Performance Of Bimetallic Catalysts Research Articles

Hydrogen production from steam reforming of acetic acid over Pt–Ni bimetallic catalysts supported on ZrO2

Acetic acid, a model compound of bio-oil, was chosen to investigate the H2 production from steam reforming reaction using Pt and Ni catalysts supported on ZrO2. Ni crystallite sizes decreased with addition of Pt (from 23 to 15 nm), increasing the metallic dispersion (from 4.4 to 6.5%). A spillover effect was identified in bimetallic catalysts and caused a significant decrease of Ni reduction temperature. Although the Ni crystallite size in 15Ni/ZrO2 is larger, it showed 100% of conversion and the highest H2 yield (about 30%) during 30 h of reaction at 500 °C. In contrast to what was expect, the performance of bimetallic catalysts was not so good when compared to the monometallic Ni catalyst. 5Pt15Ni/ZrO2 and 1Pt15Ni/ZrO2 showed about 20% of H2 yield at the end of reaction. 1Pt/ZrO2 presented the worst catalytic performance; it produced more acetone, which can be correlated to its higher acidity, and deactivated very fast, with the highest coke formation rate. Coke was predominantly amorphous for all catalysts.

Hydrogen production from steam reforming of ethanol over Ni-Co bimetallic catalysts and MCM-41 as support

Abstract Catalytic Steam reforming of ethanol (SRE) is a promising method for the generation of H2 as a clean carrier of energy. In this study, the impregnation method was deployed to prepare mono and bimetallic catalyst Nix-Co(10-x) (x = 10, 9, 8, 5 and 0) loaded on MCM-41 nanoparticles as the catalyst for the SRE reaction. The characteristics of the synthesized catalysis were identified using BET, XRD, EDS, FESM, and TGA/DTA analysis in a fixed bed micro-reactor, the gases were constantly monitored by using gas chromatography (GC). The purpose of this project is to optimize the reaction conditions using synthesized catalysts and to find the best catalyst. The effects of reaction temperature (420–500 °C) and molar ratios of steam to ethanol (S/E = 2, 3 and 5) were studied in detail over this catalyst. According to the results, the performance of bimetallic catalysts is very high compared to mono metal catalyst. Between mono metal catalysts Nickel was active rather than Cobalt. Ni9 Co1/MCM-41 catalysts displayed the best catalytic performance, so that the conversion of ethanol was 90% and highest hydrogen yield of 80% were achieved at the temperature of 490°C, S/E = 5 and under the atmospheric pressure.

Effect of Rh Addition to Ni/MgO-Al2O3 Catalysts for Dry Reforming of Methane

Objective: This study has analyzed the performance of Ni and Ni-Rh catalysts based on MgO/g-Al2 O3 in the process of dry reforming of methane (DRM). Methods/Statistical Analysis: The samples were prepared using the incipient wetness impregnation method and were characterized by N2 adsorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), diffuse reflectance spectroscopy (DRS), surface acidity, X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), and Raman spectroscopy. The catalysts were reduced with hydrogen and measured in the reaction of CH4 with CO2 at two CH4 /CO2 ratios. Findings: The 0.5% Rh addition to Ni/MgO-g-Al2 O3 improves the activity and the stability for this process. In the bimetallic catalysts, the reduction temperature of the active phase decreases due to the hydrogen spillover mechanism from the noble metal to the catalyst surface, which favors their catalytic activity. On the other hand, the interaction between Rh and the support would be the cause for the better performance of bimetallic catalysts. The Rh-Ni/MgO-g-Al2 O3 catalyst is the most active, indicating that the impregnation order affects the catalytic behavior. Improvements/Applications: This study gives promising results for this type of catalyst, also showing the effect of the catalyst preparation on the activity and its relationship with deactivation by coke. Keywords: Dry Reforming of Methane, Oxides, Rh-Ni Catalysts, Raman Spectroscopy and Scattering, Surface Properties

Understanding the Performance and Stability of Supported Ni-Co-Based Catalysts in Phenol HDO

