A series of Pt–La/B38 catalysts were prepared for low-temperature isomerization of n-dodecane and the effects of La addition on the textural properties, metal dispersion, acid properties, and catalytic performance were investigated.
Microporous and Mesoporous Materials 346 (2022) 112294 Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso Hydro-isomerization of n-dodecane on Pt–La/Beta catalyst for the production of high quality bio-jet fuel: Effect of La addition Il-Ho Choi a, Hye-Jin Lee b, Kyung-Ran Hwang a, * a b Energy Resource Upcycling Research Laboratory, Korea Institute of Energy Research, Daejeon, 34129, Republic of Korea Institute for Advanced Engineering, Yongin, 17180, Republic of Korea A R T I C L E I N F O A B S T R A C T Keywords: Isomerization Pt–La/Beta Jet fuel N-dodecane Pt dispersion A series of Pt–La/B38 catalysts were prepared for low-temperature isomerization of n-dodecane and the effects of La addition on the textural properties, metal dispersion, acid properties, and catalytic performance were investigated La co-impregnated with Pt on B38 significantly reduced the Pt size and notably enhanced the uniformity in Pt size A higher ratio of accessible Pt and medium-strength Brønsted acid sites and a shorter distance between two Pt particles of Pt–La10/B38 resulted in the maximum iso-C12 yield (59.2–56.2%) in the range of 200–250 ◦ C, due to the reasonable arrangement of active sites caused by La loading Introduction An aqueous-phase bio-cured oil separated from the pyrolysis oil of woody biomass contains up to 60% of the carbon in the original biomass [1] The aqueous fraction is composed of various oxygenated organic compounds, mainly small carbonyl compounds such as ketones, alde hydes, and organic acids [2,3] Recently, researchers have begun to valorise carbon contained in aqueous-phase crude oil such as small olefins and aromatics with HZSM-5 via catalytic conversion [1] In line with the growing demand for bio-jet fuel [4], studies to pre pare fuel precursors through C–C bonding reactions (aldol condensa tion) of small oxygenates in the aqueous fraction are also being conducted [5,6] These medium-chain fuel precursors are transformed to liquid biofuel (n-alkanes) through a hydro-deoxygenation process [7] The medium-chain alkanes produced in this manner are suitable for the carbon range of jet fuel, and further conversion into branched alkanes through isomerization is required to obtain high quality bio-jet fuel (Fig A1) For reference, since n-alkanes obtained from oil-based biomass are mainly long-chain hydrocarbons (C16 and C18), hydro-upgrading (hydro-cracking and isomerization) is performed in the last step to obtain high-yield and high-quality jet fuel The catalyst used for hydro-upgrading is a bi-functional catalyst (Pt/HY, Pt–Mg/HY, Pt–Pd/HB, Pt/SAPO-11, etc.) wherein active metal and acid sites coexist and the cracking and isomerization reaction of paraffin occur simulta neously according to the reaction mechanism [8–10] However, unlike the existing hydro-upgrading catalysts suitable for long chain alkanes, more careful catalyst design is required for the isomerization of medium-chain hydrocarbons (C8, C13, etc) obtained through the C–C bonding reactions of small oxygenates This is because, during the isomerization reaction on the bi-functional catalyst, a cracking reaction of the medium-chain alkane is accompanied, thereby lowering the yield of jet-fuel Therefore, in order to obtain a high-yield jet fuel while preserving the carbon number in medium-chain alkanes synthesized from small oxygenates, a catalyst in which isomerization is dominant rather than cracking of the medium-chain alkanes is required In particular, it is important to find a composition with excellent cata lytic performance at low temperatures, since hydro-cracking easily oc curs at high temperatures due to endothermic reactions [11] Many studies have been conducted to improve the yield of isomers by changing the catalyst properties in the isomerization reaction of medium-chain alkanes [11,12] As a result of performing the isomeri zation reaction of n-dodecane with Pt/SAPO-11 prepared under different synthesis