Vanadia-Based Catalysts for the Sulfur Dioxide Oxidation StudiedIn Situby Transmission Electron Microscopy and Raman Spectroscopy

Abstract

The industrial production of sulfuric acid involves the oxidation of sulfur dioxide, which is catalyzed by a silica-supported phase consisting of V 2 O 5 species dissolved in a pyrosulfate melt with Na, K, and Cs added as promoters. As the molten phase is only present during the catalytic reaction and solidifies at room temperature, in situ studies are necessary to address the working state of the SO 2 oxidation catalyst. Here we combine transmission electron microscopy (TEM) and Raman spectroscopy to study in situ a vanadia-based SO 2 oxidation catalyst upon activation and reaction in an SO 2 / O 2 gas mixture. The observations reveal that the vanadia phase dynamically redistributes on the support upon heating in an SO 2 /O 2 mixture. Surprisingly, the vanadia phase can disperse into partially crystalline islands on convex surfaces of the silica support and into a molten state on concave areas of the support. The presence of Cs was found to lower the temperature for the pyrosulfate formation and stabilize vanadium in the active V V state by forming linked structures at low temperature. Combining these in situ studies with activity measurements leads to the proposal that the linked structures stabilize the catalyst in the active state.

Quantitative Structure–Activity Relationship of Nanowire Adsorption to SO2 Revealed by In Situ TEM Technique

“…Compared with conventional TEM characterization, in situ TEM can directly record the morphological evolution of a material under the desired atmosphere. The video recorded in real time provides valuable experimental data for quantitatively investigating the kinetics of solid–gas reactions. − To date, some reducing/oxidizing gases, including H 2 and O 2 , have been successfully introduced into in situ TEM for solid–gas reaction investigation. − However, in situ TEM observation for solid–gas reaction involving the corrosive SO 2 gas is difficultly to be conducted, thereby is seldom reported . It is worth noting that SO 2 -involved solid–gas interactions play an essential role in a wide range of applications, such as environmental protection, modern industry, and human health, and deserve to be investigated urgently. − …”

“…involving the corrosive SO 2 gas is difficultly to be conducted, thereby is seldom reported. 43 It is worth noting that SO 2involved solid−gas interactions play an essential role in a wide range of applications, such as environmental protection, modern industry, and human health, and deserve to be investigated urgently. 3−7 Herein, gas-cell in situ TEM is applied to observe the morphological evolution of ZnO nanowires in real time under SO 2 atmosphere (Figure 1).…”

A Novel Raman Setup Based on Magnetic-Driven Rotation of Sample

“…toward in situ and/or operando conditions. Indeed, few pioneering examples are encountered in the literature [15,13,24,12,16,14,27,28].…”

“…This cell exploits the catalytic bed fluidization too, but it is based on a fully fluid-dynamic concept: the powder is fluidized by backflow pulses with regular frequency, produced via dedicated device. The versatility of this tool has been demonstrated by application involving several heterogeneous catalysts [12,27,28]. Despite its excellent capability to preserve the sample from laserdegradation, fluidization is also a possible source of drawbacks: i) unavoidably the sample is partially lost during the experiment, limiting the time framework available to perform it; ii) the continuous friction among the particles leads to their progressive morphological modification, so that occasionally the fluidization conditions (strongly connected to the particles shape and size) are no longer achievable iii) in presence of condensable vapors, the wetting of the catalyst can prevent the fluidization to occur; and iv) since a gas flow is required to fluidize the powder, the reactor-cell is not suitable for working in batch (i.e.…”

Surface Topotactic Growth of Edge-Terminated MoS2 Catalysts

“…While technology has become available for high spatial and temporal resolution TEM of nanomaterials under reactive gas environments [6], sulfur-containing gases are challenging by being highly corrosive to the microscope equipment. To overcome this challenge, we have upgraded a differentially pumped TEM instrument to dedicated in situ studies of chemical reactions involving sulfur [7,8]. This instrument was used to acquire time-resolved TEM image series of MoO2 nanocrystals in situ during exposure to H2S/H2 gas mixtures at elevated temperatures [9].…”