In Situ: Bridging the Gap Between Industry and the Laboratory

Introduction 

The term in situ appears frequently in academic literature across many fields. Although its exact meaning varies from discipline to discipline, it generally refers to observing or analyzing a subject or phenomenon in its original place or under conditions close to its actual operating environment. 

In other words, in situ seeks to preserve the context in which a phenomenon occurs. Rather than separating the subject from its surroundings or placing it in an overly artificial setting, it attempts to maintain the relevant environment as much as possible. 

At first glance, in situ may seem somewhat distant from reality because it is often associated with controlled laboratory conditions. In fact, however, it has a strongly practical character. Its purpose is to reflect the conditions under which a system actually functions. Of course, depending on how a specific system is designed, those conditions may be more idealized or more realistic. 

In this post, I first examine how the concept of in situ developed over time. I then look at how the term has been used across different fields and why it has become especially important in catalysis research. Finally, using my paper published in the Journal of Youth Impact, “Cooperative Integration of SCR and CESAR-1: Focused on Mechanism and Performance,” as a case study, I consider what aspects of the study could be improved from an in situ perspective and how this perspective could shape my future research. 

The Historical Development of In Situ 

In situ is a Latin expression that has become established in modern English with the meaning “in its original place” or “in position.” Dictionary sources suggest that the term was in use in the English-speaking world by at least the eighteenth century. Some tracing of early usage also suggests that it appeared in seventeenth-century medical and anatomical writings in its original Latin form. It is therefore reasonable to view in situ as a term that gradually entered scholarly English during the early modern period. 

By the late nineteenth and early twentieth centuries, in situ had begun to establish itself as a technical term in medicine and in the sciences. In medicine, it became especially important in diagnostic expressions such as carcinoma in situ. This refers to abnormal cells that remain confined to the location where they first formed and have not yet invaded surrounding tissues. The U.S. National Cancer Institute, for example, defines in situ as meaning “in its original place” and explains carcinoma in situ as a condition in which abnormal cells are found only in the place where they first developed. 

At the same time, in situ also took on an important practical meaning in geology, civil engineering, and earth sciences. In these fields, it came to refer to the investigation of soil, rock, strata, and groundwater in their original field condition rather than after sampling and removal. 

From there, the term expanded into materials science, chemistry, and biology. In these areas, it came to function as an important methodological concept contrasted with ex situ, which refers to analysis performed after separating the sample from its original environment. Today, although exact quantitative counts vary depending on the database, it is clear that in situ has become a widely used and conceptually important term across scientific literature. 

Interdisciplinary Uses of In Situ 

In the natural sciences and engineering, in situ generally refers to methods of measurement or observation that preserve the site or original condition of the subject as much as possible. In geology, earth sciences, and civil engineering, investigations that directly measure the properties of soil, rock masses, strata, or ground stability in the field are described as in situ measurements. These are distinguished from analyses performed on samples transported to the laboratory. 

In biology and molecular biology, the term includes more than field studies of organisms in their natural habitats. It also includes techniques such as in situ hybridization, which identify the location of specific DNA or RNA while preserving the structural context of tissues and cells. In this sense, in situ does not merely indicate physical location. It refers to analysis that retains spatial context. 

The term also plays a major role in medicine and pathology. Expressions such as ductal carcinoma in situ, for example, refer to a condition in which cancer cells have not yet penetrated the basement membrane or invaded surrounding tissues. In other words, it is an official diagnostic category used to describe lesions that remain “in place.” 

In archaeology and cultural heritage preservation, in situ refers to artifacts or structures that remain in their original position and stratigraphic context. When an artifact is discovered without having been displaced, its spatial relationships and depositional context are preserved. This greatly increases the reliability of interpretation. In heritage preservation as well, in situ preservation is often regarded as the preferred principle whenever possible. UNESCO also treats preservation in the original location as the first option in the case of underwater cultural heritage. 

In linguistics, in situ is also an important technical term. In syntax, it refers to an element that remains in its original position within a sentence rather than being moved. For example, phenomena in which wh-expressions remain in their original position, as in Chinese, are described as wh-in situ. 

Taken together, these examples show that in situ is not limited to the natural sciences. It is used across many disciplines to express a broader commitment to preserving context. In that sense, in situ is not just a technical label, but also a methodological perspective shared across different forms of research. 

Why In Situ Matters in Catalysis 

In catalysis research, the concept of operando is often used alongside in situ. In general, in situ refers to an experimental setup in which the structure, composition, and surface species of a catalyst are measured under temperature, pressure, gas composition, solvent, or electrochemical potential conditions that are similar or identical to actual reaction conditions. 