condition for SAPO-11 (particle sizes of 65 nm to 4.5 ㎛), it is found that both suitable acidity and suitable particle size of SAPO-11 for shorter diffusion path are closely related to the yield of isomers [12] In the isomerization reaction of n-octane, Ni–Cu/SAPO-11 was prepared to suppress hydrogenolysis of n-alkane [11] Hydro genolysis was inhibited by reducing the active ensemble size by diluting the active metal (Ni) with inactive Cu, resulting in an isomer yield of about 63% at 340 ◦ C Low-temperature isomerization of n-hexadecane was performed using Pt–Pd/HB (Si/Al = 25) with different Pt and Pd ratios Bi-metallic catalysts showed an enhanced metal dispersion (92%) * Corresponding author E-mail address: hkran@kier.re.kr (K.-R Hwang) https://doi.org/10.1016/j.micromeso.2022.112294 Received 22 August 2022; Received in revised form October 2022; Accepted 17 October 2022 Available online 28 October 2022 1387-1811/© 2022 The Authors Published by Elsevier Inc This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/bync-nd/4.0/) I.-H Choi et al Microporous and Mesoporous Materials 346 (2022) 112294 relative to mono-metallic catalysts (54%) and the conversion was also increased along with the metal dispersion (65%–77%) [13] A small amount (0.5 wt%) of rare earth metals (Ce, La, and Re) were loaded on Pt/ZSM-22 to suppress the Pt sintering during reduction treatment since the Pt dispersion is important in the low-temperature isomerization of alkane [14] Ce or La oxides helped to protect the nano-sized Pt metal and induced an electron-deficiency state of Pt However, the Ce-modified Pt/ZSM-22 showed better isomerization performance than the La-modified catalyst due to the strong interaction of a Pt–O–Ce bond Rare earth metal (Ce, La, Nd, and Yb) - exchanged Pt/HB catalysts were also prepared [15,16] The Ce-exchanged HB (0.2–0.8 wt% loading) exhibited higher conversion and selectivity for isomerized products than the parent HB catalyst due to the reducibility of Pt species facilitated by the ion-exchanged Ce [16] On the other hand, in the case of La-exchanged Pt/HB, only a small amount of loading (0.3 wt%) had a slight positive effect on the isomerization performance due to the formation of new Lewis acid sites [15] As such, in the bi-functional catalytic system, the catalytic performance for the isom erization reaction of n-paraffin is greatly affected by the pore size and acid site strength and density [12], the residence time of the olefinic intermediate in the pores [17,18], the metal dispersion (distance be tween metals) [11,13], and the metal/acid balance [17,19], as well as the reaction conditions, and studies are being conducted to increase the degree of isomerization at relatively lower temperatures Nevertheless, it is still necessary to explore catalyst compositions that can maximize the isomer yield while minimizing the cracking reaction, in order to achieve high-yield and high-quality fuel through isomerization of medium-chain alkanes In this work, a series of Pt–La/HB (Beta zeolite, Si/Al = 38) catalysts were prepared for low-temperature isomerization of n-dodecane as a model compound of medium-chain alkane In general, a Pt catalyst impregnated on an acidic support with a low Si/Al ration is more active but less selective for the isomerization reaction However, beta zeolite with a low Si/Al ratio (B38) was selected to increase the conversion of nalkane at relatively low temperatures and La was added on Pt/B38 The textural properties, metal dispersion, and acid properties of the La- loaded catalysts were characterized using various techniques and the accessible metal/acid ratio and an average acid step between two metal sites were discussed to highlight the importance of balancing the accessible metal and acid sites related to conversion and isomer yield Experimental 2.1 Catalyst preparation CP814C (B38) as a powder type beta zeolite was purchased from Zeolyst, and the zeolite was calcined before use at 500 ֠C for h in air As Pt and La precursors, chloroplatinic acid solution (Sigma-Aldrich, wt %) and lanthanum nitrate hexahydrate (Samchun Chem., >98%) were used The catalyst was prepared by the wetness