Two-dimensional (2D) crystals have developed into a popular mainstream research topic which is interesting for basic research and many applications. Gas-surface interactions, as reviewed here, are important for catalysis including noble metal-free catalysts, materials science, and surface science as well as environmental and energy technologies. Basic science concerns fundamental differences of 2D crystals and bulk materials as well as e.g. how the substrate of epitaxial 2D crystals affects their surface properties.

Most of the attention so far obtained (gas-phase) water adsorption which always was an evergreen in surface science. However, studies about small inorganic/organic molecule adsorption (CO, CO₂, NO_x, O₂, H, rare gases, H₂S, SO₂, alkanes, benzene, alcohols, thiophene, etc.) and surface reactions on 2D crystals (CO oxidation, ethylene epoxidation, oxygen reduction reaction, SO₂ and H₂SO₃ oxidation) started to appear in the literature as well. This review describes all of these probe molecules, but focuses on experimental and theoretical surface science model studies usually conducted at ultra-high vacuum (UHV).

The review focusses on graphene and functionalized graphene (graphene oxide, N-graphene, etc.) since the bulk of the literature deals with that system. However, included in fair detail are also many other 2D crystals such as silicatene, zeolite films (doped silicatene), metal dichalcogenides (such as MoS₂, WS₂), boron nitride, MXenes, germanene, silicene, TiO₂, graphane, graphone, and portlandene.

As a prototypical example, in recent projects, the wetting properties of e.g. graphene for water were controversially discussed. Therefore, a long chapter is devoted to water on graphene. That dispute was originally based on contact angle measurements at ambient pressure. In the meanwhile detailed surface science works including theoretical modelling are available. Literature on other carboneous surfaces such as HOPG (see list of acronyms) will be considered as a reference. Related works are also visible for other inorganic 2D crystals such as silicatene, i.e., 2D-SiO₂, or 2D-MoS₂ as well as functionalized 2D crystals (i.e. graphene oxide, N-doped graphene, graphane, etc.). Hydrophobic systems also are interesting for applications.

Although included in this review, but not described in very detail are electro chemistry studies, projects in the liquid phase, photo-chemistry, high pressure catalysis, and pure engineering studies (membranes, separation, fuel cells). However, in comparison with 2D crystals and to perhaps motivate related UHV surface chemistry projects in the future many of these projects were included to some extent.

As a broader objective, this review summarizes the currently available knowledge needed to extend the use of 2D materials beyond the utilization of their remarkable electronic and mechanical properties.

二维（2D）晶体已发展成为一个流行的主流研究主题，这对于基础研究和许多应用而言都非常有趣。如本文所述，气体表面相互作用对催化非常重要，包括无贵金属催化剂，材料科学，表面科学以及环境和能源技术。基础科学关注2D晶体和块状材料的根本差异，以及外延2D晶体的基底如何影响其表面性能。

迄今为止，大多数注意力都集中在（气相）水吸附上，这在表面科学中一直是常青树。但是，关于二维上的无机/有机分子小吸附（CO，CO ₂，NO _x，O ₂，H，稀有气体，H ₂ S，SO ₂，烷烃，苯，醇，噻吩等）和表面反应的研究晶体（CO氧化，乙烯环氧化，氧还原反应，SO ₂和H ₂ SO ₃氧化）也开始出现在文献中。这篇综述描述了所有这些探针分子，但侧重于通常在超高真空（UHV）下进行的实验和理论表面科学模型研究。

由于大量文献都涉及该系统，因此本文的研究重点是石墨烯和功能化石墨烯（氧化石墨烯，N-石墨烯等）。但是，还包括许多其他2D晶体，例如硅酸盐，沸石膜（掺杂硅酸盐），金属二卤化物（例如MoS ₂，WS ₂），氮化硼，MXenes，锗烯，硅石，TiO ₂，石墨烯，石墨烯和波特兰烯。

作为一个典型的例子，在最近的项目中，有争议的讨论了例如石墨烯对水的润湿特性。因此，有一章专门讨论了石墨烯上的水。该争议最初是基于在环境压力下的接触角测量得出的。同时，可以获得包括理论建模在内的详细的表面科学著作。其他含碳表面的文献，例如HOPG（请参阅首字母缩写词列表）将被视为参考。对于其他无机2D晶体（例如，硅酮，即2D-SiO ₂或2D-MoS ₂）以及功能化的2D晶体（即，氧化石墨烯，N掺杂的石墨烯，石墨烷等），相关工作也可见。疏水性系统对于应用也很有趣。

尽管包括在本综述中，但并未详细介绍电化学研究，液相项目，光化学，高压催化和纯工程研究（膜，分离，燃料电池）。但是，与2D晶体相比，为了将来可能激发相关的特高压表面化学项目，在一定程度上包括了许多此类项目。

作为更广泛的目标，本综述总结了将2D材料的使用扩展到超出其非凡的电子和机械特性的应用所需的当前可用知识。