Supported Pd Catalysts Research Articles

Reaction pathways for the HDO of guaiacol over supported Pd catalysts: Effect of support type in the deoxygenation of hydroxyl and methoxy groups

The effect of support type (SiO2, CeO2, ZrO2, TiO2, Nb2O5) on the removal of the different oxygenated functional groups (hydroxyl and methoxy) was investigated in the hydrodeoxygenation (HDO) of guaiacol over supported Pd catalysts at 573 K and atmospheric pressure. The product distribution depended on the support type, and three main reaction pathways were proposed: demethoxylation, demethylation and dehydroxylation. Demethoxylation yielding phenol was the dominant reaction pathway over all catalysts with only a minor contribution from the demethylation reaction taking place. However, significant dehydroxylation reaction was still observed for the catalysts having Pd supported on ZrO2, TiO2 and Nb2O5. Further conversion of phenol to cylohexanone was favored over SiO2 and CeO2-based catalysts, while benzene was only detected over ZrO2, TiO2 and Nb2O5, which is due to the presence of oxophilic cations. DRIFTS measurements were carried out to evaluate the adsorption mode and strength of guaiacol on the catalyst surface. The functional groups involved in adsorption of guaiacol included both hydroxyl and methoxy groups. At the reaction conditions, the hydroxyl group is strongly adsorbed to the catalyst surface and may block the catalytic sites, thus inhibiting further conversion of phenol and resulting in lower deoxygenation rates.

Performance of carbon-modified Pd/SBA-15 catalyst for 2-ethylanthraquinone hydrogenation

Abstract Silica SBA-15 without removal of template P123 was calcined in an inert atmosphere and the carbon-modified SBA-15 thus obtained was used as the support of Pd catalyst for the hydrogenation of 2-ethylanthraquinone (EAQ). The effects of extraction times of P123 in SBA-15 with water prior to inert calcination and calcination temperature on the structure and catalytic performance of Pd catalyst were studied. The results of elemental analysis, X-ray diffraction, X-ray photoelectron spectroscopy, inductively coupled plasma, Fourier transform infrared spectroscopy, Raman spectra, water contact angle measurement, N2 adsorption-desorption, transmission electron microscopy and energy dispersive X-ray mapping showed that carbon content of catalysts varied in the range of 3.4 % and 1.1 % with increasing extraction times from 0 to 6 due to the decrease in the residual amount of P123 in uncalcined SBA-15. With rising calcination temperature, the occurrence state of carbon in catalysts was converted from amorphism into graphite. The Pd catalyst supported on SBA-15 extracted for 3 times and calcined at 650 °C had 2.0 % carbon, and exhibited the highest activity (0.37 molH2·gPd−1·min−1) and selectivity (98.9 %). This is due to the presence of appropriate amount of carbon, which provided a relatively high hydrophobicity without significantly reducing the specific surface area and pore size of SBA-15 support. The high hydrophobicity benefits the adsorption of EAQ from the working solution to the surface of catalyst.

Simultaneous utilization of electro-generated O2 and H2 for H2O2 production: An upgrade of the Pd-catalytic electro-Fenton process for pollutants degradation

• Pd/Activated carbon/stainless steel mesh (PACSS) hybrid cathode was fabricated. • H 2 and O 2 from water electrolysis were both utilized by PACSS cathode for H 2 O 2 generation. • PACSS cathode can support effective H 2 O 2 generation and activation simultaneously. • The novel process is more effective for pollutants degradation than Pd-catalytic EF process. The Electro-Fenton (EF) process is one of the promising advanced oxidation processes (AOPs) for environmental remediation. The H 2 O 2 yield of EF process largely determines its performance on organic pollutants degradation. Conventional Pd-catalytic EF process generates H 2 O 2 via the combination reaction of anodic O 2 and cathodic H 2 . However, the relatively expensive catalyst limits its application. Herein, a hybrid Pd/activated carbon (Pd/AC)-stainless steel mesh (SS) cathode (PACSS) was proposed, which enables more efficient H 2 O 2 generation. It utilizes AC, the support of Pd catalyst, as part of cathode for H 2 O 2 generation via 2-electron anodic O 2 reduction, and SS serve as a current distributor. Moreover, H 2 O 2 could be catalytically decomposed upon AC to generate highly reactive OH, which avoids the use of Fe 2+ . Compared with conventional Pd catalyst, H 2 O 2 concentration obtained by PACSS cathode is 248.2% higher, the O 2 utilization efficiency was also increased from 3.2% to 10.8%. Within 50 min, 26.3%, 72.5%, and 94.0% H 2 O 2 was decomposed by Pd, AC, and Pd/AC. Fluorescence detection results implied that Pd/AC is effective upon H 2 O 2 activation for OH generation. Finally, iron-free EF process enabled by PACSS cathode was examined to be effective for reactive blue 19 (RB19) degradation. After continuous running for 10 cycles (500 min), the PACSS cathode was still stable for H 2 O 2 generation, H 2 O 2 activation, and RB19 degradation, showing its potential application for organic pollutants degradation without increase in the running cost.