impregnation method using a mixed aqueous solution of Pt and La precursors, followed by calcination at 450 ֠C for h in air To determine the effect of La addition, the loading amount of Pt was fixed at wt%, and the prepared catalysts were denoted as follows: Pt–La’x’/B38, where x is the tentative La content 2.2 Characterization To determine the textural properties of the prepared catalyst, a Brunauer-Emmett-Teller (BET) analysis was conducted by using 3Flex (Micromeritics Co., LTD.) The sample was degassed at 200 ֠C overnight, and was cooled to − 196 ֠C for N2 adsorption The structural property was estimated by an X-ray diffraction analysis (XRD, SmartLab 9kW/Rigaku Co Ltd.) To observe the acidity of the catalyst’s surface, NH3-temper ature programmed desorption (NH3-TPD) and Fourier transform infrared spectroscopy (FTIR) were utilized by using a BELCAT II catalyst analyzer (BELCAT) and a Nicolet iS50+ (Thermo Scientific), respec tively In the case of NH3-TPD, NH3 was adsorbed on the sample at 50 ֠C, and then desorbed with increasing temperature to 800 ֠C Meanwhile, pyridine, employed as a probe molecule in the FTIR analysis, was adsorbed at 100 ֠C, and then desorbed In the desorption profiles of pyridine at below 300 ֠C, two bands overlap around 1445–1444 cm− 1, Fig FE-STEM/TEM and EDS images of the prepared catalysts: (a) Pt/B38, (b) Pt–La2/B38, and (c) Pt–La10/B38 (the yellow arrow in the figure points to a Pt particle) (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.) I.-H Choi et al Microporous and Mesoporous Materials 346 (2022) 112294 corresponding to pyridine interacting with the hydroxyl group and pyridine bonded to a relatively stronger Lewis site, respectively Thus, we chose the pyridine desorption profile of 300 ֠C to confirm the strong Lewis site because the pyridine bonded to the hydroxyl group disappears below 300 ֠C A H2-temperature programmed reduction (H2-TPR) experiment was carried out to evaluate the temperature at which hydrogen consumption for Pt oxides occurred using an AutoChem II (Micromeritics) The contents of Pt in the prepared catalysts were determined by using inductively coupled plasma – optical emission spectroscopy (ICP-OES, OPTIMA7300DV/PerkinElmer), and a CO-pulse chemisorption (BELCAT II catalyst analyzer/BELCAT) was used for measuring the Pt dispersion and size Visual images of the catalysts were obtained by using a field emission-scanning transmission electron mi croscope (FE-S/TEM, HF5000/Hitachi Co Ltd.) equipped with an en ergy dispersive spectrometer (EDS) Before the TEM analysis, the catalysts were reduced at 350 ֠C for h with H2 are summarized in Table The specific surface area and total pore volume decreased with the impregnation of Pt and La on the bare B38 support In particular, an increase in the amount of impregnated La had a greater effect on the reduction of micropore volume than the meso/ macropore volume As a result, the mean pore diameter increased from 2.15 nm to 2.29 nm This reduction in micropores and increase in mean pore diameter are advantageous in terms of reducing the cracking re action of olefinic intermediates, because retention of the intermediate in micropores induces cracking reactions at acid sites The Pt dispersion of the Pt/B38 catalyst was 41.7%, whereas the Pt dispersion increased to more than 60% when impregnated with La on Pt/B38 The XRD patterns of the prepared catalyst are shown in Fig A2 Compared with the XRD pattern of B38, the intensity of the character istic peak of B38 decreased as the loading amount of La on the catalyst increased Also, no characteristic peaks related to La were found even when 12 wt% of La was impregnated on the B38 This indicates that an amorphous lanthanum oxide (LaOx) was formed, which can be confirmed from the TEM images presented later FE-STEM/TEM and EDS images of the prepared catalysts (Pt/B38, Pt–La2/B38, and Pt–La10/B38) are shown in Fig and Fig A3 In the case of Pt/B38 (Fig 1(a) and Fig A3(a)), large Pt particles (approximately, 26–36 nm) are exposed to the external surface of the support, and small size Pt particles are distributed between them Small Pt appears to be present within the pores rather