found that ZSM-22 zeolite exhibits the best performances during conversion of methanol to DME (temperature range 180–240°C) as consequence of the particular shape selectivity that inhibits coke formation and deactivation. On the contrary, when formation of hydrocarbons is desired (temperature up to 320°C), ZSM-12 shows the highest activity in terms of light olefin yield with the highest C3/C2 ratio. The low selectivity towards C2 formation can be associated to the absence of both di- and tri-methyl benzenes formed during the reaction because when these species were detected, a higher ethylene productivity was observed lowering the C3/C2 ratio on the reactor out-stream.

Tailored Ce- and Zr-doped Ni/hydrotalcite materials for superior sorption-enhanced steam methane reforming

Multi-functional hybrid materials are attractive for producing high-purity hydrogen (H2) via catalytic steam reforming coupled with low temperature adsorptive separation of CO2. In this work, modified Ni/hydrotalcite-like (HTlc) hybrid materials promoted with Ce and Zr species were synthesized and applied for the sorption-enhanced steam methane reforming process (or SESMR). The promotion with Ce and Zr resulted in strongly basic sites for CO2 adsorption, and hence, improved H2 production. Especially, the Ce-promoted hybrid material (Ce-HM1) exhibited the highest adsorption capacity (1.41 mol CO2/kg sorbent), producing 97.1 mol% H2 at T = 723 K, P = 0.1 MPa, S/C = 4.5 mol/mol and gas hourly space velocity or GHSV = 3600 mL/(g h); the breakthrough time was 1 h. High surface area and basicity of the promoted materials inhibited coke formation and undesired reactions. In addition to the improved catalytic activity and adsorption characteristics, these materials were stable and easily regenerable. Multi-cycle durability tests revealed that both the promoted materials Ce-HM1 and Zr-HM1 remained stable for up to 13 and 17 cycles. In contrast, the unpromoted hybrid material (HM1) was stable for 9 cycles only. Thus, promotion with Ce and Zr was beneficial for producing pure H2.

Role of Pt during hydrodeoxygenation of biomass pyrolysis vapors over Pt/HBEA

1.3wt% Pt/HBEA and HBEA were studied as catalysts for the hydrodeoxygenation of pine pyrolysis vapors at 500°C. Both catalysts showed high initial conversion of oxygenated pyrolysis products into aromatic hydrocarbons, while Pt/HBEA showed higher stability in terms of hydrocarbon productivity and deferred breakthrough of oxygenated compounds. Among 1-, 2- and 3-ring aromatic hydrocarbons, Pt/HBEA had a significantly higher selectivity than HBEA towards unalkylated aromatics (e.g., benzene) as compared to the corresponding alkylated aromatics (e.g., toluene and xylene). Additionally, Pt addition to HBEA decreased coke deposition and improved resistance to pore and acid site blockage as determined by TPO, N2 physisorption, and NH3 TPD. The ability of Pt to promote cleavage and hydrogenation of methoxy and methyl groups was observed by increased methane production over Pt/HBEA relative to HBEA. A progressive decrease in the methane production over Pt/HBEA correlated with deactivation in terms of reduced benzene formation, breakthrough of oxygenated products, and increased formation of polynuclear aromatics and their degree of substitution, which indicate coke formation. The increased methane yield and suppressed coke formation with the addition of Pt is attributed to hydrogen spillover, through which hydrogen activated on Pt can subsequently migrate to the HBEA support to reverse the coke-forming hydrogen abstraction reaction.

Ethanol Steam Reforming for Renewable Hydrogen Production over La-modified Tio2 Catalyst

In recent years, ethanol steam reforming (ESR) has received considerable attention as a promising route for cleaner H2 production. This process could be industrially advantageous, ideally yielding 6 moles of H2 per mole of ethanol reacted. The major drawbacks of the process are the endothermic nature of the reaction and presence of CO2 in the product. At low temperatures (below 500 °C), side reactions that yield alternative products such as acetic acid, acetaldehyde and ethylene are favoured. Besides promoting ESR, higher temperatures make the process costly for an industrial development while promoting CO, CO2 and coke formation, which is the main cause of catalyst deactivation. In this study, a series of La-loaded TiO2 catalysts were prepared by an impregnation-co-precipitation method, La being a well-known inhibitor of CO and CO2 formation. Catalytic ethanol steam reforming was conducted in a tubular fixed bed reactor operated at 1 atm, 500 °C and an ethanol/water molar feed ratio of 10:1. The influence of La-loading on inhibiting coke formation and selectivity towards hydrogen formation by ethanol steam reforming has been investigated. The catalytic performance of La-loaded TiO2 catalyst was found to be considerably higher when compared to the pure TiO2. At 10 % La loading, ethanol conversion of ~27.5 % was achieved with a H2 mole fraction of 0.53. Significant amounts of valuable products such as CH4 and C2H4 were also detected in the product mixture. More importantly, CO was not detected over La-loaded TiO2 catalyst, which confirmed its ability for minimizing coke formation. This development has confirmed improved efficiency of La/TiO2 catalyst toward renewable hydrogen production.