Celluloses as Green Support of Palladium Nanoparticles for Application in Heterogeneous Catalysis: A Brief Review

Palladium (Pd) is considered as powerful catalyst in many organic syntheses of industrial importance, employed in areas like medicine, pharmacology, cosmetics, pesticides and degradation of organic pollutants. In heterogeneous catalysis, stabilization of Pd nanoparticles (NPs) is foremost to prevent aggregation for getting high catalytic efficiency. Celluloses, being green support, have been widely used in different forms such as bulk, modified or nanocelluloses for stabilizing Pd NPs. The unique properties like high mechanical strength, thermal stability, high functionality, insolubility in water and in most organic solvents and good anchoring ability with metal NPs had made them good support for Pd NPs. However, special attention is needed on further improving the binding efficiency of Pd NPs with cellulose without affecting the catalytic property for achieving long term recycle stability. This review will focus on the merits and demerits of the existing cellulose supported Pd catalysts and propose solutions to overcome the limitations.

Effect of Pd Precursor Salts on the Chemical State, Particle Size, and Performance of Activated Carbon-Supported Pd Catalysts for the Selective Hydrogenation of Palm Biodiesel.

To improve the oxidative stability of biodiesel fuel (BDF), the polyunsaturated fatty acid methyl esters (poly-FAME) presented in commercial palm oil-derived biodiesel fuel (palm-BDF) were selectively hydrogenated to monounsaturated fatty acid methyl esters (mono-FAME) under a mild condition (80 °C, 0.5 MPa) using activated carbon (AC)-supported Pd catalysts with a Pd loading of 1 wt.%. The partially hydrotreated palm-BDF (denoted as H-FAME) which has low poly-FAME components is a new type of BDF with enhanced quality for use in high blends. In this study, we reported that the chemical states and particle sizes of Pd in the prepared Pd/AC catalysts were significantly influenced by the Pd precursors, Pd(NO3)2 and Pd(NH3)4Cl2, and thus varied their hydrogenation activity and product selectivity. The 1%Pd/AC (nit) catalyst, prepared using Pd(NO3)2, presented high performance for selective hydrogenation of poly-FAME into mono-FAME with high oxidation stability, owning to its large Pd particles (8.4 nm). Conversely, the 1%Pd/AC (amc) catalyst, prepared using Pd(NH3)4Cl2, contained small Pd particles (2.7 nm) with a little Cl residues, which could be completely removed by washing with an aqueous solution of 0.1 M NH4OH. The small Pd particles gave increased selectivity toward unwanted-FAME components, particularly the saturated fatty acid methyl esters during the hydrogenation of poly-FAME. This selectivity is unprofitable for improving the biodiesel quality.

The Selective Oxidation of Cyclohexane via In-situ H2O2 Production Over Supported Pd-based Catalysts

The oxidation of cyclohexane via the in-situ production of H2O2 from molecular H2 and O2 offers an attractive route to the current industrial means of producing cyclohexanone and cyclohexanol (KA oil), key materials in the production of Nylon. The in-situ route has the potential to overcome the significant economic and environmental concerns associated with the use of commercial H2O2, while also allowing for the use of far lower reaction temperatures than those typical of the purely aerobic route to KA oil. Herein we demonstrate the efficacy of a series of bi-functional Pd-based catalysts, which offer appreciable concentrations of KA oil, under conditions where limited activity is observed using O2 alone. In particular the introduction of V into a supported Pd catalyst is seen to improve KA oil concentration by an order of magnitude, compared to the Pd-only analogue. In particular we ascribe this improvement in catalytic performance to the development of Pd domains of mixed oxidation state upon V incorporation as evidenced through X-ray photoelectron spectroscopy.Graphic