than on the surface of the catalyst particles The low Pt dispersion confirmed by the CO pulse method (Table 1) appears to be due to the large Pt particles exposed to the outside As shown in Fig 1(b) and Fig A3(b), when Pt and a small amount of La were impregnated on B38, large and small Pt particles were also mixed However, it is observed that, unlike Pt/B38, the size of Pt exposed to the outside was drastically reduced (approximately, 6–14 nm) As observed in the EDS mapping of the Pt–La2/B38, Pt is distributed evenly on the support with La It appears that co-impregnated La improves the dispersion of Pt, as shown in Table (Pt dispersion) When 10 wt% of La was co-impregnated with Pt on B38 (Pt–La10/B38), all large-sized Pt particles disappeared and nano-sized Pt particles (~approximately, 3.3 nm) were uniformly distributed (Fig 1(c) and Fig A3(c)) It thus can be seen that as the amount of co-impregnated La increases, the uniformity and dispersion of nano-sized Pt particles appear to increase However, unlike the STEM/TEM images, the Pt dispersion (63.7–68.4%) measured by the CO pulse (Table 1) was similar regardless of the amount of La loading for the Pt–La5~12/B38 catalysts This appears to be due to the Pt size gradually decreasing when the amount of La loading exceeds a certain amount (about wt%), whereas as the catalyst surface is covered with lanthanum, the number of externally exposed Pt (accessible Pt) decreases little by little However, they still show higher dispersions (more than about 63.7%) than Pt/B38 As shown in the STEM image (Figs 1(c-3)), amorphous LaOx was observed, which is consistent with the XRD result where La-related peaks did not appear (Fig A2) Nevertheless, as shown in both EDS mapping (Figs 1(c-4)) and line-EDS (Fig A3(c)), La and Pt are well distributed throughout H2-TPR was employed to further confirm the reduction in size of Pt particles by La addition to Pt/B38 (Fig A4) For Pt/B38, the reduction peaks centered at 80 ◦ C and 355 ◦ C were attributed to the reduction of PtOx particles loaded on the external surface and dispersed in the in ternal pores of B38, respectively [19] The reduction temperature for PtOx loaded on the external surface of B38 was gradually shifted to higher temperatures (above 200 ◦ C) as the loading amount of La in creases This indicates that the size of PtOx particles loaded on the external surface of the support becomes smaller, which is accordant with the results of the FE-S/TEM analysis However, excessive loading of La (12 wt%) reduced the amount of Pt species exposed on the surface, and thus the hydrogen consumption was relatively reduced La thus appears to play a role in preventing agglomeration of co-impregnated Pt and facilitating uniform nano-size dispersion Table summarizes acid properties of the prepared catalysts, based 2.3 Hydro-isomerization reaction Low-temperature hydro-isomerization was conducted with low temperature and atmospheric pressure in a continuous fixed bed reac tion system The prepared catalyst (400 mg) was inserted into the tubular reactor (quartz, I.D mm), and then the reactor was mounted on a furnace Hydrogen (Special Gas Co Ltd., 99.999%) was injected with a flow of 100 ml/min into the reaction system The reactor was heated to 350 ֠C for the catalyst’s reduction, and then the hydroisomerization was progressed at 160–340 ֠C The temperature devia tion was maintained below 1% As a model compound, n-dodecane (Sigma-Aldrich, >99%) was employed and pumped into the reaction system with 5.85 h− weight hourly space velocity (WHSV) by an HPLC pump (Optos 1HM, Eldex) The liquid sample was collected by using a cold trap, and the trap was cooled by ice to condense the products derived from the reactor The collected sample was analyzed by a gas chromatograph (GC, Simadzu Co Ltd./GC-2010 plus) equipped with a frame ionization de tector (FID) and mass spectroscopy (MS, Simadzu Co Ltd./GCMSQP2010 SE) Both instruments used the same RTX-5 column (30 m × 0.25 mm x 0.25 μm) and oven program (held to 50 ֠C for min, heated to 220 ֠C (10 ֠C/min and held for min), and further heated to 280 ֠C (15 ֠C/ and held for min)) To quantitatively measure unconverted