Al Migration Research Articles

A novel formation mechanism: One-step synthesis of high-purity MAX phase bulk via enlarged reaction depth

The synthesis of high purity MAX phase bulk still faces a big challenge. In this study, we fabricated 98 vol% MAX phase bulk doped with Al2O3 nanoparticles through spark plasma sintering by using larger size TixAl1-x powders (particle size ∼100 μm) for the first time, in which 91 vol% Ti2AlN was the dominant component. The phase transition mechanism for Ti2AlN was deeply revealed by both experiments and theoretical calculations. Ti proportion of TixAl1-x powders played a key role in the formation of Ti2AlN, and increasing Ti proportion leaded to higher content of Ti2AlN. Both Al migration from TixAl1-x and TiN nanotwins generated by N vacancies could enlarge the reaction depth, resulting in fully transformation of larger size reactants and thus high purity MAX phase as obtained. Further, the transition model for the synthesis of Ti2AlN was accordingly proposed, which contained three stages and was additionally verified by experimental observations.

Characterization of electromigration-induced short-range stress development in Al(0.25 at. % Cu) conductor line

Scanning x-ray microbeam topography and fluorescence experiments were conducted in situ to study the electromigration behavior of a 0.5 μm thick, 10 μm wide, and 200 μm long Al(0.25 at. % Cu) conductor line with 1.5 μm-thick SiO2 passivation on a single crystal Si substrate. The strain sensitivity of x-ray topography measurement allowed detailed examination of the electromigration-induced stress distribution and evolution in the conductor line in response to the depletion of Cu solute early in the electromigration process. Upon electromigration at 0.4 MA/cm2 and 303 °C, a short-range stress gradient was quickly induced by Al migration in the Cu-depleted cathode region to counteract further Al flow. The stress gradient was fully developed during the 5.3 h incubation time, extending over the critical Blech length of about 66 μm from the cathode end. Plastic deformation then occurred at the downstream end of the Cu-depleted region. The preferential electromigration of Cu did not cause detectable stress change outside the Cu-depleted region, except for the significant stress development from the Al2Cu precipitation at the anode end which appeared to initiate the fracture in the passivation. Preliminary finite difference modeling was undertaken to simulate the experimental observations, from which important parameters dictating electromigration in Al(Cu) line were extracted: an apparent effective valence of −5.6 and −1.9 for Cu and Al in Al(Cu), respectively, and a critical Cu concentration of 0.16 at. % above which Al grain boundary diffusion is effectively blocked.

Assessment of the stability of LTA zeolites under natural gas drying TSA conditions

The main features in cationic LTA zeolites that are likely to impact its potential hydrothermal stability are interconnected. The Al content and the compensating cation play an important role in the water adsorption but their influence on the zeolite performance in thermal cycles is yet to be understood. In this study, four LTA zeolite samples were synthetized with distinct Si/Al ratios in sodium and potassium forms. They underwent a Premature Aging Protocol (PAP) that took into account the operating conditions typically found in temperature swing adsorption processes. The Si/Al ratio per se did not impact in the crystallinity upon aging, but the presence of a high amount of potassium cations (Si/Al = 1) led to the amorphization of the zeolite structure. The results from XPS and NMR techniques indicate the Al migration from the outer surface to the inner cages occurs upon aging. Chemical analysis by XRF and ICP-OES associated with 27Al NMR analysis reveal that the presence of EFAl is particularly significant in the sample with the largest Si/Al ratio (5) and is correlated to a much larger C deposition upon aging. TG/DTG and TPD-NH3 experiments suggest that acid sites in the zeolite structures act as a double-edged sword, by enhancing water adsorption while also leading to carbon accumulation. CO2 isotherms at 0 ºC reveal the reduction of the microporosity after aging, whereas the Al content is proportional to the water adsorption uptake, particularly at low pressures (below 10 mbar). The material with an intermediate Si/Al ratio and in Na-form (LTAc-SiAl2-Na) combines excellent hydrothermal stability with a high-water affinity and uptake.