Effects of secondary mesoporosity and zeolite crystallinity on catalyst deactivation of ZSM-5 in propanal conversion

Cooperative effects of secondary mesoporosity and zeolite crystallinity on the deactivation of ZSM-5 were investigated during propanal conversion. Varied secondary mesoporosities were introduced into a commercial ZSM-5 by alkaline desilication using solutions with different NaOH concentrations (0.1–0.5 M). The results showed that the mesoporosity gradually increased with the concentration of NaOH, while the intrinsic zeolitic microporosity decreased. This indicated that the alkaline desilication for mesopore generation is a destructive technique that sacrifices the zeolite crystallinity. In propanal conversion, ZSM-5 showed a longer catalyst lifetime as the external surface area increased (or as the zeolite framework thickness decreased) in the mild desilication regime (NaOH concentration ≤ 0.3 M). The enhanced catalyst lifetime could be attributed to the facilitated diffusion of coke precursors out of the zeolite structure. However, when the zeolite crystallinity or microporosity of ZSM-5 was decreased too much from excessively severe alkaline treatments (NaOH concentration > 0.3 M), deactivation of the catalyst became again faster. The result indicates that the crystallinity or the microporosity of ZSM-5 is also important in suppressing coke formation. This is in line with earlier reports showing that coke formation itself is a shape-selective reaction and significantly inhibited in the constrained space of the unique 10-membered micropore channels of ZSM-5. The present results imply that the generation of large mesoporosity (enhancing the diffusion of coke precursors) while keeping the zeolite crystallinity intact (suppressing coke formation by shape-selectivity) is highly desirable for designing a zeolite catalyst with an enhanced catalyst lifetime.

Tri-reforming as a process of CO2utilization and a novel concept of energy storage in chemical products

Methane tri-reforming process is a combination of three reactions: steam methane reforming (SRM), dry methane reforming (DRM), and partial oxidation of methane (POM). The first two reactions have endothermic character, while the POM is the exothermic reaction, which allows to obtain the energy necessary for the other two processes in situ. CH4 reacts with H2O, CO2, O2, and synthesis gas is produced with desired H2/CO ratios (1.5 – 2.0). The presence of H2O and O2 in the reaction environment can positively influence the stability of the used catalyst, by the inhibition of coke formation.

Effects of H2O Addition on Oil Sand Bitumen Cracking Using a CeO2–ZrO2–Al2O3–FeOx Catalyst

The behavior of a CeO2–ZrO2–Al2O3–FeOx catalyst typically employed during heavy oil decomposition was investigated in conjunction with the addition of H2O, as a means of improving the upgrading activity and suppressing coke formation on the catalyst. The upgrading of oil sand bitumen diluted with benzene was examined with this catalyst at various FH2O/Fbitumen ratios [where FH2O is the water flow rate (g h–1) and Fbitumen is the bitumen feedstock flow rate (g h–1)] in a fixed-bed flow-type reactor. Under optimal conditions (FH2O/Fbitumen equal to approximately 20) and at a reaction temperature of 693 K, effective catalytic decomposition of the bitumen was observed with the lighter component (gas oil and vacuum gas oil) yield reaching 71 mol % C. In addition, the formation of coke on the catalyst was decreased to less than 14 mol % C. Analyses using quadrupole mass spectrometry determined that this catalyst upgrades the heavy oil through oxidation reactions, in which the lattice oxygen of the iron oxide is...

Steam reforming of n-dodecane over K2Ti2O5-added Ni-alumina and Ni-zirconia (YSZ) catalysts

The steam reforming of n-dodecane over 35 wt% Ni supported on alumina (Ni-Al2O3) and yttrium-stabilized zirconia (Ni-YSZ) at 800 °C for 10 h with a steam-to-carbon ratio of 3 was tested in the presence and absence of 10 wt% of K2Ti2O5 (KTO) particles. The suppression of coke formation by KTO was investigated using various characterizations, including BET, TPO, TGA, TEM, and EELS. After the addition of 10 wt% of KTO particles by ball milling, Ni-YSZ exhibited stable performance with negligible coke formation at space velocities of less than 20,000 h−1. The addition of KTO to Ni-Al2O3 did not yield any improvements because the majority of Ni particles in alumina pores are not directly in contact with the KTO phase. The dispersion of finely divided KTO particles on the surfaces of both Ni and the support effectively suppressed coke formation by steam gasification of the deposited coke into CO and H2. First, the gradual accumulation of coke during the course of the reaction deactivated the Ni sites, which presented activity for the steam reforming of methane. The Ni and acidic sites, which were effective for the hydrogenolysis of n-dodecane to methane and ethylene (or ethane in the presence of KTO), were eventually deactivated. An overall reaction pathway was then proposed based on the results.

Promotional Effects of In on Non-Oxidative Methane Transformation Over Mo-ZSM-5

We present a new class of catalysts, InMo-ZSM-5, which can be prepared by indium impregnation of Mo-ZSM-5. The incorporation of indium dramatically decreases coke formation during methane dehydroaromatization. The benzene and C2 hydrocarbons selectivity among total hydrocarbons over InMo-ZSM-5 remains comparable to that of Mo-ZSM-5 despite reduced methane conversion due to decreased coke formation. We found 1 wt% indium to be optimal loading for reducing coke selectivity to half that of Mo-ZSM-5. Characterization methods were not helpful in discerning the interaction of In with Mo but experiments with bimetallic 1In2Mo-ZSM-5 and mechanical mixture 1In+2Mo-ZSM-5 suggest that In and Mo need to be in close proximity to suppress coke formation. This is supported by temperature programmed reduction experiments which show that In incorporation leads to lower Mo reduction temperature in In2Mo-ZMS-5.