ndodecane and isomerized products (iso-C12), n-pentadecane (Aldrich, >99%) was used as an internal standard, and the response factor of isomerized products was assumed to be the same with n-dodecane The terminologies were defined by the following equations: Conversion (%) = the amount of converted n − dodecane (g) × 100 the amount of injected n − dodecane (g) iso − HC12 yield (%) = the amount of produced iso − C12 (g) × 100 the amount of injected n − C12 (g) iso − HC12 selectivity (%) = the amount of produced iso − C12 (g) × 100 the amount of converted n − C12 (g) iso − HC12 in product (g) iso − HC12/n − HC ratio ( − ) = , and 12 n − HC12 in product (g) nPt/ nBA ( − ) = ( ) the amount of exposed Pt metal mmol/g ( ) the amount of medium − strength Brønsted acid sites mmol/g Results and discussion 3.1 Catalyst characteristics The textural properties and Pt dispersion of the prepared catalysts I.-H Choi et al Microporous and Mesoporous Materials 346 (2022) 112294 Table Textural properties and metal dispersion of the prepared catalysts Catalysts BET surface area (m2/g) a B38 Pt/B38 Pt–La2/B38 Pt–La5/B38 Pt–La7/B38 Pt–La10/B38 Pt–La12/B38 a b c d e b Micro Meso 680.4 608.9 561.6 523.5 517.8 464.1 457.3 102.5 83.4 80.5 83.3 86.0 73.3 79.3 Total pore volume (cm3/g) b Macro Total c a b Micro Meso 0.4 0.7 0.7 0.7 0.3 0.6 0.6 680.9 606.9 579.6 539.3 529.6 467.2 465.9 0.212 0.196 0.178 0.165 0.163 0.146 0.141 0.114 0.098 0.095 0.093 0.102 0.093 0.095 b Mean pore diameterd (nm) Pt dispersione (%) 2.12 2.15 2.16 2.21 2.20 2.28 2.29 – 41.7 60.7 65.9 63.8 68.4 63.7 c Macro Total 0.010 0.015 0.015 0.015 0.008 0.014 0.014 0.341 0.301 0.288 0.275 0.272 0.241 0.243 calculated from T-plot data calculated from BJH desorption data calculated from specific BET data calculated from BJH adsorption data, and calculated from CO pulse (accessible Pt) and ICP data (Pt content) Fig Results of hydro-isomerization of n-dodecane using B38, Pt/B38 and Pt–La10/B38 catalysts (WHSV = 5.85/h) on the results of NH3-TPD and pyridine-FTIR (Fig A5) When wt% of La was loaded on Pt/B38, the total acid sites increased However, as the amount of La was further increased, the amount of acid sites decreased slightly because the amorphous lanthanum oxides covered the acid sites (Fig and A3) However, they still have more acid sites than B38 or Pt/ B38 In addition, the Brønsted acid sites related to the skeleton isom erization of the reactant also decreased according to the La loading, while Lewis acid sites were generated due to the formation of amor phous LaOx Considering the ratio of accessible Pt and Brønsted acid sites (nPt/nBA), Pt–La2~10/B38 had a higher nPt/nBA value (0.117–0.132) than that of Pt/B38 (0.076), but there was not a significant difference among the values It is noteworthy that although nPt/nBA shows similar values, the size of accessible Pt becomes smaller as the amount of loaded La increases (Fig 1, Fig A3, and Fig A4) 3.2 Low-temperature isomerization of n-dodecane The desired isomerization reaction entails dehydrogenation of nalkane on Pt site, skeleton rearrangement of olefinic intermediate on active acid sites, and hydrogenation of iso-olefin on Pt site occurring continuously and smoothly, while preserving the number of carbons in the reactant Fig shows the conversion and the selectivity of iso4 I.-H Choi et al Microporous and Mesoporous Materials 346 (2022) 112294 Table Acid properties measured with NH3-TPD and pyridine-FTIR of the prepared catalysts Catalysts B38 Pt/B38 Pt–La2/B38 Pt–La5/B38 Pt–La7/B38 Pt–La10/B38 Pt–La12/B38 a b c Acid site (mmol/g) Weak Medium Strong Total 0.955 0.933 1.428 1.246 1.146 1.116 1.104 0.358 0.442 0.614 0.618 0.597 0.579 0.547 0.193 0.248 0.4 0.299 0.281 0.273 0.147 1.506 1.623 2.442 2.163 2.024 1.968 1.798 B/L ratioa (− ) Brønsted acid siteb (mmol/g) Lewis acid siteb (mmol/g) nPt/nBAc (− ) 1.48 1.40 0.89 0.74 0.74 0.65 0.80 1.12 1.15 0.92 0.87 0.92 0.88 0.99 0.76 0.88 1.04 1.18 1.25 1.36 1.23 – 0.076 0.123 0.132 0.118 0.117 0.103 the ratio of Brønsted acid (B) and Lewis acid (L) of pyridine-FTIR profile calculated from NH3-TPD data and the ratio of B and L of pyridine-FTIR profile the ratio of total amount