Study on Al migration, microstructure and hardness in fusion zone of Al-Si coated press-hardened steel by various laser powers

In this paper, the influence of Al distribution in the fusion zone (FZ) on microstructures and properties of welded joints was studied under 13 different laser powers (300 W→3000 W). The results show that Al can quickly accumulate at the upper surface of the FZ and the fusion line. Due to the stirring action of the beam and the dilution of the molten pool metal, Al becomes gradually uniform with the increase of laser power. This work guides the welding process parameters of lap welding the second layer steel plate to obtain uniform weld. In addition, with the decrease of Al content, the microstructure and hardness of the FZ change as follows: Al-based solid solution (Al > 60.2 wt%, 80 ∼ 120 HV) →Fe-Al intermetallic compound (IMC) (10 wt% < Al < 60.2 wt%, 340 ∼ 980 HV) →Fe-based solid solution (Al < 10 wt%, 350 ∼ 530 HV). Therefore, this work revealed the relationship between the distribution-microstructure-hardness of Al and gave the possible microstructures and properties database of Fe/Al welding joints.

Migration of Framework Aluminum and Tunable Acidity in Y Zeolite by Post-treatment

Two industrial Y zeolites were treated sequentially by steaming and citric acid to investigate the Al migration and acidity of the modified Y zeolites. Even though the two parent Y zeolites displayed similar properties including crystallinity, Si/Al ratio, and textural structure, they showed different acidic and textural properties upon identical post-treatments by steaming and citric acid due to the different Al migration rules, resulting in their different activity and cracking ability in the methylcyclohexane transformation. Steaming treatment performed the prominent dealumination, leading to the increase of the framework Si/Al ratio from ca. 2.5 to ca. 5.0 and the formation of extra-framework Al species. During steaming treatment, the dealumination is related with the transformation from Al(IVb) to Al(V). The following citric acid leaching hardly removed the framework Al but removed the extra-framework Al species that existed in the form of Al(V) readily and some residual Na+ ions. The remaining framework-associated Al species are related to the generation of Lewis acid sites.

Multi-electron reaction and fast Al ion diffusion of δ-MnO2 cathode materials in rechargeable aluminum batteries via first-principle calculations

Rechargeable aluminum batteries with multi-electron reaction have a high theoretical capacity for next generation of energy storage devices. However, the diffusion mechanism and intrinsic property of Al insertion into MnO2 are not clear. Hence, based on the first-principles calculations, key influencing factors of slow Al-ions diffusion are narrow pathways, unstable Al-O bonds and Mn3+ type polaron have been identified by investigating four types of δ-MnO2 (O3, O’3, P2 and T1). Although Al insert into δ-MnO2 leads to a decrease in the spacing of the Mn-Mn layer, P2 type MnO2 keeps the long (spacious pathways) and stable (2.007–2.030 Å) Al-O bonds resulting in the lower energy barrier of Al diffusion of 0.56 eV. By eliminated the influence of Mn3+ (low concentration of Al insertion), the energy barrier of Al migration achieves 0.19 eV in P2 type, confirming the obviously effect of Mn3+ polaron. On the contrary, although the T1 type MnO2 has the sluggish of Al-ions diffusion, the larger interlayer spacing of Mn-Mn layer, causing by H2O could assist Al-ions diffusion. Furthermore, it is worth to notice that the multilayer δ-MnO2 achieves multi-electron reaction of 3|e|. Considering the requirement of high energy density, the average voltage of P2 (1.76 V) is not an obstacle for application as cathode in RABs. These discover suggest that layered MnO2 should keep more P2-type structure in the synthesis of materials and increase the interlayer spacing of Mn-Mn layer for providing technical support of RABs in large-scale energy storage.

Influence of catalyst pelletization on propane dehydrogenation over hierarchical MFI zeolite supported with platinum-yttrium nanoparticles

Platinum-yttrium (PtY) nanoparticles supported on a siliceous form of mesoporous MFI zeolite (MZ) were recently found to exhibit excellent catalytic performance in propane dehydrogenation (PDH). Herein, potential shaping of the PtY/MZ catalyst is investigated from the laboratory-synthesized powder form into industrially preferable pellets. The MZ zeolite powder was synthesized using multi-ammonium surfactants as a structure-directing agent and then pelletized in a hydraulic press by itself or with inorganic binders (i.e., pseudoboehmite, fumed silica, or hydrotalcite). As a part of the sequential pelletization process, pressing was followed by a high-temperature treatment (923 K). Addition of 20 wt% pseudoboehmite resulted in the highest mechanical strength without a significant loss of the initial zeolite mesoporosity. The pseudoboehmite-bound pellet also showed high catalytic activity and longevity in PDH application when simultaneously impregnated with 1 wt% Pt [Pt(NH3)4(NO3)2] and 1 wt% Y [Y(NO3)2·6H2O]. Notwithstanding the observed high propane conversion, the pseudoboehmite-bound catalyst produced an unsatisfactory result of low propylene selectivity (∼60%). Image analyses of HAADF-STEM EDS and solid-state 31P NMR spectroscopic data suggest that such findings could be attributed to Al migration from pseudoboehmite onto zeolite regime during the phase transformation of pseudoboehmite in the shaping process. Alternatively, the uses of non-acidic binders, such as fumed silica and hydrotalcite binders were also demonstrated. The silica-bound catalyst yielded high propane conversion with high propylene selectivity although mechanical strengths of the pellet were compromised to a moderate level.

