Topics in Catalysis

Here we describe studies of the fine structure of zeolites by TEM started at Cambridge in 1982. These include investigations of coincidence boundaries in LTL, the surface structures of FAU and EMT, the surface structures of LTL and supported metal clusters and the structural relation between MFI and MEL. These, combined with present studies of mesoporous crystals and nanostructured materials demonstrate the strength of electron microscopy in this field of material science.

Alumina supported Cu–Mn mixed oxide with Cu/Mn molar ratio 2:1 was used as a support of gold and silver catalysts for oxidation of CO, methanol and dimethylether. Different techniques (XRD, HRTEM, XPS, FTIR, EPR, and TPR) were used to investigate structure–reactivity relationship. A strong effect of the nature of the promoters on the catalytic behaviour was observed. Superior catalytic activity in oxidation of CO was measured after addition of Au, while modification by Ag affected very slightly the CO oxidation activity of Cu/Mn 2:1 sample. Both Au and Ag have beneficial effect on CH3OH oxidation activity of Cu–Mn mixed oxides. The combination of the good redox properties of Cu–Mn mixed oxides and gold nanoparticles has proved to be an advantageous approach for developing new catalytic formulations with high effectiveness to eliminate different type pollutants in waste gases from formaldehyde production. The use of high surface area support is beneficial for the stabilization of gold particles in a highly dispersed state and contributes for economic viability in case of practical applications, because of the composition of this catalytic system, that is mostly alumina (80 %).

Efficient utilization of CO2 to produce clean liquid fuels and various petrochemicals has attracted significant attention during the past decades. This review mainly focuses on our efforts and main achievements during the development of a CO2-utilizing Gas-to-Methanol (CGTM) process, which is composed of CO2/steam-mixed reforming and methanol synthesis via CO2 and CO hydrogenation. Experimental apparatus at different scales, ranging from lab to demonstration, have been established to pursue an efficient CGTM process with enhanced energy efficiency and reduced CO2 emissions. The proposed CGTM process employs a proprietary coke-resistant Ni-based catalyst in the reforming section, which is very stable under a 1000-h accelerated stability test. Based on the results of the process simulation and optimization obtained by using Aspen Plus, a CGTM demonstration plant with a methanol-production capacity of 10 t/day is designed and constructed, which comprises a reforming section (co-feeding CO2 into the reformer), a methanol synthesis section, and a recycling section. During the continuous operation for 1000 h, the CGTM demonstration plant exhibited a satisfactory performance, which is in good agreement with the design values. The overall thermal efficiency is shown to be superior to that of the conventional Gas-to-Methanol (GTM) processes, and the CGTM process is economically feasible given that the NG price, methanol price, and the plant scale are located in the following range of 1–5 $/MMBTU, 350–500 $/Mt, and 2500–5000 TPD, respectively. Furthermore, the proposed CGTM process would be even more competitive in the case of a higher carbon tax.

Nano Fe-BTC/graphene oxide (GO) composites were successfully synthesized by hydrothermal treatment with a microwave-assisted method. Samples were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), N2 adsorption–desorption, Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), and Ultraviolet–visible diffuse reflection spectroscopy (UV–Vis DRS). SEM image of Fe-BTC/GO-30 showed the particle size of 30–50 nm on the GO surface. From the UV–Vis diffuse reflectance spectra, it revealed that nano Fe-BTC/GO composite absorbed the wavelengths in the visible light region with a low bandgap energy of 2.2–2.45 eV. Fe-BTC/GO nanocomposites were tested for the photocatalytic degradation of reactive yellow 145 (RY-145) in aqueous solution. Fe-BTC/GO composites exhibited high photocatalytic activity. Thus, at pH of 3 and high initial concentration of 100 mg RY-145/L, removal efficiency reached the value of 98.18% after 60 min. of reaction. In comparison with Fe-BTC/GO synthesized by the solvothermal method, nano Fe-BTC/GO showed much higher RY-145 removal efficiency. Moreover, this Fe-BTC/GO-30 showed high catalytic activity stability and could be reused, opening the high potential application of this promising photo-Fenton catalyst in photocatalytic degradation of organic pollutants from aqueous solution.

The study of magnetic perovskite oxides has led to novel and very active compounds for O2 generation and other energy applications. Focusing on three different case studies, we summarise the bulk electronic and magnetic properties that initially serve to classify active perovskite catalysts for the oxygen evolution reaction (OER). Ab-initio calculations centred on the orbital physics of the electrons in the d-shell provide a unique insight into the complex interplay between spin dependent interactions versus selectivity and OER reactivity that occurs in these transition-metal oxides. We analyse how the spin, orbital and lattice degrees of freedom establish rational design principles for OER. We observe that itinerant magnetism serves as an indicator for highly active oxygen electro-catalysts. Optimum active sites individually have a net magnetic moment, giving rise to exchange interactions which are collectively ferromagnetic, indicative of spin dependent transport. In particular, optimum active sites for OER need to possess sufficient empty orthogonal orbitals, oriented towards the ligands, to preserve an incoming spin aligned electron flow. Calculations from first principles open up the possibility of anticipating materials with improved electro-catalytic properties, based on orbital engineering.