of exposed Pt sites to the total amount of medium-strength B site dodecane (a), the yield of iso-dodecane (b), and the distribution of product (c and d) for B38, Pt/B38, Pt–La10/B38, and La10/B38 B83 and La10/B38 were inactive for isomerization of n-dodecane at reaction temperature below 280 ◦ C, but n-dodecane started to be converted above 300 ◦ C where a severe cracking reaction was predominant, and thus the liquid product was hardly recovered In the case of Pt/B38, ndodecane stared to be converted at 180 ◦ C and showed 100% conversion at 240 ◦ C However, most cracked hydrocarbons with less than five carbons and gases were generated in the high conversion section (Fig (c)), and as the conversion increased according to the reaction temper ature, the selectivity of iso-C12 fell inversely As a result, the maximum yield (22.9%) of the desired iso-C12 was obtained at 200 ◦ C with a conversion of about 30% (Fig 2(b)) For Pt–La10/B38, the conversion was delayed by about 20 ◦ C compared to that of Pt/B38, but the selec tivity of iso-C12 was maintained high in the range of 200–250 ◦ C The selectivity of iso-C12 at 260 ◦ C, which showed 100% conversion, decreased sharply, and the maximum iso-C12 yield (59.2–56.2%) was thus obtained in the range of 240–250 ◦ C (Fig 2(b)) As shown in Fig (c), distributions (mono-branched and multi-branched isomers and cracked hydrocarbons) in the product varied according to the conver sion of n-dodecane over the bi-functional catalyst n-dodecane was mainly transformed into cracked hydrocarbons over B38 acid catalyst In the case of Pt/B38, isomers were mainly produced at low conversion (less than about 30%), but as the conversion increased, cracked products became the dominant species due to their secondary transformation This appears to be due to poor hydrogenation resulting from low nPt/ nBA (0.076) This trend was similar when La was co-impregnated with Pt on B38, but the conversion at which the secondary transformation began to appear in Pt–La10/B38 was delayed by about two times (at about 60% conversion) For comparison, hydro-isomerization of ndodecane was performed using a Pt/SAPO-11 which is one of the wellknown catalysts for hydro-isomerization (not shown here) The con version of 64.9% and the isomer yield of 52.1% were obtained at 300 ◦ C Thus, Pt–La10/B38 shows better catalytic performance even at 250 ◦ C than Pt/SAPO-11 that have been studied recently The ratio of cracked product and isomer (C/I ratio) and the ratio of multi- and mono-branched isomers (multi/mono ratio) are provided in Fig 2(d) Both C/I and multi/mono ratios of Pt–La10/B38 were lower than those of Pt/B38 This means that skeleton isomerization and hy drogenation of n-dodecane are balanced on the Pt–La/B38 catalyst In conclusion, as shown in Table 2, it can be seen that the high nPt/nBA (0.117) of Pt–La10/B38 is suitable for producing iso-C12 under the present reaction conditions, where the carbon number of the feed (ndodecane) is preserved while minimizing the cracking reaction in the range of low reaction temperature The average number of active acid sites that one n-dodecane mole cule encountered during the catalytic reaction, nas, was estimated based on the initial product distribution to observe the characteristics of the diffusion path of olefinic intermediates between two Pt metal sites and the results are summarized in Table [18] B38 was converted at high temperature (above 280 ◦ C in Fig 2(a)) because there was no metal Table The initial weight distribution in the product and estimated average number of active acid steps involved in the n-C12 transformation between two Pt sites Catalysts Conversion (%) Monobranched C12 (wt fraction) Multibranched C12 (wt fraction) Cracked products (wt fraction) naas B38 Pt/B38 Pt–La10/ B38 6.17 5.59 2.29 0.06 0.71 0.93 0.03 0.29 0.07 0.91 0.00 0.00 3.78 1.43 1.11 a nas = (mono-branched C12 × 1) + (multi-branched C12 × 2.5)+(cracked products × 4) [8,18] active site for dehydro/hydrogenation, and mostly cracked products were produced, traveling approximately 3.8 acid steps When Pt was impregnated on B38, isomers were mainly generated in the initial re action, and the number