Direct Observation of Al Migration Enhancement by Changing the Al and N Source Relative Position in the Molecular Beam Epitaxy of AlGaN Nanowires

Aluminum (Al)-containing nitrides, including AlN, AlScN, and AlGaN, are emerging material platforms for future-generation photonic, electronic, ferroelectric, and multifunctional semiconductor devices. Nonetheless, the low Al migration mobility in a nitrogen environment is a notorious hindrance to obtaining high-quality Al-containing nitride epilayers. This is particularly the case for the epitaxy of Al-containing nitrides with radio frequency (RF) plasma-assisted molecular beam epitaxy (MBE), due to the use of relatively low substrate temperatures. As such, various approaches have been employed in promoting Al migration such as metal-modulated epitaxy (MME). Despite the progress, the effect of the relative position of the Al and N sources on the Al migration mobility has remained unclear. In this study, we show that MBE-grown AlGaN nanowires can be an effective probe to examine the effect of the Al and N source relative position on the Al migration mobility and demonstrate clearly that Al adatoms appear to be more mobile from the Al source that is far away from the N source, compared to those from the Al source that is near the N source. This study therefore can potentially impact the development of emerging Al-containing semiconductor devices by MBE. Moreover, the demonstrated correlated Al source dependent morphological and optical properties of AlGaN nanowires can naturally help the development of AlGaN-nanowire-based UV light-emitting diodes (LEDs) and lasers.

Probing resistive switching in HfO2/Al2O3 bilayer oxides using in-situ transmission electron microscopy

In this work, we investigate the resistive switching in hafnium dioxide (HfO2) and aluminum oxide (Al2O3) bilayered stacks using in-situ transmission electron microscopy and X-ray energy dispersive spectroscopy. Conductance of the HfO2/Al2O3 stack changes gradually upon electrical stressing which is related to the formation of extended nanoscale physical defects at the HfO2/Al2O3 interface and the migration and re-crystallization of Al into the oxide bulk. The results suggest two competing physical mechanisms including the redistribution of oxygen ions and the migration of Al species from the Al electrode during the switching process. While the HfO2/Al2O3 bilayered stack appears to be a good candidate for RRAM technology, the low diffusion barrier of the active Al electrode causes severe Al migration in the bi-layered oxides leading to the device to fail in resetting, and thereby, largely limiting the overall switching performance and material reliability.

Theoretical insights into the behaviors of sodium and aluminum on the cathode titanium diboride surfaces

Density functional theory calculations were adopted to systematically investigate the adsorption and diffusion behaviors of sodium and aluminum over TiB2 surfaces or in TiB2 crystal to characterize the interaction mechanism between sodium and TiB2 cathode in aluminum reduction cells. Results suggest that Na and Al will stably adsorbe on the low-index TiB2 (0 0 0 1) surface, and the presence of vacant defects can significantly strengthen this adsorption. The migration of Na and Al over pristine TiB2 is anisotropic, with the largest energy barrier of 0.024/0.32 eV for Na and 0.28/1.57 eV for Al over Ti/B-terminated surfaces. The Ti vacancy in Ti-terminated surface is more effective to hinder Na and Al migration with the large diffusion barriers of 0.36 eV for Na and 2.07 eV for Al. Specially, for the B-terminated surface, B vacancy will promote the Na and Al diffusion with the lower barriers. Additionally, it is difficult for Na and Al to form interstitial defects and diffuse in covalent TiB2 crystal. Given these results, compared to graphite cathode, the sodium prefers to deposit on TiB2 surface, and the strong interaction between sodium and TiB2 promotes the early process of sodium penetration. On the other hand, the smoother landscape for Na diffusion on the TiB2 surface suggests the decreased stability of aluminum liquid, so that the current efficiency of aluminum reduction cell will decrease.