Sustainable direct H2O2 synthesis over Pd catalyst supported on mesoporous carbon: The effect of surface nitrogen functionality

We employed oxygen- and nitrogen-functionalized mesoporous carbons (OMC and N-OMC) as supports for Pd nanoparticles pre-formed via a modified colloidal method. In the direct synthesis of hydrogen peroxide (H2O2) from H2 and O2, the prepared Pd/OMC catalyst outperformed a commercial Pd catalyst supported on activated carbon (Pd/AC) and a Pd catalyst on oxygen-functionalized carbon nanotubes (Pd/OCNT) in terms of H2O2 productivity, emphasizing the advantage of mesoporous carbon support. An even higher H2O2 productivity was obtained over Pd catalyst supported on N-OMC with 2.72 at.% nitrogen on the surface. However, a further increase of surface nitrogen content to 13.26 at.%, as the case of mesoporous carbon directly grown using N-containing carbon precursor (NMC), led to increased activity (in terms of H2 consumption) but poor H2O2 productivity. X-ray photoelectron spectroscopy analyses of the Pd/MC catalysts suggest that a suitable amount of N groups (ca. 2.72 at.%) on the MC surface led to a high fraction of Pd2+ in the Pd/MC catalyst, which is believed to be important for achieving high selectivity in direct H2O2 synthesis. These results highlight that tuning the surface properties of carbon supports is a versatile approach to fabricate highly selective supported Pd catalysts for the sustainable direct synthesis of H2O2 from H2 and O2.

The effects of dopant on catalytic activity of Pd/mesoporous alumina for toluene oxidation

A series of mesoporous alumina (MA) doped with acidic (Ti, W) or alkaline earth (Ba, Mg) elements were prepared. They were used as the supports for Pd catalysts. These catalysts were characterized by N2 sorption, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, infrared spectroscopy of CO adsorption and temperature-programmed reduction. Complete oxidation of toluene on these catalysts was tested in a fixed-bed micro-reactor. The results of in situ IR of CO adsorption indicated that the doping of basic element was beneficial for the dispersion of PdO particles, while the doping of acid element suppressed the dispersion of PdO particles. The binding energy of Pd in Pd/Ba-MA shifted to high energy, indicating that the interaction between PdO and support was enhanced. The results of H2-TPR showed that the reducibility of PdO doped with alkaline element was stronger than those of catalysts doped with acidic element. The doping of basic elements promoted the dispersion of PdO particles, changed the electronic state of Pd and enhanced the reducibility of PdO, which led to its high activity. The catalysts doped with the basic elements had higher activities than those doped with acidic elements, among which the Pd/Ba-MA catalyst had the highest activity among all catalysts.

Nitrogen doped carbon for Pd-catalyzed hydropurification of crude terephthalic acid: roles of nitrogen species.

The purification of crude terephthalic acid was performed by the hydrogenation of 4-carboxybenzaldehyde (4-CBA) over activated carbon (AC) supported Pd catalysts in industry. However, traditional Pd/AC catalysts usually suffer from low hydrogenation activity and poor thermal stability. Herein, nitrogen was incorporated into AC via a simple hydrothermal treatment of AC with urea as the nitrogen resource. The N doped AC contained pyridinic N, pyrrolic N, graphitic N and oxidized N. Wide characterizations revealed that N doping not only effectively improved the dispersion of Pd NPs but also increased the proportion of Pd0. In addition, N doping also enhanced the dissociative adsorption capacity of molecular hydrogen. More importantly, the resistance to sintering of Pd NPs was efficiently suppressed after N doping. As a result, N doped AC supported Pd showed both higher activity and better thermal stability than the N-free one.

Oxygen vacancy and nitrogen doping collaboratively boost performance and stability of TiO2-supported Pd catalysts for CO2 photoreduction: a DFT study.