of active acid sites involved in the trans formation was greatly reduced In the case of Pt–La10/38, the nas value was close to 1.1 This is considered a result of the reduced the distance between nano-sized Pt particles, as can be seen from TEM images and Pt dispersion This is consistent with the results of previous studies [18] However, it is difficult to find a significant difference between nas values estimated from the initial reaction of two catalysts (Pt/B38 and Pt–La10/B38) This is because the possibility that inactive acid sites exist under the operating conditions (180 and 200 ◦ C) cannot be excluded This is confirmed by observing the change of nas values ac cording to the reaction temperature, shown in Fig A6 As the conversion of n-dodecane increased, the nas values of two bifunctional catalysts increased This indicates that the increase of the reaction temperature causes more acid sites to become active, and also increases the diffu sivity of the olefinic intermediates However, it is clear that Pt–La10/B38 still shows lower nas values than Pt/B38 at similar con versions, and the gap between the two values increases as the temper ature (conversion) increases This means that in the Pt–La10/B38 catalyst with well dispersed nano-sized Pt particles, even if the reaction temperature rises, the average number of active acid sites that the in termediates encounters while traveling through the surface of the cat alysts is small due to the short distance between Pt particles Fig shows the results of hydro-isomerization of n-dodecane ac cording to the La content impregnated on the Pt/B38 at 250 ◦ C Although the conversion was close to 100% on Pt/B38 at 250 ◦ C, the recovered iso-C12 yield was very low due to the predominant cracking reaction (Fig A7) As the amount of La loading increased, the conversion of dodecane decreased, but the selectivity and yield of the desired iso-C12 tended to increase The maximum yield of iso-C12 was obtained in the 10% La impregnated catalyst The reason for the change in catalytic properties (conversion, selectivity and yield) in the Pt–La series catalysts even with similar nPt/ nBA values is (1) an increase of uniformity of nano-sized Pt and (2) the I.-H Choi et al Microporous and Mesoporous Materials 346 (2022) 112294 smaller distance between two Pt particles caused by La loading, result ing in predominant hydrogenation of the olefinic intermediates That is, the optimal loading of La reduce the distance between Pt particles and enhances the intimacy between the uniformly distributed nano-sized Pt and the active acid sites A further increase of the La loading (more than 12 wt%) resulted in lowered catalytic performance, likely due to the coverage of the Brønsted acid and Pt sites by LaOx with Lewis acid sites, as discussed in the results of FE-S/TEM and H2-TPR, consistent with a previous study showing that the conversion is related to the externally exposed Pt over the catalyst [19] For the Pt–La2~10/B38 catalysts, the ratio of iso-C12/n-C12 was greater than 2.1 Note that the ratio decreases as the content of La increases because uncovered n-dodecane remains Fig shows the time-on-stream stability of Pt–La10/B38 in hydroisomerization of n-dodecane Initial conversion and isomer yield were 86% and 57%, respectively, but the isomer yield gradually decreased (46%) until h of time-on-stream After shutting down the reaction system, the catalyst was in-situ cleaned with acetone without any other regeneration process In the subsequent reaction, the conversion and isomer yield were maintained within 75–80% and 55–60%, respectively, which means that the catalyst can be regenerated only by washing with acetone Based on the above results, the hydro-isomerization reaction over the bifunctional catalysts is schematically drawn in Fig The mechanism of hydro-isomerization on the bi-functional catalyst has been well documented in several studies [13] In general, the n-alkane is dehy drogenated to the alkene intermediates on the Pt active site and the intermediates are protonated and isomerized on the Brønsted acid sites, and then hydrogenated on the nearby Pt active site to form a desired iso-alkane