Thermodynamically driven Al migration across ultrathin Ag layered electrodes without thermal loading

The use of metallic dopants and seeds as wetting inducers for synthesizing ultrathin Ag layers on chemically heterogeneous oxides has been criticized for inducing nonnegligible degradation in the optoelectrical properties of Ag. This report presents a series of experimental and numerical investigations that reveal a substantial migration of atomic Al across ultrathin (<10 nm) Ag layered electrodes at room temperature, which provides a reliable means of minimizing optoelectrical degradation. Experimental evidence revealed the substantial segregation of atomic Al along the topmost surfaces of Ag geometries, followed by the migration of the majority of the Al atoms beyond the Ag domains into the upper SiOx and Au layers in the SiOx/Ag/SiOx and SiOx/Ag/Au configurations, respectively. The Al atoms incorporated into the SiOx layer were completely oxidized. Numerical calculations indicated that the Al migration across the Ag geometries was driven toward simultaneous decreases in the formation energy and surface free energy of Ag. The findings elucidate the Al migration across Ag domains at room temperature and refute the existing convictions that only support the oxidation-driven and thermal loading-driven migration mechanisms.

Revisiting γ-alumina surface models through the topotactic transformation of boehmite surfaces

The rational understanding of γ-alumina (γ-Al2O3) supported catalysts requires an ever more improved atomic scale determination of the support’s surface properties. By using density functional theory (DFT) calculations, we show how the structural and energetic surface properties of alumina crystallites intrinsically depend on its synthesis pathway. Considering the case study of the topotactic transformation of boehmite (γ-AlOOH) into γ-Al2O3 taking place during calcination, we propose a methodology to mimic this pathway by reconstructing relevant slabs of boehmite into γ-alumina slabs following 3 steps: dehydration, contraction/translation and Al migration into spinel or non-spinel sites. On the one hand, we confirm the reliability of some earlier 100, 110 and 111 surface structures determined by standard bulk cleavage approach. Moreover, we find new γ-alumina surfaces harboring Brønsted acid sites (BAS) and Lewis acid sites (LAS) with specific local structures. More strikingly, we find that the basal 110b surface of alumina inherited from the (010) basal surface of boehmite, exhibits a larger number of isolated µ2-OH groups than the lateral 110l surface. For the lateral 110l (respectively 111) orientation, four (respectively three) thermodynamically competing surfaces are identified, including models earlier proposed. These results are induced by finite size and morphology effects during the topotactic transformation of boehmite crystallites. Thanks to a thorough comparative analysis of morphology and nature of BAS and LAS as a function of thermal treatment and water pressure for each surface, we identify coherent chemical families of surfaces across the main crystallographic orientations. These features open the door to a better differentiation of the reactivity of the basal alumina surfaces from the lateral ones.

Effect of an Al2O3-based binder on the structure of extruded Fe-ZSM-5

The effect of an alumina-based binder on the structure of a commercial Fe-ZSM-5 catalyst has been investigated. Several ex-situ characterization techniques were used to show that the binder in the catalyst formulation allows obtaining a material that possesses improved features in terms of Fe species dispersion, framework Al content and acidity. UV–Vis and X-ray absorption spectroscopy showed that the extent of Fe agglomeration in the extruded catalyst was significantly lower compared to that in the catalyst without binder. 27Al and 29Si-MAS NMR spectroscopy demonstrated a remarkable difference in terms of framework Al migration. NH3-TPD experiments corroborated the NMR results suggesting a retention of Brønsted acidity in the extruded catalyst. We tentatively propose that by providing extra-framework Al species prior to the treatment at elevated temperature, the binder hinders the framework Al dislodgment and Fe agglomeration during calcination.

Improved Performance of GaN-Based Light-Emitting Diodes Grown on Si (111) Substrates with NH3 Growth Interruption.