Performances of bimetallic catalysts (Ni-Co) supported on different acidic carriers (HZSM-5, HBeta, HY, ZrO2) and corresponding monometallic Ni catalysts in aqueous phase hydrodeoxygenation of phenol were compared in batch and continuous flow modes. The results revealed that the support acidity plays an important role in deoxygenation as it mainly controls the oxygen-removing steps in the reaction network. At the same time, sufficient hydrothermal stability of a solid catalyst is essential. Batch experiments revealed 10Ni10Co/HZSM-5 to be the best-performing catalyst in terms of conversion and cyclohexane yield. Complementary continuous runs provided more insights into the relationship between catalyst structure, efficiency and stability. After 24 h on-stream, the catalyst still reveals 100% conversion and a slight loss (from 100% to 90%) in liquid hydrocarbon selectivity. The observed alloy of Co with Ni increased dispersion and stability of Ni-active sites, and combination with HZSM-5 resulted in a well-balanced ratio of metal and acid sites which promoted all necessary steps in preferred pathways. This was proved by studies of fresh and spent catalysts using various characterization techniques (N2 physisorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and infrared spectroscopy of adsorbed pyridine (pyr-IR)).

The study of bimetallic Ni–Co/cordierite catalyst for cracking of tar from biomass pyrolysis

In order to crack the tar from biomass pyrolysis, five cordierite-supported monolithic catalysts with different Ni/Co ratio were prepared by vacuum wetness impregnation. All catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), Brunauer–Emmett–Teller (BET), and scanning electron microscope (SEM). XRD and XPS characterization results show the inexistence of spinel structure such as NiAl2O4 and CoAl2O4. TPR characterization results suggest the possible formation of Ni–Co alloy. BET characterization results show that the effect of Ni/Co ratio on catalyst specific surface area is obvious. The catalytic test results show that the performance of bimetallic catalyst is better than that of monometallic catalyst. The Ni3Co1/cordierite catalyst exhibits the best catalytic performance among all bimetallic catalysts, its tar conversion and gas yield reach 96.4% and 1.21 Nm3/kg, respectively, at a weight hourly space velocity (WHSV) of 1.4 h−1.

Interplay between Layer-Resolved Chemical Composition and Electronic Structure in a Sn/Pt(110) Surface Alloy

Pt–Sn alloys play an important role as oxygen reduction reaction (ORR) catalysts in fuel cell technology both for their role in rationalizing the mechanism responsible for the better performances of bimetallic catalysts and for their practical applications. Here we present a complete experimental and theoretical study on the geometric and electronic structure of a (4×1) termination over a Pt3Sn near-surface ordered alloy obtained by depositing Sn on the Pt(110) and subsequent annealing. LEED and STM measurements combined with DFT simulations allow us to determine the atomistic structure of this phase, and to rationalize the peculiar dependence of its STM pattern on the applied bias and the compositional order in deep layers. Both photoemission experiments and density functional calculations indicate that in this phase the Sn–Pt alloying process determines important changes in the electronic properties, and in particular a relevant shift of the Pt 5d band centroid with respect to clean Pt.

Geometric Parameter Effects on Ensemble Contributions to Catalysis: H2O2 Formation from H2 and O2 on AuPd Alloys. A First Principles Study

Using first principles calculations, we examine how the ensemble effect on the performance of bimetallic catalysts is affected by the change of surface electronic structure associated with their geometric parameters. We look at H2O2 formation from H2 and O2 based on three different Pd monomer systems including AuPd adlayers with a Pd monomer each on Pd(111) [AuPdM/Pd(111)] and Au(111) [AuPdM/Au(111)] and a 55-atom cluster with Au41Pd shell and Pd13 core [Au41Pd@Pd13]. Our calculations show that H2O2 selectivity tends to be significantly deteriorated in the Au41Pd@Pd13 and AuPdM/Au(111) cases, as compared to the AuPdM/Pd(111) case. This is largely due to enhancement of the activity of corresponding surface Pd and its Au neighbors, while isolated Pd surface sites surrounded by less active Au are responsible for the H2O2 formation by suppressing O−O cleavage. This study highlights that ensemble contributions in multimetallic nanocatalysts can be a strong function of their geometric conditions, particularly l...