Meanwhile, the low nPt/nBA value and the diffusion limi tation of the intermediates in the microporous channels of acid supports increases the contact opportunity and the contact time with the acid sites, resulting in further cracking to obtain unwanted cracking prod ucts That is, a proper arrangement of metal and acid sites is very important in bi-functional catalysts, as well as the textural structure of the catalysts For Pt–La10/B38, the size of Pt was very small and uni form Such uniformly distributed nano-sized Pt particles (~approxi mately, 3.3 nm) give the reactant many opportunities for dehydro/hydrogenation reactions, resulting in the production of many olefinic intermediates at the same time The intermediates undergo skeletal rearrangement at an adjacent acid site and then hydrogenate at a nearby Pt site to form isomers In addition, the La loading reduces the volume of micropores, thereby suppressing the cracking reaction that occurs from the diffusion limitation of the intermediates Fig The time-on-stream stability of Pt–La10/B38 in hydro-isomerization of n-dodecane (250 ◦ C and WHSV = 5.85/h) Conclusion A series of Pt–La/B38 catalysts were prepared for low-temperature isomerization of n-dodecane and the effect of La addition on the cata lytic performance (conversion, selectivity and yield) was investigated Based on the results of CO pulse chemisorption, FE-S/TEM images, and a H2-TPR analysis, La (10 wt%) co-impregnation in Pt/B38 resulted in an increase of the Pt dispersion (41.7%–68.4%) Moreover, the size of Pt loaded on the external surface of B38 was significantly reduced from approximately 26–36 nm–~3.3 nm and the uniformity in Pt size was notably enhanced La thus appears to play a role in preventing agglomeration of co-loaded Pt and facilitating uniform nano-size Pt dispersion Pt/B38 showed good activity at relatively low reaction temperature (100% conversion at 220 ◦ C), but most cracked hydrocar bons with less than five carbons and gases were generated in the high conversion section, resulting in a maximum yield, 22.9%, for the desired iso-C12 Meanwhile, for Pt–La10/B38, the conversion was delayed by about 20 ◦ C compared to that of Pt/B38, but the selectivity of iso-C12 was maintained high in a range of 200–250 ◦ C, resulting in the maximum isoC12 yield (59.2–56.2%) Both the C/I and multi/mono ratios of Pt–La10/ B38 were lower than those of Pt/B38, indicating that skeleton isomeri zation and hydrogenation of n-dodecane are balanced on the Pt–La/B38 catalyst In conclusion, the desirable arrangement of active sites with higher nPt/nBA (0.1777) and lower nas (1.11) caused by La loading in the Pt–La/B38 catalyst enhances the catalytic performance for lowtemperature isomerization of n-dodecane Funding A National Research Foundation of Korea grant funded by the Korea government CRediT authorship contribution statement Il-Ho Choi: Writing – review & editing, Writing – original draft, Methodology, Investigation, Formal analysis, Conceptualization HyeJin Lee: Methodology, Formal analysis Kyung-Ran Hwang: Writing – review & editing, Supervision, Project administration, Investigation, Conceptualization Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence Fig Results of hydro-isomerization of n-dodecane using Pt/B38 and a series of Pt–La/B38 catalysts (250 ◦ C and WHSV = 5.85/h) I.-H Choi et al Microporous and 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for highly efficient aldol condensation of furfural with acetone, Catal Commun 166 (2022), 106451, https://doi.org/ 10.1016/j.catcom.2022.106451 ... prepared for low-temperature isomerization of n-dodecane and the effect of La addition on the cata lytic performance (conversion, selectivity and yield) was investigated Based on the results of CO... conversion) For comparison, hydro-isomerization of ndodecane was performed using a Pt/SAPO-11 which is one of the wellknown catalysts for hydro-isomerization (not shown here) The con version of 64.9%... shows the results of hydro-isomerization of n-dodecane ac cording to the La content impregnated on the Pt/B38 at 250 ◦ C Although the conversion was close to 100% on Pt/B38 at 250 ◦ C, the recovered