By contrast, operando goes one step further. It refers to an approach in which catalytic performance indicators, such as conversion, selectivity, and current density, are measured at the same time that the catalyst’s structure or surface state is being tracked. Recent reviews in catalysis describe operando not simply as an observational cell, but as a reactor-like environment in which the reaction is actually carried out and performance is verified simultaneously. At the same time, however, the literature does not always draw a perfectly strict distinction between the two terms. They are often used in overlapping or partially interchangeable ways. 

In situ is especially important in catalysis because a catalyst is not a fixed solid during reaction. Instead, it is a dynamic system that changes continuously under operating conditions. In heterogeneous catalysis, factors such as temperature, gas atmosphere, electrochemical potential, and surface coverage of adsorbed species can all change the state of the catalyst. As these conditions vary, the catalyst may also change in oxidation state, coordination environment, particle structure, and surface arrangement. 

Because of this, ex situ analysis performed only before and after reaction can miss transient active species, surface intermediates, or reconstructed active surfaces that exist only during the reaction itself. In situ and operando techniques are therefore important because they allow researchers to follow these changes directly under working conditions. This leads to a more reliable understanding of how catalyst structure affects activity and reaction mechanisms. 

To address the limitations of static analysis, catalysis research uses a range of in situ and operando techniques. For example, in situ FT-IR and Raman spectroscopy are commonly used to track adsorbed surface species under reaction conditions. Surface-enhanced methods such as SERS, SERRS, and SEIRA can further improve sensitivity to interfacial species. X-ray absorption spectroscopy, including XANES and EXAFS, is widely used to follow changes in oxidation state and local structure of metal centers during reaction. In electrocatalysis, techniques such as UV–Vis, XAS, and electrochemical mass spectrometry (EC-MS) are often combined under applied potential to monitor both reaction intermediates and electrode surface states. 

These tools do more than simply show what is present. They make it possible to infer which adsorbed intermediates are formed and consumed during reaction, which reaction pathway is dominant, which oxidation state or coordination environment is associated with high activity, and which structural changes lead to deactivation. In other words, in situ and operando measurements allow reaction mechanisms and structure–activity relationships to be reconstructed under more realistic working conditions. This is why recent reviews in catalysis emphasize an integrated approach that combines performance evaluation, ex situ characterization, theoretical calculations, and in situ/operando measurements. 

This perspective is also useful when reinterpreting the integrated SCR–CESAR-1 system. If one could track NH₃-related intermediates and adsorbed species on the SCR catalyst surface under actual flue gas composition, humidity, temperature, and flow conditions, while simultaneously observing changes in carbamate species, bicarbonate species, and metal–amine interactions within the CESAR-1 absorbent solution, it would become possible to interpret both mechanism and performance much more closely to real operating conditions than with conventional static analysis. 

Furthermore, the in situ approach allows systems to be evaluated in laboratory environments that more closely resemble industrial settings. This makes it possible to identify reaction mechanisms and potential problems more precisely before actual process implementation. As a result, it can reduce unnecessary trial and error and lower the time and cost required in later stages of development. 

Re-reading My Paper Through an In Situ Perspective 

My research proposed an integrated process system in which an upstream SCR unit removes NOₓ in advance. This was intended to suppress the formation of harmful species in the downstream absorber–stripper system. However, the study still lacked a detailed explanation of which operating conditions would be most appropriate and which reactions would dominate at each stage. 

In this regard, the in situ approach could be highly useful. If prior data from industrial sites, such as flue gas composition, temperature, pressure, humidity, and flow conditions, are available, in situ experiments could be designed to analyze how the catalyst responds over time under those realistic conditions. 

In addition, if these results are combined with computer simulations such as DFT (Density Functional Theory), MD (Molecular Dynamics), microkinetic modeling, CFD (Computational Fluid Dynamics), or Aspen Plus process simulation, they could provide a much stronger basis for catalyst design and system evaluation. More importantly, this combined approach could connect mechanism, catalyst stability, and process design within a single analytical framework. 

A possible next step following this paper would therefore be to focus on the three core sections of the proposed SCR–CESAR integrated system: the upstream SCR unit, the absorber, and the stripper. These sections should be treated as both individually analyzable and mutually connected parts of the overall process. 

If real operating data from industrial sites, such as flue gas composition, temperature, pressure, humidity, and flow rate, could be obtained for each section, it would become possible to combine in situ analysis with computer simulation in order to determine more realistically which reactions and behaviors dominate in each part of the system. In the long run, this approach could open the way to developing plant-specific optimization strategies for different industrial sites according to their operating environments.