The regulation of interfacial charge transfer, optimization of active sites, and maintenance of stability are effective strategies for improving catalytic performance. The effect of the oxygen vacancy (VO) and nitrogen doping on these parameters for CO2 photoreduction on Pd10/TiO2(101) was studied using density functional theory calculations. The results demonstrate that introduction of the VO could trigger reversed electron transfer, making the VO and Pd atoms the active center for CO2 reduction. However, the VO is repaired by the dissociated O atom. The combined effect of the VO and N is related to the position of N. Although the substitutional N (NS) can delocalize electrons at the VO, it cannot improve the activity and stability. The interstitial N (Ni) located below the VO forms Ni-Ti bonds with two Ti atoms adjacent to the VO. This can delocalize the electrons near the VO, and the five-fold-coordinated titanium (Ti5C) replaces the VO as the active center, thus enhancing the reactivity and protecting the VO. Further research indicates that the co-modification of the VO and Ni improves photoexcited electron transfer and distribution, which would in turn promote CO2 reduction. The results of this study propose that surface defect engineering holds great promise for boosting CO2 photoreduction by integrating functions of electron density modulation and catalysis.

Development of Pd-supported Catalysts for the Conversion of Palm Oil to Biohydrogenated Diesel in a Microscale-based Reactor

In this research, the preparation of Pd-supported catalysts in microreactor was investigated for the production of renewable biohydrogenated diesel (BHD). Pd/Al2O3 and Pd/TiO2 catalysts were prepared by two different coating methods, slurry suspension (SUS), and sol-gel method (SG). Catalysts were coated on microreactor walls and tested for the deoxygenation of palm oil to BHD at 325 ºC, 3.4 MPa, H2/feed molar ratio of 96. The coated catalysts were characterized by several techniques, including 3D-optical profiler, SEM-EDX, XRD, BET, and adhesion test. The experimental results show that SUS method provided a homogeneous catalyst layer, while the SG method gave a non-homogeneous cracked coating. In terms of catalytic activity, Pd/TiO2 (SG) exhibited the highest space-time yield (STY) of BHD (g BHD g–1 catalyst h–1), which could be due to its unique characteristics of pure anatase phase and strong metal-support interaction for hydrogen spillover mechanism.

Palladium supported on structurally stable phenanthroline-based polymer nanotubes as a high-performance catalyst for the aqueous Suzuki–Miyaura coupling reaction

One-dimensional Pd-supported catalyst exhibits excellent catalytic activity since its TOF value is 3077 h−1for the Suzuki–Miyaura coupling reaction of bromobenzene and phenylboronic acid under ambient conditions.

Catalytic Consequences of Supported Pd Catalysts on Dehydrogenative H2 Evolution from 2-[(n-Methylcyclohexyl)methyl]piperidine as the Liquid Organic Hydrogen Carrier

Herein, nanoporous Al2O3, CeO2, TiO2, ZrO2, and SnO2 were used as the supports for Pd nanoparticles, and effects of surface characteristics on catalytic performances for dehydrogenation of 2-[(n-methylcyclohexyl)methyl]piperidine (H12-MBP) as the H2-rich liquid organic hydrogen carrier were investigated. The H2 yield, dehydrogenation rate, product selectivity, and recyclability of the supported Pd catalysts depended on the metal oxide support and Pd loading. The H2 yield and reaction rate of the Al2O3 supporting 5 wt % Pd with a mean size of 5.76 nm were the highest (75.8%) and the fastest (k1 = 0.076 min–1), respectively, of all the catalysts. CeO2 exhibited the highest reducibility and the best supporting ability for Pd nanoparticles, which thus dispersed Pd with the smallest mean size of 3.45 nm. Although this catalyst exhibited a lower H2 yield (67.1%) and a slower reaction rate (k1 = 0.030 min–1) than Al2O3, it showed the best recyclability without a significant loss of activity during four consecutive runs, which could be attributed to the strong metal–support interaction of Pd to the surface of CeO2. The H2 yield and the dehydrogenation rate were systematically correlated with the surface characteristics of the metal oxides, such as acidity, adsorption affinity (adsorption energy), and charge transfer value of H12-MBP, which were determined via combined experimental and theoretical studies.