We present density functional theory calculations on the direct synthesis of H2O2 from H2 and O2 over an Au12 corner model of a gold nanoparticle. We first show a simple route for the direct formation of H2O2 over a gold nanocatalyst, by studying the energetics of 20 possible elementary reactions involved in the oxidation of H2 by O2. The unwanted side reaction to H2O is also considered. Next we evaluate the degree of catalyst control and address the factors controlling the activity and the selectivity. By combining well-known energy scaling relations with microkinetic modeling, we show that the rate of H2O2 and H2O formation can be determined from a single descriptor, namely, the binding energy of oxygen (EO). Our model predicts the search direction starting from an Au12 nanocluster for an optimal catalyst in terms of activity and selectivity for direct H2O2 synthesis. Taking also stability considerations into account, we find that binary Au–Pd and Au–Ag alloys are most suited for this reaction.

Việc kích hoạt CO2 bằng cation Gadolinium (Gd+) theo quá trình tỏa nhiệt và không có rào cản để tạo ra GdO+ và CO được nghiên cứu một cách chi tiết bằng cách sử dụng phổ khối ion hướng dẫn và lý thuyết (GIBMS). Các tiết diện ngang ion sản phẩm phụ thuộc vào năng lượng động học từ các thí nghiệm phân tích phân li do va chạm (CID) của GdCO2+ được đo để xác định năng lượng của các trung gian OGd+(CO) và Gd+(OCO). Việc mô phỏng các tiết diện này cho ra năng lượng phân rã liên kết (BDEs) cho OGd+–CO và Gd+–OCO lần lượt là 0.57 ± 0.05 và 0.38 ± 0.05 eV. BDE của OGd+–CO tương tự như giá trị đã được đo trước đó cho Gd+–CO, điều này có thể được quy cho sự tương tác tĩnh điện tương đương với CO trong cả hai phức hợp. Phức hợp Gd+(OCO) được xác định từ các phép tính tương ứng với trạng thái kích thích điện tử. Nhiệt hóa học ở đây và BDE GdO+ mới được đo cho phép suy ra bề mặt năng lượng tiềm năng (PES) của phản ứng Gd+ với CO2 từ thí nghiệm một cách chi tiết. Các phép tính lý thuyết được thực hiện để so sánh với nhiệt hóa học thực nghiệm và để tìm hiểu về các trạng thái điện tử của các trung gian GdCO2+, các trạng thái chuyển tiếp và cơ chế phản ứng. Mặc dù phản ứng giữa Gd+ trạng thái cơ bản (10D) và các chất phản ứng CO2 (1Σg+) để tạo ra sản phẩm GdO+ trạng thái cơ bản (8Σ−) và CO (1Σ+) chính thức bị cấm quay, các phép tính cho thấy có các bề mặt tám nguyên tử và mười nguyên tử có khoảng cách năng lượng nhỏ trong kênh vào, giúp chúng có thể trộn lẫn dễ dàng. Do đó, phản ứng có thể tiến triển hiệu quả theo bề mặt tám nguyên tử năng lượng thấp nhất để sản xuất các sản phẩm trạng thái cơ bản, đồng nhất với các quan sát thực nghiệm về một quá trình hiệu quả, không có rào cản. Ở năng lượng va chạm cao, tiết diện ngang GdO+ đo được từ phản ứng của Gd+ với CO2 cho thấy một đặc điểm riêng biệt, được quy cho sự hình thành các sản phẩm GdO+ kích thích điện tử trên một bề mặt PES mười nguyên tử trong quá trình diabatic và cho phép quay. Việc mô phỏng đặc điểm năng lượng cao này cho ra năng lượng kích thích là 3.25 ± 0.16 eV so với trạng thái GdO+ (8Σ−) cơ bản, phù hợp với các năng lượng kích thích đã tính toán cho các trạng thái điện tử GdO+ (10Π, 10Σ−). Tính phản ứng của Gd+ với CO2 được so sánh với các cation kim loại chuyển tiếp nhóm 3 và các cation lanthanide khác và các xu hướng chu kỳ được thảo luận.

In the context of CO2 valorisation, the reverse water–gas shift reaction (RWGS) is gathering momentum since it represents a direct route for CO2 reduction to CO. The endothermic nature of the reaction posses a challenge when it comes to process energy demand making necessary the design of effective low-temperature RWGS catalysts. Herein, multicomponent Cs-promoted Cu, Ni and Pt catalysts supported on TiO2 have been studied in the low-temperature RWGS. Cs resulted an efficient promoter affecting the redox properties of the different catalysts and favouring a strong metal-support interaction effect thus modulating the catalytic behaviour of the different systems. Positive impact of Cs is shown over the different catalysts and overall, it greatly benefits CO selectivity. For instance, Cs incorporation over Ni/TiO2 catalysts increased CO selectivity from 0 to almost 50%. Pt-based catalysts present the best activity/selectivity balance although CuCs/TiO2 catalyst present comparable catalytic activity to Pt-studied systems reaching commendable activity and CO selectivity levels, being an economically appealing alternative for this process.