We demonstrate the highly efficient, GaN-based, multiple-quantum-well light-emitting diodes (LEDs) grown on Si (111) substrates embedded with the AlN buffer layer using NH3 growth interruption. Analysis of the materials by the X-ray diffraction omega scan and transmission electron microscopy revealed a remarkable improvement in the crystalline quality of the GaN layer with the AlN buffer layer using NH3 growth interruption. This improvement originated from the decreased dislocation densities and coalescence-related defects of the GaN layer that arose from the increased Al migration time. The photoluminescence peak positions and Raman spectra indicate that the internal tensile strain of the GaN layer is effectively relaxed without generating cracks. The LEDs embedded with an AlN buffer layer using NH3 growth interruption at 300 mA exhibited 40.9% higher light output power than that of the reference LED embedded with the AlN buffer layer without NH3 growth interruption. These high performances are attributed to an increased radiative recombination rate owing to the low defect density and strain relaxation in the GaN epilayer.

Repeatable room-temperature self-healing memory device based on gelatin films

Flexible gelatin resistive memory device exhibits a high ON/OFF ratio of over 106. Moreover, the bended gelatin resistive memory device can efficiently heal at room temperature without any external stimulus. This self-healing behavior of gelatin resistive memory device was demonstrated based on the metal chelating ligand. Al ions migrating from the top radio frequency Al electrode contributed to the construction of the metal chelating ligand. The carboxylates of gelatin can form multi-dentate coordination compounds with Al ions, which can restore the memory properties of the gelatin resistive memory device. Thus, Al ion migration from the top Al electrodes plays an important role in self-healing capability. The effect of Al ions on the self-healing mechanism was investigated by using secondary ion mass spectrometry, which is useful for the characterization of Al migration from the top electrode. This capability for restoring the electrical properties of gelatin memory device is desirable for flexible electronics and represents a major step toward self-healable bioelectronics.

Potential Health Threat Due To Migration of Lead And Aluminum into Food Cooked with Recycled Metal And Alloy Pots

Abstract Objectives Artisanal cooking pots constructed with recycled aluminum and scrapped car body parts are widely used in the developing world for large scale cooking of food for ceremonies, roadside sells and small-scale food processing. Assessment of the potential health risks of pots fabricated with recycled metal/alloy is the objective of this work Methods Three food stuffs; rice, beans and tomato, and five pots; new aluminum pot (NAP), pitted aluminum pot (PAP), artisan aluminum pot (AAP), stainless steel pot (SSP) and artisan alloy pot (AAY) were used to conduct the study. Each pot was used to cook and store each food item for 0, 12 and 24 h. This mimics the usual style of overnight keeping of cooked food inside these pots. Metal contents of the cooked and stored foods were determined with a spectrophotometer and estimate of health risk was calculated based on the tolerable limits specified by the European Food Safety Authority (EFSA) in 2008.. Specific Release Limit (SRL) of metals based on ALARA principles for food contact material (FCM) was also referenced (Council of Europe, 2013). Results Lead migration into cooked food occurred most (4.32 ± 0.18 mg/kg) in AAY pot and least (0.13 ± 0.05 mg/kg) in SSP while Al migration occurred most in AAP. The mean quantities of Al and Pb ions released by all the pots except SSP into cooked food were above the tolerable limits (Pb = 0.01 mg/kg food; Al = 0.1 mg/kg food). In all cases, metal ion migration increased with increase in food/pot contact time. The average range of Pb content in the food samples were 0.03 to 00.75 mg/kg, 0.23 to 2.63 mg/kg, and 0.84 to 4.19 mg/kg for the raw, cooked and after 24 h storage, respectively. In terms of SRL, AAY and AAP were least favored. Irrespective of pot type used, tomato had the highest level of metal ion content followed by beans and then rice. The work demonstrates that the problem of Pb and Al leaching into cooked food correlates with the type of cooking pot, contact time between food and pot as well as the nature of the foodstuff. Conclusions We conclude that artisanal cooking pots as FCM release Al and Pb ions at potentially toxic levels that poses health risks to the population. Stainless steel surface is suggested as better FCM at all levels of food processing. Our results support the need for countries in the developing world to ban the use of artisanal (uncoated) metal/alloy as FCM. Funding Sources This research was self sponsored.

A facile way to improve zeolite Y-based catalysts' properties and performance in the isobutane-butene alkylation reaction.

Different amounts of SiO2 were added to the Al2O3 binders to investigate the binder effect on zeolite Y-based catalysts. The added SiO2 improved the mesopore volume and acidity of the catalysts. Characterization results showed that the catalysts' acid amount increased with increasing the SiO2 amount in the binder, which achieved maximum value when 12% SiO2 was added to the binder. The doped SiO2 in Al2O3 binders improved the Al2O3 phase transformation temperature, which is crucial for Al species to break out of the phase energy and migrate into the zeolite. The lifetime of catalyst Y-Al2O3-12SiO2 is 3.7 times higher than that of Y-Al2O3-0SiO2, and the selectivity of the target products simultaneously improved by 7 percentage point. This work should bring some inspiration to the design and application of zeolite-based catalysts.