Investigation of hydrazine electrooxidation performance of carbon nanotube supported Pd monometallic direct hydrazine fuel cell anode catalysts

In this study, carbon nanotube (CNT) supported Pd catalysts at varying Pd molar ratios are prepared via NaBH4 reduction method. Catalysts prepared for hydrazine electrooxidation are characterized via N2 adsorption-desorption measurements (BET), X-ray photoelectron spectroscopy (XPS), and transmission electron microscope (TEM). Electrochemical measurements are performed using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques by CHI660E potentiostat in a three-electrode system. According to the characterization results, Pd/CNT catalysts are successfully synthesized. For 5% Pd/CNT catalyst, the average particle size and the surface area determined as 5.17 nm and 773.10 m2 g-1 via TEM and BET, respectively. Between the Pd containing (0.1-20 wt %) CNT supported catalysts prepared, 5% Pd / CNT catalyst shows the best current density as 6.81 mA cm-2 (1122.63 mA mg-1 Pd). Furthermore, 5% Pd/CNT catalyst shows littlest charge transfer resistance (Rct) compared to Pd/CNT catalysts.

Hydrogen production from additive-free formic acid over highly active metal organic frameworks-supported palladium-based catalysts

The metal organic frameworks (MOFs) supported Pd catalysts for H2 generation from formic acid (FA) were synthesized in this work, via a facile excessive impregnation-low temperature reduction approach. Among the synthetic catalysts, 10% Pd/MOF-Cr (18) displayed a remarkable performance for catalyzing FA dehydrogenation in additive-free aqueous solution, and the corresponding TOFmid achieved 537.8 h−1 at 323 K. Furthermore, the bimetallic Ni–Pd alloy catalysts were prepared by the introduction of Ni in the subsequent work. Fortunately, 10% Ni0.4Pd0.6/MOF-Cr was found to be a highly active and fairly durable catalyst, exhibiting a TOFmid as high as 737.9 h−1 at 323 K with almost 100% XFA (final) and SH2, and remained 94% of its original activity in the third cyclic catalysis. Meanwhile, Ni was discovered to be indispensable in increasing the electron density of Pd, downsizing the immobilized metal particles and inhibiting the agglomeration of the loaded nanoparticles.

A first-principles study of reaction mechanism over carbon decorated oxygen-deficient TiO2 supported Pd catalyst in direct synthesis of H2O2

The choice of support is one of the most significant components in the direct synthesis of H 2 O 2 . Aiming to improvement of activity and selectivity of H 2 O 2 on Pd/TiO 2 surface, we systematically investigated the important elementary steps on Pd/TiO 2 -Vo@C, Pd/TiO 2 -Vo, Pd/TiO 2 -2Vo, Pd/TiO 2 , and Pd/C using the first-principles calculations. The Bader charge analysis and charge density difference of O 2 adsorption elucidate the relationship between the electronic distribution and chemisorption energy. The effective barrier analysis further enables to quantitatively estimate the reactivity of H 2 O 2 and H 2 O. We demonstrate unambiguously that the selectivity of H 2 O formation is boosted as the oxygen vacancy concentration raised. Moreover, the introduction of C into a TiO 2 with appropriate oxygen vacancies can slightly reduce the effective barrier for H 2 O 2 formation and increase the effective barrier for H 2 O formation leading to a higher activity and selectivity of H 2 O 2 formation. Our finding suggests that carbon-doped oxygen vacancy TiO 2 supported Pd is potential alternative catalyst compared with the Pd/TiO 2 .

Vicinal hydroxyl group-inspired selective oxidation of glycerol to glyceric acid on hydroxyapatite supported Pd catalyst

Selective oxidation of glycerol provides a feasible route towards the sustainable synthesis of high value-added chemicals. Herein, the hydroxyapatite (HAP) supported palladium (Pd) species were fabricated by impregnation and subsequent calcination. The as-obtained heterogeneous Pd catalyst afforded not only excellent selectivity to glyceric acid (GLA) up to 90% with 59% conversion of glycerol but also good recyclability by using molecular oxygen as an oxidant under mild conditions. The characterization of catalysts indicated that both the surface basicity and Pd sites on the catalyst played a crucial role in promoting glycerol oxidation. Notably, it demonstrated that the presence of the vicinal hydroxyl group of glycerol molecule can assist the oxidation reaction via forming a coordination between the vicinal hydroxyl group and Ca2+ sites on HAP-derived catalysts. In this catalytic process, the secondary hydroxyl of glycerol kept untouched and the primary hydroxyl of glycerol was converted into carboxyl group, while the Pd species acted as active centers for cooperatively promoting the subsequent oxidation to generate GLA. Additionally, this catalytic system can be extended widely for the oxidative conversion of other vicinal diols into the corresponding α-hydroxycarboxylic acids selectively. Isotope labeling experiment using H218O confirmed that H2O not only acted as solvent but also was involved in the catalytic cycles. On the basis of the results, a possible reaction mechanism has been proposed. The HAP-supported Pd catalytic system has been shown to serve as an effective approach for the upgrading of bio-derived vicinal diols to high value-added chemicals.