Recycling of scrap metal into artisanal cookware

TPS 721: Low and middle income countries: e-waste, occupational health, Exhibition Hall, Ground floor, August 27, 2019, 3:00 PM - 4:30 PM Background: In South Africa, the use of artisanal cookware made from the recycling of scrap metal is widespread. However, the potential of metal exposure from the use of such cookware has not been investigated. The aim of the study was to determine the risk of metal exposure posed by artisanal cookware available in South Africa to end users. Methods: Twenty cookware samples were purchased from across South Africa. Aluminum and silicon concentrations were determined using XRF and the total content of 18 elements (Ag, As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb, Se, Sn, V and Zn) were determined with ICP-MS. To investigate the leaching of metals, artisanal cookware pieces were boiled in a 3% acetic acid solution over a 2-hour period and each experiment was repeated three times. Post leaching, secondary electron images were obtained with a JEOL Field Emission Electron Probe Microanalyzer. Results: The total aluminum (Al) content ranged from 67% to 93%. Silicon was the second most abundant element with a mean of 13.8 %. The mean Al migration of 509 mg L-1 was over 100 times the maximum permissible level allowed for cookware. Lead was detected in all samples with numerous samples highlighting cause for concern. Cadmium and mercury were detected in all pots across all three migrations. However the levels were low (highest levels detected were 1.6 ug L-1 and 0.26 ug L-1 respectively). Transmission electron microscopy revealed dramatic change in surface structure after leaching of cookware. Conclusion: Public awareness on multi-metal exposure and related risks from the use of artisanal cookware should be a public health priority in relevant settings.

Recycling of scrap metal into artisanal cookware in the informal sector: A public health threat from multi metal exposure in South Africa

Recycling of scrap metal into artisanal cookware is widespread in poorly resourced countries. The aim of the study was to determine the risk of metal exposure from the use of artisanal cookware available in South Africa. Twenty cookware samples were purchased from local manufacturers and informal traders across South Africa. Aluminum and silicon concentrations were determined using XRF and the total content of 18 elements (Ag, As, Ba, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb, Se, Sn, V and Zn) were evaluated using ICPMS. Leaching of metals from cut pieces of cookware over a 2-h period of boiling in a 3% acetic acid solution was repeated 3 times and revealed multi-metal migration that was compared to EU maximum permissible levels. The mean Al migration of 509 mg L−1 was over 100 times the EU maximum permissible level allowed for cookware. Lead was detected in all samples with 11 (55%), 12 (60%) and 9 (45%) of samples being over the maximum EU permissible level (10 μg Pb L−1) for 1st, 2nd and 3rd migrations respectively. The mean As migration concentrations in the first leaching event ranged from 0.23 to 24.1 μg L−1 with four pots (20%) over the maximum EU permissible limit for As (2 μg L−1). Notably, all four pots were well below the maximum EU permissible As limit by the 3rd migration. Cadmium and mercury were detected in each pot across all three migrations however the levels were relatively low. Transmission electron microscopy revealed dramatic changes in surface structure after leaching of cookware.

Chemical Imaging of the Binder‐Dependent Coke Formation in Zeolite‐Based Catalyst Bodies During the Transalkylation of Aromatics

AbstractThe choice of binder material, added to a zeolite‐based catalyst body, can significantly influence the catalyst performance during a reaction, i. e. its deactivation and selectivity. In this work the influence of the binder in catalyst extrudates on the formation of hydrocarbon deposits was explored during the transalkylation of toluene with 1,2,4‐trimethylbenzene (1,2,4‐TMB). Using in situ UV‐vis micro‐spectroscopy and ex situ confocal fluorescence microscopy approach, coke species were revealed to predominantly form on the rim of zeolite crystals within Al2O3‐bound extrudates. It was found that this was due to Al migration between the zeolite crystals and the Al2O3‐binder creating additional acid sites near the zeolite external surface. In contrast, minimal isomerization of 1,2,4‐TMB in the SiO2‐bound extrudate allowed greater access to the zeolite internal pore network, creating a more homogeneous coke distribution throughout the zeolite crystals.