The rule of N in N-doped graphene supported Pd catalyst

Using first-principles calculations, the rule of N in N-doped graphene supported Pd catalyst was investigated. Our results show that the doped N enhanced the adsorption and charge of Pd, which can lead to higher catalytic activity. Meanwhile, the doped N can also enhance the adsorption of H and make it more difficult to migrate on graphene. But the doped N is conductive to overflow of H from the Pd to graphene, the energy barrier is reduced from 1.01 eV to 0.85 eV. Therefore, it is speculated that one migration path of H on the N-doped graphene through the Pd atom.

Unexpected electocatalytic activity of a micron-sized carbon sphere-graphene (MS-GR) supported palladium composite catalyst for ethanol oxidation reaction (EOR)

For the first time, a hybrid carbon material consisting of micron-sized carbon spheres and graphene (denoted as MS-GR) was prepared via a hydrothermal method. In this work, micron-sized carbon spheres were prepared using glucose and 1-butyl-3-methylimidazolium tetrafluoroborate as the starting materials through a hydrothermal method, and graphene was employed as purchased. One-pot and two-step hydrothermal methods were respectively employed to prepare MS-GR, and in each preparation method, three different amounts of graphene were added in the preparation system while maintaining the added amounts of other reagents identical for each prepared catalyst. As a result, six kinds of hybrid carbon materials were fabricated in this work. Next, MS-GR supported palladium composite catalysts were fabricated through a hydrothermal method using PdO·H2O as the palladium source. Metallic Pd particles, metallic Pd particles along with PdO were indicated by XRD patterns to be the main substances of the one-pot and two-step hydrothermally prepared MS-GR supported catalysts, respectively. As presented by the SEM images, micron-sized carbon spheres and individual graphene sheets as well as the small particles were exhibited clearly in all prepared catalysts, suggesting that all the resultant catalysts were a composite material. Most importantly, as indicated by the CV and CA curves, all synthesized catalysts showed obvious electrocatalytic activities for EOR. In particular, the peak current density of peak f for EOR in the CV curves on catalyst t-4 was as high as 29.1 mA cm-2, significantly larger than the previously reported values. And the current density of EOR measured by CA test on catalyst t-4 was retained as high as 2.83 mA cm-2 after 600 s, showing an excellent electrocatalytic durability. In this work, a carbon material constructed by micron-sized carbon spheres and graphene as well as a novel MS-GR supported Pd catalyst was developed for the first time, which was very helpful to the final commercialization of a Pd-based EOR electrocatalyst due to the greatly reduced the preparation cost and the facile preparation procedure.

Conversion of syngas to methanol and DME on highly selective Pd/ZnAl2O4 catalyst

Supported Pd catalysts with varied Pd loadings (x = 0.5 wt%, 2.0 wt%, 5.0 wt%, 7.5 wt%, 15.0 wt%) were prepared by the incipient wetness impregnation method using a ZnAl2O4 spinel support. We found that ZnAl2O4 supported Pd catalysts with low Pd loadings (e.g., 0.5 wt%) are very selective in syngas conversion to methanol and dimethyl-ether (DME). XRD and TEM characterization shows that, after reduction at 350 °C, PdZnβ phase with Pd:Zn molar ratio of 1:1 is favored to form predominantly on the spinel support at relatively low Pd loadings, i.e. less than 5.0 wt%, while Pd-rich PdZnα alloy phase exists at Pd loadings above 5.0 wt%. A higher reduction temperature such as 500 °C can facilitate the transformation from PdZnα to PdZnβ phase in those catalysts with high Pd loading. We further found that catalysts with predominant PdZnβ phase are selective in the methanol and DME production from syngas, while the presence of PdZnα phase leads to the notable formation of alkanes byproducts, resulting in reduced methanol and DME selectivity. DME formation from dehydration of methanol depends on the acidity of catalysts, which was found to increase with Pd loading, probably due to the formation of isolated Al2O3 as a result of Zn migrating from ZnAl2O4 spinel phase to form the PdZn phases with Pd.